Comparison of plaque reduction neutralisation test (PRNT) and measles virus-specific IgG ELISA for assessing immunogenicity of measles vaccination

Innovations in dengue virus detection: An overview of conventional and electrochemical biosensor approaches

Globally, people are in great threat due to the highly spreading of viral infectious diseases. Every year like 100-300 million cases of infections are found, and among them, above 80% are not recognized and irrelevant. Dengue virus (DENV) is an arbovirus infection that currently infects people most frequently. DENV encompasses four viral serotypes, and they each express comparable sign. From a mild febrile sickness to a potentially fatal dengue hemorrhagic fever, dengue can induce a variety of symptoms. Presently, the globe is being challenged by the untimely identification of dengue infection. Therefore, this review summarizes advances in the detection of dengue from conventional methods (nucleic acid-based, polymerase chain reaction-based, and serological approaches) to novel biosensors. This work illustrates an extensive study of the current designs and fabrication approaches involved in the formation of electrochemical biosensors for untimely identifications of dengue. Additionally, in electrochemical sensing of DENV, we skimmed through significances of biorecognition molecules like lectins, nucleic acid, and antibodies. The introduction of emerging techniques such as the CRISPR/Cas' system and their integration with biosensing platforms has also been summarized. Furthermore, the review revealed the importance of electrochemical approach compared with traditional diagnostic methods.

Neutralizing antibody titers against D8 genotype and persistence of measles humoral and cell-mediated immunity eight years after the first dose of measles, mumps, and rubella vaccine in Brazilian children

OBJECTIVE

Assess the level of measles vaccine-induced neutralizing antibodies against the D8 genotype and the persistence of humoral and cell-mediated immunity in children who received their first dose of the measles, mumps, and rubella vaccine eight years previously.

METHODS

Measles-specific IgG and neutralizing antibodies were determined in serum using ELISA and plaque reduction neutralization test, respectively. Cellular response was evaluated from peripheral blood mononuclear cells (PBMC). IFN-γ-secreting cells, memory B and T cells, and immunological mediators were assayed by ELISpot, flow cytometry, and multiplex liquid microarray assay, respectively.

RESULTS

Antibody concentrations declined over time; however, the vaccine-induced neutralizing antibodies' effect against D8 and vaccinal genotypes persisted. PBMC stimulated with the vaccine virus exhibited specific IFN- γ-measles-secreting responses in most participants. Participants with high levels of neutralizing antibodies showed a higher proportion of activated B cells compared to participants with low levels of neutralizing antibodies, while proportions of memory CD4+ and CD8+ T cells were similar between these groups. PBMC supernatant cytokine levels showed a significant difference between stimulated and non-stimulated conditions for IL-2, TNF-α, IL-10, and CXCL10.

CONCLUSION

Despite the decline in antibody concentrations over time, the participants still demonstrated neutralizing capacity against the measles D8 genotype five to eight years after the second dose of the measles, mumps, and rubella vaccine. Additionally, most of the enrolled children exhibited cell-mediated immunity responses to measles virus stimulation.

Estimating cutoff values for diagnostic tests to achieve target specificity using extreme value theory

BACKGROUND

Rapidly developing tests for emerging diseases is critical for early disease monitoring. In the early stages of an epidemic, when low prevalences are expected, high specificity tests are desired to avoid numerous false positives. Selecting a cutoff to classify positive and negative test results that has the desired operating characteristics, such as specificity, is challenging for new tests because of limited validation data with known disease status. While there is ample statistical literature on estimating quantiles of a distribution, there is limited evidence on estimating extreme quantiles from limited validation data and the resulting test characteristics in the disease testing context.

METHODS

We propose using extreme value theory to select a cutoff with predetermined specificity by fitting a Pareto distribution to the upper tail of the negative controls. We compared this method to five previously proposed cutoff selection methods in a data analysis and simulation study. We analyzed COVID-19 enzyme linked immunosorbent assay antibody test results from long-term care facilities and skilled nursing staff in Colorado between May and December of 2020.

RESULTS

We found the extreme value approach had minimal bias when targeting a specificity of 0.995. Using the empirical quantile of the negative controls performed well when targeting a specificity of 0.95. The higher target specificity is preferred for overall test accuracy when prevalence is low, whereas the lower target specificity is preferred when prevalence is higher and resulted in less variable prevalence estimation.

DISCUSSION

While commonly used, the normal based methods showed considerable bias compared to the empirical and extreme value theory-based methods.

CONCLUSIONS

When determining disease testing cutoffs from small training data samples, we recommend using the extreme value based-methods when targeting a high specificity and the empirical quantile when targeting a lower specificity.

The third dose of measles-containing vaccine induces robust immune responses against measles in young seronegative healthcare workers who had previous two-dose measles vaccination

BACKGROUND

Despite the low measles antibody positivity rate among young healthcare workers (HCWs) who have previously received two doses of a measles-containing vaccine (MCV), whether an additional dose of MCV acts as a booster remains unknown. Thus, we aimed to evaluate the immune responses to a third dose of MCV in young HCWs.

METHODS

Hospital-wide measles seroprevalence was assessed using enzyme-linked immunosorbent assay (ELISA). The immunogenicity of a third dose of MCV was determined in young seronegative HCWs (born between 1986 and 1997) who had previously received a two-dose measles vaccination.

RESULTS

A total of 3033 (92.6%) HCWs had anti-measles immunoglobulin G. The lowest seropositivity rate was observed in HCWs aged 20-24 years (87.7%). In this group, HCWs who received a third dose of MCV had higher seropositivity than those who received a second dose (89.5% vs. 75.4%). A third dose of MCV was administered to 18 HCWs who did not have anti-measles IgG despite two doses. Neutralizing antibody titers increased significantly 4 weeks after the third vaccination. Although neutralizing antibody titers decreased 1 year post vaccination, 17 (94.4%) HCWs had medium (121-900 mIU/mL) or high (>900 mIU/mL) levels. Furthermore, the third dose of MCV increased the measles virus-specific T-cell effector function.

CONCLUSIONS

The third dose of MCV induced a strong immune response against measles in young seronegative HCWs who had previously received a two-dose measles vaccination.

Comparison of measles IgG enzyme immunoassays (EIA) versus plaque reduction neutralization test (PRNT) for measuring measles serostatus: a systematic review of head-to-head analyses of measles IgG EIA and PRNT

BACKGROUND

As countries move towards or achieve measles elimination status, serosurveillance is an important public health tool. However, a major challenge of serosurveillance is finding a feasible, accurate, cost-effective, and high throughput assay to measure measles antibody concentrations and estimate susceptibility in a population. We conducted a systematic review to assess, characterize, and - to the extent possible - quantify the performance of measles IgG enzyme-linked assays (EIAs) compared to the gold standard, plaque reduction neutralization tests (PRNT).

METHODS

We followed the PRISMA statement for a systematic literature search and methods for conducting and reporting systematic reviews and meta-analyses recommended by the Cochrane Screening and Diagnostic Tests Methods Group. We identified studies through PubMed and Embase electronic databases and included serologic studies detecting measles virus IgG antibodies among participants of any age from the same source population that reported an index (any EIA or multiple bead-based assays, MBA) and reference test (PRNT) using sera, whole blood, or plasma. Measures of diagnostic accuracy with 95% confidence intervals (CI) were abstracted for each study result, where reported.

RESULTS

We identified 550 unique publications and identified 36 eligible studies for analysis. We classified studies as high, medium, or low quality; results from high quality studies are reported. Because most high quality studies used the Siemens Enzygnost EIA kit, we generate individual and pooled diagnostic accuracy estimates for this assay separately. Median sensitivity of the Enzygnost EIA was 92.1% [IQR = 82.3, 95.7]; median specificity was 96.9 [93.0, 100.0]. Pooled sensitivity and specificity from studies using the Enzygnost kit were 91.6 (95%CI: 80.7,96.6) and 96.0 (95%CI: 90.9,98.3), respectively. The sensitivity of all other EIA kits across high quality studies ranged from 0% to 98.9% with median (IQR) = 90.6 [86.6, 95.2]; specificity ranged from 58.8% to 100.0% with median (IQR) = 100.0 [88.7, 100.0].

CONCLUSIONS

Evidence on the diagnostic accuracy of currently available measles IgG EIAs is variable, insufficient, and may not be fit for purpose for serosurveillance goals. Additional studies evaluating the diagnostic accuracy of measles EIAs, including MBAs, should be conducted among diverse populations and settings (e.g., vaccination status, elimination/endemic status, age groups).

What's in a number? The value of titers as routine proof of immunity for medical students

OBJECTIVES

To assess the guideline concordance of medical school requirements for students' proof-of-immunity in the United States (US) and Canada.

METHODS

National guidelines for healthcare worker proof-of-immunity to measles, mumps, rubella, and varicella were compared to admission requirements for 62 US and 17 Canadian medical schools.

RESULTS

All surveyed schools accepted at least one recommended form of proof-of-immunity, however, contrary to national guidelines, 16% of surveyed US schools asked for a serologic titer, and only 73-79% US schools accepted vaccination as the sole proof-of-immunity.

CONCLUSIONS

The requirement of numerical, non-standardized serologic testing highlights an oversight in medical school admissions documentation. The requirement for quantitative values to demonstrate immunity is not practical from a laboratory standpoint, and is not needed to show individual immunity to these vaccine-preventable diseases. Until a more standardized process is adopted, laboratories will need to provide clear documentation and direction for quantitative titer requests.

Baculovirus displaying SARS-CoV-2 spike RBD promotes neutralizing antibody production in a mouse model

BACKGROUND

There is always a need for a safe and efficient vaccine platform, especially when facing a pandemic such as COVID-19. Most of the SARS-CoV-2-based vaccines are based on the full spike protein, which is presented as a trimerized protein, and many viral vector vaccines express the spike protein into the host cells and do not display it on virus surfaces. However, the spike receptor-binding domain (RBD)-based vaccines are efficient and are currently under investigation and clinical trials.

METHODOLOGY

In this study, we are testing the efficacy of the RBD displayed on a baculovirus as a mean to formulate a safe and stable carrier to induce the immune system against SARS-CoV-2. Therefore, two pseudotyped baculoviruses were constructed to display the RBD, AcRBD-sfGFP-64, and AcRBD-sfGFP-V, using two different displaying strategies based on gp64 and VSV-G envelope glycoproteins, from Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and vesicular stomatitis virus (VSV), respectively. BALB/C mice were immunized with the pseudotyped baculoviruses in a dose-optimized manner. Dot blot and Western blot were used to screen and validate the polyclonal antibodies' specificity to the SARS-CoV-2 RBD. A plaque reduction neutralization test (PRNT) was used to measure the sera neutralization capacity against a SARS-CoV-2 wild-type isolate from Egypt. ELISA was used to quantify certain cytokines for the assessment of the immune response.

RESULT

The outcome of our investigation showed that the monomeric RBD proteins were properly displayed on baculovirus and efficiently triggered the mouse immune system. The produced sera efficiently neutralized about 50% of SARS-CoV-2 in more than 100-fold serum dilution. The immunized mice showed a significant increase (p<0.01) in the levels of IL-2 and IFN-γ and a significant decrease (p<0.01) and (p<0.001) in the levels of IL-4 and IL-10, respectively, which suggest that AcRBD-sfGFP-64 and AcRBD-sfGFP-V induce Th1 cellular immune response.

CONCLUSION

The produced recombinant viruses can induce the immune response without adjuvant, which needs dose optimization and further stability tests. Neutralizing antibodies were induced without affecting the health of immunized mice. Th1 response can be attainable through the system, which is of great benefit in SARS CoV-2 infection and the system can be tested for future applications including vaccine development and polyclonal antibody production.

Waning of maternal antibody against measles virus in Shufu, China

BACKGROUND

As measles vaccination coverage has increased, measles infection has shifted to the population of infants. We conducted a follow-up seroepidemiological study among mothers and their infants to evaluate measles seroprevalence and the persistence of maternal measles antibody in Shufu, Kashgar from 2018 to 2020.

METHODS

Maternal venous blood and cord blood was obtained among mothers and their infants at 0, 3, 5, 8, 9, and 12 months of age. An enzyme-linked immunosorbent assay was used for quantitative measurement of measles antibodies. We analyzed the correlation between maternal and neonatal measles antibodies, and antibodies persistence after infants were born.

RESULTS

The overall neonatal maternal ratio was 2.38 (95%CI: 2.05-2.71). The measles antibodies for mothers and newborns were 438.93 IU/mL (95%CI: 409.47-470.51 IU/mL) and 440.10 IU/mL (95%CI: 410.82-471.48 IU/mL), respectively. Neonatal measles antibodies were dropping after birth and then beginning to increase starting at 8 months of age.

CONCLUSIONS

Infant measles antibody levels progressively declined after birth regardless of maternal measles antibody levels. Efforts should be carried out to eliminate measles.

Serological Evidence of Orthopoxvirus Infection in Neotropical Primates in Brazil

The genus Orthopoxvirus (OPXV) of the family Poxviridae comprises several viruses that are capable of infecting a wide range of hosts. One of the most widespread OPXVs is the Vaccinia virus (VACV), which circulates in zoonotic cycles in South America, especially in Brazil, infecting domestic and wild animals and humans and causing economic losses as well as impacting public health. Despite this, little is known about the presence and/or exposure of neotropical primates to orthopoxviruses in the country. In this study, we report the results of a search for evidence of OPVX infections in neotropical free-living primates in the state of Minas Gerais, southeast Brazil. The sera or liver tissues of 63 neotropical primates were examined through plaque reduction neutralization tests (PRNT) and real-time PCR. OPXV-specific neutralizing antibodies were detected in two sera (4.5%) from Callithrix penicillata, showing 55% and 85% reduction in plaque counts, evidencing their previous exposure to the virus. Both individuals were collected in urban areas. All real-time PCR assays were negative. This is the first time that evidence of OPXV exposure has been detected in C. penicillata, a species that usually lives at the interface between cities and forests, increasing risks of zoonotic transmissions through spillover/spillback events. In this way, studies on the circulation of OPXV in neotropical free-living primates are necessary, especially now, with the monkeypox virus being detected in new regions of the planet.

Low Measles Seropositivity Rate among Thai Adolescents in the Thai National Immunization Program

To achieve the goal of measles elimination, herd immunity with 95% seroprotection in the community is required. This study aimed to describe the measles seropositivity rate among Thai children and adolescents. A cross-sectional study was conducted among children aged 3−18 years in Bangkok and its suburbs. Measles IgG antibodies were measured using a EUROIMMUN enzyme-linked immunosorbent assay kit. Seropositivity is defined as a measles IgG titer of ≥200 IU/L, due to a correlation with a >85% positive rate with a plaque reduction neutralizing titer of >120. Factors associated with seropositivity were analyzed using logistic regression analysis. From May to July 2020, 570 children with a median (IQR) age of 11.7 (9.4−14.8) years were enrolled. The geometric mean titer (GMT) of anti-measles IgG was 281 IU/L (95% CI; 257−306). The proportion of children with seropositivity was inversely correlated with age; 3−5 years 85.3%, 6−9 years 72.5%, 10−14 years 50.7%, and 15−18 years 56.3%. Adolescents aged 10−18 years had a lower measles seropositivity rate compared with young children; aOR 0.29 (95% CI 0.17−0.48). Only half of the adolescents who received two doses of measles-containing vaccine maintained measles IgG above the seropositive level. A measles booster dose for young adults may be needed to achieve the measles elimination goal.

Updates on Measles Incidence and Eradication: Emphasis on the Immunological Aspects of Measles Infection

Measles is an RNA virus infectious disease mainly seen in children. Despite the availability of an effective vaccine against measles, it remains a health issue in children. Although it is a self-limiting disease, it becomes severe in undernourished and immune-compromised individuals. Measles infection is associated with secondary infections by opportunistic bacteria due to the immunosuppressive effects of the measles virus. Recent reports highlight that measles infection erases the already existing immune memory of various pathogens. This review covers the incidence, pathogenesis, measles variants, clinical presentations, secondary infections, elimination of measles virus on a global scale, and especially the immune responses related to measles infection.

Measles susceptibility in maternal-infant dyads-Bamako, Mali

Measles is endemic in Africa; measles mortality is highest among infants. Infant measles antibody titer at birth is related to maternal immune status. Older mothers are likelier to have had measles infection, which provides higher antibody titers than vaccine-induced immunity. We investigated the relationship between maternal age and measles susceptibility in mother-infant pairs in Mali through six months of infancy. We measured serum measles antibodies in 340 mother-infant pairs by plaque reduction neutralization test (PRNT) and calculated the proportion of mothers with protective titers (>120 mIU/mL) at delivery and the proportion of infants with protective titers at birth, and at three and six months of age. We explored associations between maternal age and measles antibodies in mothers and infants at the timepoints noted. Ten percent of Malian newborns were susceptible to measles; by six months nearly all were. Maternal and infant antibody titers were highly correlated. At delivery, 11% of mothers and 10% of newborns were susceptible to measles. By three and six months, infant susceptibility increased to 72% and 98%, respectively. Infants born to younger mothers were most susceptible at birth and three months. Time to susceptibility was 6.6 weeks in infants born to mothers with measles titer >120-<430 mIU/mL versus 15.4 weeks when mothers had titers ≥430 mIU/mL. Maternal and newborn seroprotective status were positively correlated. Improved strategies are needed to protect susceptible infants from measles infection and death. Increasing measles immunization coverage in vaccine eligible populations, including nonimmune reproductive-aged women and older children should be considered.

Prevalence of measles antibodies among migrant workers in Singapore: a serological study to identify susceptible population subgroups

Background

In 2019, two clusters of measles cases were reported in migrant worker dormitories in Singapore. We conducted a seroprevalence study to measure the level of susceptibility to measles among migrant workers in Singapore.

Methods

Our study involved residual sera of migrant workers from seven Asian countries (Bangladesh, China, India, Indonesia, Malaysia, Myanmar and the Philippines) who had participated in a survey between 2016 and 2019. Immunoglobulin G (IgG) antibody levels were first measured using a commercial enzyme-linked immunosorbent assay (ELISA) test kit. Those with equivocal or negative IgG results were further evaluated using plaque reduction neutralization test (PRNT).

Results

A total of 2234 migrant workers aged 20–49 years were included in the study. The overall prevalence of measles IgG antibodies among migrant workers from the seven Asian countries was 90.5% (95% confidence interval 89.2–91.6%). The country-specific seroprevalence ranged from 80.3 to 94.0%. The seroprevalence was significantly higher among migrant workers born in 1965–1989 than those born in 1990–1999 (95.3% vs. 86.6%, p < 0.0005), whereas there was no significant difference by gender (90.8% in men vs. 89.9% in women, p = 0.508). 195 out of 213 samples with equivocal or negative ELISA results were tested positive using PRNT.

Conclusion

The IgG seroprevalence in migrant workers was below the herd immunity threshold of 95% for measles. Sporadic outbreaks may occur in susceptible individuals due to high transmissibility of measles virus. Seroprevalence surveys can help identify susceptible subgroups for vaccination.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07066-2.

Assessing SARS-CoV-2 Neutralizing Antibodies after BNT162b2 Vaccination and Their Correlation with SARS-CoV-2 IgG Anti-S1, Anti-RBD and Anti-S2 Serological Titers

The humoral response through neutralizing antibodies (NAbs) is a key component of the immune response to COVID-19. However, the plaque reduction neutralization test (PRNT), the gold standard for determining NAbs, is technically demanding, time-consuming and requires BSL-3 conditions. Correlating the NAbs and total antibodies levels, assessed by generalized and automated serological tests, is crucial. Through a commercial surrogate virus neutralization test (sVNT), we aimed to evaluate the production of SARS-CoV-2 NAbs in a set of vaccinated healthcare workers and to correlate these NAbs with the SARS-CoV-2 IgG anti-S1, anti-RBD and anti-S2 serological titers. We found that 6 months after vaccination, only 74% maintain NAbs for the Wuhan strain/UK variant (V1) and 47% maintain NAbs for the South African and Brazil variants (V2). Through Spearman's correlation, we found the following correlations between the percentage of inhibition of NAbs and the SARS-CoV-2 IgG II Quant (Abbott Laboratories, Chicago, IL, USA) and BioPlex 2200 SARS-CoV-2 IgG Panel (Bio-Rad, Hercules, CA, USA) immunoassays: rho = 0.87 (V1) and rho = 0.73 (V2) for anti-S1 assessed by Abbott assay; rho = 0.77 (V1) and rho = 0.72 (V2) for anti-S1, rho = 0.88 (V1) and rho = 0.82 (V2) for anti-RBD, and rho = 0.68 (V1) and rho = 0.60 (V2) for anti-S2 assessed by BioPlex assay (p < 0.001 for all). In conclusion, we found a strong correlation between this fast, user-friendly, mobile and bio-safe sVNT and the serological immunoassays.

Comparison of Antibody Response Elicited by ChAdOx1 and BNT162b2 COVID-19 Vaccine

BACKGROUND

ChAdOx1 and BNT162b2 vaccines are currently commonly used against coronavirus disease 2019 worldwide. Our study was designed to determine the serostatus and relative levels of anti-S and neutralizing antibodies in patients who were administered either ChAdOx1 or BNT162b2 vaccine. In addition, we investigated whether the antibody response to each vaccine differed according to sex and age.

METHODS

Healthcare workers (HCWs) at a general hospital who were vaccinated with two doses of either ChAdOx1 or BNT162b2 were invited to participate in this prospective cohort study. Blood samples of HCWs vaccinated with both ChAdOx1 doses over a period of 12 weeks were collected at weeks 4 and 8 post first vaccination and 2 weeks post second vaccination. Blood samples of HCWs vaccinated with BNT162b2 were collected in the third week after the first dose, and the second dose was then administered on the same day; two weeks post second dose (5 weeks after the first dose), blood samples were collected to assess the antibody response. The titers of anti-S antibodies against the severe acute respiratory syndrome coronavirus 2 spike (S) protein receptor-binding domain and the neutralizing antibodies in the collected blood were evaluated.

RESULTS

Of the 309 HCWs enrolled in the study, 205 received ChAdOx1 and 104 received BNT162b2. Blood samples from participants receiving either the ChAdOx1 or BNT162b2 vaccine exhibited substantial anti-S and neutralizing antibody seropositivity subsequent to the second dose. All participants (100%) from both vaccine groups were seropositive for anti-S antibody, while 98% (201/205) of ChAdOx1-vaccinated individuals and 100% (104/104) of BNT162b2-vaccinated individuals were seropositive for neutralizing antibodies. The median levels of anti-S and neutralizing antibodies were significantly higher in the BNT162b2-vaccinated group than the ChAdOx1-vaccinated group; in particular, anti-S antibody titers of 1,020 (interquartile range, 571.0-1,631.0) U/mL vs. 2,360 (1,243-2,500) U/mL, P < 0.05, were recorded for the ChAdOx1 and BNT162b2 groups, respectively, and neutralizing antibody titers of 85.0 (65.9-92.1%) vs. 95.8 (94.4-96.6%), P < 0.05, were recorded for the ChAdOx1 and BNT162b2 groups, respectively. In the ChAdOx1 vaccine group, the neutralizing antibody level was significantly higher in women than in men (85.7 [70.3-92.5%] vs. 77.7 [59.2-91.0%], P < 0.05); however, the neutralizing antibody titer in the BNT162b2 vaccine group did not vary between the two sexes (95.9 [95.2-96.6%] vs. 95.2 [93.5-96.3%], P = 0.200). Analysis of the correlation of antibody profiles with age revealed that the levels of anti-S antibodies and signal inhibition rate (SIR) of neutralizing antibodies decreased significantly with age.

CONCLUSION

Both the ChAdOx1- and BNT162b2-vaccinated groups showed high seropositivity for anti-S and neutralizing antibodies. The SIR of neutralizing antibodies in the ChAdOx1 vaccine group was higher in women than in men. Enhanced antibody responses were observed in participants vaccinated with BNT162b2 compared to those vaccinated with the ChAdOx1 vaccine.

Measles seroprevalence among Dutch travelling families

BACKGROUND

While measles vaccination is widely implemented in national immunisation programmes, measles incidence rates are increasing worldwide. Dutch inhabitants who were born between 1965-1975 may have fallen between two stools, lacking protection from a natural infection, and having missed the introduction of the measles vaccination schedule. With this study we aim to find the measles seroprevalence in travellers born between 1965 and 1975, compared to those born before 1965 and after 1975.

METHODS

Families travelling to Eastern Europe or outside Europe during the preceding year were recruited via Dutch secondary schools between 2016 and 2018. Their vaccination status was assessed using questionnaires, vaccination records and measles serology in dried blood spot (DBS) eluates. Measles virus antibody concentrations were determined with an ELISA (EUROIMMUNE®) and a subset was retested with a focus reduction neutralization assay (FRNT).

RESULTS

In 188 (79%) of the 239 available DBS eluates, the ELISA could detect sufficient measles virus-specific IgG antibodies. Of the negative samples that were retested with FRNT, 85% remained negative, resulting in an overall seroprevalence of 82% [95% CI 76-86]. Children had a lower seroprevalence (72%) than adults (87%). Travellers born between 1965 and 1975 were protected in 89%.

CONCLUSIONS

In this study, we report a measles seroprevalence of 82% among Dutch travelling families. Remarkably, seroprevalence rates were lowest in children (12-18 years) instead of travellers born between 1965 and 1975. Although a fraction of people without detectable antibodies may be protected by other immune mechanisms, these data suggest that measles (re)vaccination should be considered for travellers to endemic regions.

Quantification of SARS-CoV-2 neutralizing antibody by wild-type plaque reduction neutralization, microneutralization and pseudotyped virus neutralization assays

Virus neutralization assays measure neutralizing antibodies in serum and plasma, and the plaque reduction neutralization test (PRNT) is considered the gold standard for measuring levels of these antibodies for many viral diseases. We have developed procedures for the standard PRNT, microneutralization assay (MNA) and pseudotyped virus neutralization assay (PNA) for severe acute respiratory syndrome coronavirus 2. The MNA offers advantages over the PRNT by reducing assay time, allowing increased throughput and reducing operator workload while remaining dependent upon the use of wild-type virus. This ensures that all severe acute respiratory syndrome coronavirus 2 antigens are present, but Biosafety Level 3 facilities are required. In addition to the advantages of MNA, PNA can be performed with lower biocontainment (Biosafety Level 2 facilities) and allows for further increases in throughput. For each new vaccine, it is critical to ensure good correlation of the neutralizing activity measured using PNA against the PRNT or MNA. These assays have been used in the development and licensure of the ChAdOx1 nCoV-19 (AstraZeneca; Oxford University) and Ad26.COV2.S (Janssen) coronavirus disease 2019 vaccines and are critical for demonstrating bioequivalence of future vaccines.

[How well are patients with inflammatory rheumatic diseases protected against measles?]

Hintergrund

Patienten mit entzündlich rheumatischen Erkrankungen haben aufgrund ihrer Autoimmunerkrankung, aber auch bedingt durch die immunsuppressive Medikation ein erhöhtes Infektrisiko. Obwohl Impfungen in der Primärprophylaxe von Infektionen bekanntermaßen effektiv sind, ist die Impfrate in Deutschland generell zu niedrig. Wegen des zuletzt zunehmenden, teils epidemieartigen Auftretens von Masern ist die Lebendimpfung gegen Masern in Deutschland seit Kurzem gesetzlich vorgeschrieben.

Fragestellung

Wie viele Patienten mit entzündlich rheumatischen Erkrankungen sind aktuell ausreichend gegen Masern geschützt?

Methode

Patienten mit entzündlich rheumatischen Erkrankungen des Rheumazentrums Ruhrgebiet wurden zwischen Dezember 2017 und Oktober 2018 prospektiv und konsekutiv eingeschlossen. Dabei wurden Daten zu Erkrankung und Therapie auf Ebene von Substanzklassen sowie die Impf- und Infektanamnese erhoben. Alle Angaben zu Impfungen wurden im Impfpass kontrolliert. Antikörpertiter gegen Masern wurden mit ELISA bestimmt. Als Schwellenwert für einen ausreichenden Schutz gegen Masern wurden 150 mIU/ml festgelegt.

Ergebnis

Von 975 Patienten konnten 540 (55,4 %) einen Impfausweis vorlegen. Bei 201 Patienten mit Ausweis (37,2 %) lagen dokumentierte Impfungen seit Geburt vor. Insgesamt hatten 45 von 267 nach 1970 geborene Patienten (16,9 %) einen suffizienten Impfschutz gegen Masern. Die anamnestischen Angaben zu einer Masernerkrankung in der Kindheit differenzierten nicht zwischen Patienten mit und ohne protektiven Masern-IgG-Antikörpern. Protektive Masern-IgG-Antikörper wurden bei 901 Patienten von 928 Patienten mit Messung der Masern-IgG-Antikörperspiegel (97,1 %) nachgewiesen. Die unterschiedlichen Wirkprinzipien der aktuellen immunsuppressiven Therapie hatten darauf keinen Einfluss.

Diskussion

Diese Daten zeigen, dass mindestens 2,9 % der Patienten keinen ausreichenden Schutz gegen Masern haben. Interessanterweise hatte die Mehrheit der nach 1970 geborenen Patienten protektive Antikörper trotz fehlenden Impfschutzes gegen Masern. Die Anstrengungen sowohl im primär- als auch im fachärztlichen Bereich sollten dringend verstärkt werden, um eine adäquate Infektionsprophylaxe bei besonders gefährdeten Patienten gewährleisten zu können.

Nanoformulated Single-Stranded RNA-Based Adjuvant with a Coordinative Amphiphile as an Effective Stabilizer: Inducing Humoral Immune Response by Activation of Antigen-Presenting Cells

As agonists of TLR7/8, single-stranded RNAs (ssRNAs) are safe and promising adjuvants that do not cause off-target effects or innate immune overactivation. However, low stability prevents them from mounting sufficient immune responses. This study evaluates the adjuvant effects of ssRNA derived from the cricket paralysis virus intergenic region internal ribosome entry site, formulated as nanoparticles with a coordinative amphiphile, containing a zinc/dipicolylamine complex moiety as a coordinative phosphate binder, as a stabilizer for RNA-based adjuvants. The nanoformulated ssRNA adjuvant was resistant to enzymatic degradation in vitro and in vivo, and that with a coordinative amphiphile bearing an oleyl group (CA-O) was approximately 100 nm, promoted effective recognition, and improved activation of antigen-presenting cells, leading to better induction of neutralizing antibodies following single immunization. Hence, CA-O may increase the efficacy of ssRNA-based adjuvants, proving useful to meet the urgent need for vaccines during pathogen outbreaks.

Comparison of CaptiaTM Measles IgG Assay with Vidas® Measles IgG Assay for determination of immune protection status against measles virus

BACKGROUND

Correlation of the assay cut-off values for Captia^TM Measles IgG and the Vidas® Measles IgG assays with the World Health Organization recommended immunoprotective level of ≥120 mIU/mL is not stated by the manufacturers. Lack of such information may affect interpretation of immune protection (IP) for measles.

OBJECTIVE

The aim of this study was to compare the relative performance of the Captia^TM Measles IgG assay and the Vidas® Measles IgG assay for determination of IP against measles virus.

STUDY DESIGN

Correlation of the cut-off value of both assays with the immunoprotective level was determined with the 3rd WHO Measles IgG International Standard. One hundred clinical samples including frozen and fresh were tested with both assays. The positive percentage agreement (PPA) based on the manufacturers' interpretation and the WHO recommended immunoprotective level was compared.

RESULTS

Samples tested positive by the Captia^TM assay were at or above the immunoprotective level while those tested equivocal and positive by the Vidas® assay were immune protective. The overall PPA between both assays was 78.31 % (95 % CI = 67.91-86.61%). When Vidas® equivocal results were regarded as immunoprotective, the overall IP agreement was 96.39 % (95 % CI = 89.80-99.25 %).

CONCLUSIONS

Captia^TM assay was more sensitive than the Vidas® assay in determination of IP against measles virus. Testing of measles immunity with the Vidas® Measles IgG assay might underestimate the IP unless equivocal results were regarded as immunoprotective.

Seroprevalence of vaccine-preventable diseases among children and adolescents in Singapore: Results from the National Paediatric Seroprevalence Survey 2018

OBJECTIVES

The Ministry of Health (MOH), Singapore, conducted the National Paediatric Seroprevalence Survey 2018 (NPSS 2018) to estimate the latest immunity levels against measles, rubella, varicella, diphtheria, tetanus and hepatitis B, and the seroprevalence of chronic hepatitis B virus (HBV) carriage in children and adolescents in Singapore.

METHODS

The survey involved prospective collection of residual sera from 1,200 children and adolescents aged 1-17 years in two public acute hospitals. Enzyme-linked immunosorbent assays (EIA) or plague reduction neutralisation tests (PRNT) were used to determine the seroprevalence of the vaccine-preventable diseases.

RESULTS

Overall prevalence of measles and rubella antibodies among Singaporean children and adolescents aged 1-17 years were 98.2% (95% CI: 91.2-98.8%) and 94.8% (95% CI: 93.4-95.9%) respectively. 97.1% (95% CI: 96.0-97.9%) of subjects had at least basic protection against diphtheria, while 89.3% (95% CI: 87.5-91.0%) were protected against tetanus. The prevalence of chronic HBV carriage was 0.4% (95% CI: 0.2-1.0%), while 45.7% (95% CI: 42.9-48.5%) were immune against HBV. The seroprevalence for varicella antibodies was 52.9% (95% CI: 50.1-55.7%). Concordance between vaccination status and seroprevalence was observed for measles, rubella, diphtheria and tetanus.

CONCLUSION

Singapore's children and adolescents are well-protected against measles, rubella, diphtheria and tetanus. Continual efforts in ensuring high vaccination coverage should be sustained.

Measles Antibody Levels in Young Infants

BACKGROUND

Infants are often assumed to be immune to measles through maternal antibodies transferred during pregnancy and, in many countries, receive their first measles-containing vaccine at 12 to 15 months. Immunity may wane before this time in measles-eliminated settings, placing infants at risk for measles and complications. We investigated humoral immunity to measles in infants <12 months of age in Ontario, Canada.

METHODS

We selected sera collected at a tertiary pediatric hospital from infants <12 months who were born at ≥37 weeks' gestational age. We excluded infants with conditions that affect antibody levels. We selected ≤25 sera from 8 predetermined age bands and tested them for measles-neutralizing antibody using the plaque-reduction neutralization test. We calculated the proportion immune at each age band, and predictors of infant susceptibility were assessed by using multivariable logistic regression and Poisson regression.

RESULTS

Of 196 infant sera, 56% (110 of 196) were from boys, and 35% (69 of 196) were from infants with underlying medical conditions. In the first month, 20% (5 of 25) of infants had antibodies below the protective threshold, which increased to 92% (22 of 24) by 3 months. By 6 months, all infants had titers below the protective threshold. In a multivariable analysis, infant age was the strongest predictor of susceptibility (odds ratio = 2.13 for each additional month increase; 95% confidence interval: 1.52-2.97).

CONCLUSIONS

Most infants were susceptible to measles by 3 months of age in this elimination setting. Our findings inform important policy discussions relating to the timing of the first dose of measles-containing vaccine and infant postexposure prophylaxis recommendations.

Randomized, double-blinded, controlled non-inferiority trials evaluating the immunogenicity and safety of fractional doses of Yellow Fever vaccines in Kenya and Uganda

Introduction: Yellow fever is endemic in specific regions of sub-Saharan Africa and the Americas, with recent epidemics occurring on both continents. The yellow fever vaccine is effective, affordable and safe, providing life-long immunity following a single dose vaccination. However, the vaccine production process is slow and cannot be readily scaled up during epidemics. This has led the World Health Organization (WHO) to recommend the use of fractional doses as a dose-sparing strategy during epidemics, but there are no randomized controlled trials of fractional yellow fever vaccine doses in Africa. Methods and analysis: We will recruit healthy adult volunteers, adults living with HIV, and children to a series of randomized controlled trials aiming to determine the immunogenicity and safety of fractional vaccine doses in comparison to the standard vaccine dose. The trials will be conducted across two sites; Kilifi, Kenya and Mbarara, Uganda. Recruited participants will be randomized to receive fractional or standard doses of yellow fever vaccine. Scheduled visits will include blood collection for serum and peripheral blood mononuclear cells (PBMCs) before vaccination and on various days - up to 2 years - post-vaccination. The primary outcome is the rate of seroconversion as measured by the plaque reduction neutralization test (PRNT 50) at 28 days post-vaccination. Secondary outcomes include antibody titre changes, longevity of the immune response, safety assessment using clinical data, the nature and magnitude of the cellular immune response and post-vaccination control of viremia by vaccine dose. Ethics and dissemination: The clinical trial protocols have received approval from the relevant institutional ethics and regulatory review committees in Kenya and Uganda, and the WHO Ethics Review Committee. The research findings will be disseminated through open-access publications and presented at relevant conferences and workshops. Registration: ClinicalTrials.gov NCT02991495 (registered on 13 December 2016) and NCT04059471 (registered on 15 August 2019).

Additional Evidence on Serological Correlates of Protection against Measles: An Observational Cohort Study among Once Vaccinated Children Exposed to Measles

To assess correlates of protection against measles and against subclinical measles virus (MV) infection, we recruited once-vaccinated children from geographic regions associated with increased MV circulation and/or at schools with low vaccination coverage in the Netherlands. Paired blood samples were collected shortly after onset of the measles outbreak and after the outbreak. A questionnaire was used to document the likelihood of exposure to MV and occurrence of measles-like symptoms. All blood samples were tested for MV-specific antibodies with five different assays. Correlates of protection were assessed by considering the lowest neutralizing antibody levels in children without MV infection, and by ROC analyses. Among 91 participants, two seronegative children (2%) developed measles, and an additional 19 (23%) experienced subclinical MV infection. The correlate of protection against measles was lower than 0.345 IU/mL. We observed a decreasing attack rate of subclinical MV infection with increasing levels of specific antibodies until 2.1 IU/mL, above which no subclinical MV infections were detected. The ROC analyses found a correlate of protection of 1.71 IU/mL (95% CI 1.01–2.11) for subclinical MV infection. Our correlates of protection were consistent with previous estimates. This information supports the analyses of serosurveys to detect immunity gaps that require targeted intervention strategies.

Calibration and Evaluation of Quantitative Antibody Titers for Varicella-Zoster Virus by Use of the BioPlex 2200

Most commercially available enzyme immunoassay-based methods have limited sensitivity to detect antibody responses to varicella-zoster virus (VZV) in vaccinated individuals, who produce lower antibody levels than those with natural infection. However, more sensitive methods are either not commercially available or less amenable to high-throughput testing.

Most commercially available enzyme immunoassay-based methods have limited sensitivity to detect antibody responses to varicella-zoster virus (VZV) in vaccinated individuals, who produce lower antibody levels than those with natural infection. However, more sensitive methods are either not commercially available or less amenable to high-throughput testing. The BioPlex 2200 measles, mumps, rubella, and varicella (MMRV) IgG assay (Bio-Rad Laboratories, Hercules, CA) is an automated high-throughput platform based on the microsphere Luminex technology that measures antibodies against measles, mumps, rubella, and varicella viruses simultaneously. Although it has U.S. Food and Drug Administration approval as a qualitative diagnostic test for measles, mumps, rubella, and varicella virus immunity, in this study, we have validated the assay to produce quantitative titers (off label) against the VaccZyme VZV glycoprotein (VZVgp) low-level IgG kit (The Binding Site Ltd., Birmingham, UK) using the World Health Organization international standard. Here, we show that the BioPlex 2200 MMRV IgG assay has sensitivity superior to that of the Zeus enzyme-linked immunosorbent assay (ELISA) VZV IgG assay (Zeus Diagnostics, Branchburg, NJ). Using receiver operating characteristic (ROC) analysis and adjusting the cutoff levels, we improved the sensitivity of the quantitative BioPlex 2200 MMRV IgG assay to 97.4%, while maintaining 100% specificity.

Assessment of population immunity to measles in Ontario, Canada: a Canadian Immunization Research Network (CIRN) study

Canada eliminated measles in 1998. We conducted a sero-epidemiology study to estimate population immunity to measles in the province of Ontario, Canada and to identify groups at higher risk of outbreaks. We used a previously developed modified enzyme immunoassay to test 1,199 residual sera from patients aged 1–39 years. We re-tested negative and equivocal sera using a plaque reduction neutralization assay. We interpreted our results in the context of Ontario’s immunization program and vaccine coverage data. Of 1,199 sera, 1035 (86.3%, 95% confidence interval (CI) 84.4, 88.2) were above the measles threshold for protection, 70 (5.8%, 95% CI 4.5, 7.2) were equivocal and 94 (7.8%, 95% CI 6.3, 9.4) were negative. The proportion of positive sera was highest for those 1–5 years, with 180/199 (90.5%, 95% CI 86.4, 94.5) positive sera, and lowest for those age 12–19 years, at 158/199 (79.4%, 95% CI 73.8, 85.0). Adjusted for age, females were more likely than males to have antibody titers above the threshold of protection (odds ratio = 1.60, 95% CI 1.14, 2.24). Most of the study cohort were eligible for two measles vaccine doses, and vaccine uptake in Ontario is >90% for school-aged cohorts. We observed a higher than expected proportion of sera with antibody levels below the threshold of protection, suggesting that immunity in some Ontario age-groups may be waning, despite high vaccine coverage. Alternatively, the traditional measles correlates of protection may not be an appropriate measure of population protection in measles-eliminated settings.

Serum anti-tetanus and measles antibody titres in Ugandan children aged 4 months to 6 years: implications for vaccine programme

To study the antibody response to tetanus toxoid and measles by age following vaccination in children aged 4 months to 6 years in Entebbe, Uganda. Serum samples were obtained from 113 children aged 4-15 months, at the Mother-Child Health Clinic (MCHC), Entebbe Hospital and from 203 of the 206 children aged between 12 and 75 months recruited through the Outpatients Department (OPD). Antibodies to measles were quantified by plaque reduction neutralisation test (PRNT) and with Siemens IgG EIA. VaccZyme IgG EIA was used to quantify anti-tetanus antibodies. Sera from 96 of 113 (85.0%) children attending the MCHC contained Measles PRNT titres below the protective level (120 mIU/ml). Sera from 24 of 203 (11.8%) children attending the OPD contained PRNT titres 0.15 IU/ml by EIA, a level considered protective. The overall concentration of anti-tetanus antibody was sixfold higher in children under 12 months compared with the older children, with geometric mean concentrations of 3.15 IU/ml and 0.49 IU/ml, respectively. For each doubling in age between 4 and 64 months, the anti-tetanus antibody concentration declined by 50%. As time since the administration of the third DTP vaccination doubled, anti-tetanus antibody concentration declined by 39%. The low measles antibody prevalence in the children presenting at the MCHC is consistent with the current measles epidemiology in Uganda, where a significant number of measles cases occur in children under 1 year of age and earlier vaccination may be indicated. The consistent fall in anti-tetanus antibody titre over time following vaccination supports the need for further vaccine boosters at age 4-5 years as recommended by the WHO.

Waning of measles maternal antibody in infants in measles elimination settings - A systematic literature review

INTRODUCTION

Most infants are born with immunity to measles through maternal antibodies transferred in pregnancy, which decay over time. However, in measles elimination settings, where measles does not circulate endemically and most immunity is from immunization rather than infection, maternal antibody levels are lower. This results in infant immunity that wanes earlier, and a wider susceptibility gap between maternal antibody decay and infant immunization than in non-eliminated settings. We aimed to systematically quantify the extent and duration of protection from measles in infants in settings that have sustained measles elimination.

METHODS

We conducted a systematic review of studies of measles maternal antibody waning in infants in measles elimination settings. We searched MEDLINE, Embase, CINAHL, Scopus, BIOSIS Previews, and Global Health databases for relevant studies. Studies were included if they were set in countries that had eliminated measles for ≥3 years, and if the study cohort included healthy, full-term, unvaccinated infants ≤12 months, born to healthy mothers, and reported a relevant measure of measles maternal antibody in infants. We assessed study quality using the MetaQAT tool.

RESULTS

We identified 4692 unique citations, eight of which met inclusion criteria. One study reported anti-measles antibody in cord blood, six reported antibody in infant sera, and one reported both. Two studies reported that 80 and 100% of infants were protected from measles at birth. One study reported no protection amongst 3-7 month old infants, and another reported limited protection in infants >4 months. The remaining studies reported the proportion of infants with detected antibody, but not the proportion immune.

CONCLUSION

Although limited, these data suggest that in settings that have sustained measles elimination, some infants are susceptible to measles well before the age of routine measles immunization. Setting-specific seroprevalence and vaccine effectiveness studies are required to evaluate this in different jurisdictions.

Measles

Measles is a highly contagious disease that results from infection with measles virus and is still responsible for more than 100 000 deaths every year, down from more than 2 million deaths annually before the introduction and widespread use of measles vaccine. Measles virus is transmitted by the respiratory route and illness begins with fever, cough, coryza, and conjunctivitis followed by a characteristic rash. Complications of measles affect most organ systems, with pneumonia accounting for most measles-associated morbidity and mortality. The management of patients with measles includes provision of vitamin A. Measles is best prevented through vaccination, and the major reductions in measles incidence and mortality have renewed interest in regional elimination and global eradication. However, urgent efforts are needed to increase stagnating global coverage with two doses of measles vaccine through advocacy, education, and the strengthening of routine immunisation systems. Use of combined measles-rubella vaccines provides an opportunity to eliminate rubella and congenital rubella syndrome. Ongoing research efforts, including the development of point-of-care diagnostics and microneedle patches, will facilitate progress towards measles elimination and eradication.

Calibration and Evaluation of Quantitative Antibody Titers for Measles Virus by Using the BioPlex 2200

The BioPlex 2200 (Bio-Rad Laboratories, Hercules, CA) is a rapid, automated platform, which can screen large numbers of specimens for antibodies to measles, mumps, rubella, and varicella. Although approved for producing qualitative results, in this study we validated the test (off-label) to allow reporting of quantitative results. To do this, we used the third anti-measles World Health Organization standard to generate a calibration curve that allowed relative fluorescence intensity to be translated into quantitative antibody titer (antibody units [AU]/ml). The results from the BioPlex 2200 and the reference plaque reduction neutralization test (PRNT) exhibited a reasonable correlation following an exponential function, but correlation was poor in low-titer samples. Using a receiver operating characteristics analysis, an equivocal zone for the BioPlex 2200 was established between ≥0.13 and <1.10 AU/ml to achieve 100% specificity (95% confidence interval [CI] = 83.2 to 100%) and 100% sensitivity (95% CI = 93.5 to 100%) versus PRNT. By determining an equivocal range requiring confirmation by PRNT, we can avoid underestimating the levels of immunity through false-negative results and optimize methods for seroepidemiological studies.

A review of testing used in seroprevalence studies on measles and rubella

Seroprevalence studies are an essential tool to monitor the efficacy of vaccination programmes, to understand population immunity and to identify populations at higher risk of infection. An overarching review of all aspects of seroprevalence studies for measles and rubella published between 1998 and June 2014 was undertaken and the findings reported elsewhere. This paper details the considerable variation in the testing formats identified in the review. Apart from serum/plasma samples, testing of oral fluid, breast milk, dry blood spots and capillary whole blood were reported. Numerous different commercial assays were employed, including microtitre plate assays, automated immunoassays and classical haemagglutination inhibition and neutralisation assays. A total of 29 of the 68 (43%) measles and 14 of the 58 (24%) rubella studies reported qualitative test results. Very little information on the testing environment, including quality assurance mechanisms used, was provided. Due to the large numbers of testing systems, the diversity of sample types used and the difficulties in accurate quantification of antibody levels, the results reported in individual studies were not necessarily comparable. Further efforts to standardise seroprevalence studies may overcome this deficiency.

Measles immunity among pregnant women aged 15-44 years in Namibia, 2008 and 2010

Background:

Namibia experienced a large measles outbreak starting in 2009, with 38% of reported cases in adults, including women of reproductive age. Population immunity was assessed among pregnant women to determine whether immunization activities were needed in adults to achieve measles elimination in Namibia.

Methods:

A total of 1708 and 2040 specimens sampled from Namibian pregnant women aged 15–44 years who were included in the 2008 and 2010 National HIV Sentinel Survey, respectively, were tested for measles immunoglobulin G antibody. The proportion of women seropositive overall and by 5-year age strata was determined, and factors associated with seropositivity were analyzed by logistic regression, including age, facility type, gravidity, HIV status, and urban/rural setting. Seropositivity in 2008 versus 2010 was compared.

Results:

In both analysis years, measles seropositivity was lower in 15–19-year-olds (77%) and 20–24-year-olds (85–87%) and higher in 25–44-year-olds (90–94%) (2008, p < 0.001; 2010, p < 0.001). Overall measles seropositivity did not differ between 2008 (87%) and 2010 (87%) (p = 0.7). HIV status did not affect seropositivity.

Conclusions:

Late in a large measles outbreak, 13% of pregnant women in Namibia, and almost one in four 15–19-year-old pregnant women, remained susceptible to measles. In Namibia, immunization campaigns with measles-containing vaccine should be considered for adults.

A randomized, controlled trial of an aerosolized vaccine against measles

BACKGROUND

Aerosolized vaccine can be used as a needle-free method of immunization against measles, a disease that remains a major cause of illness and death. Data on the immunogenicity of aerosolized vaccine against measles in children are inconsistent.

METHODS

We conducted an open-label noninferiority trial involving children 9.0 to 11.9 months of age in India who were eligible to receive a first dose of measles vaccine. Children were randomly assigned to receive a single dose of vaccine by means of either aerosol inhalation or a subcutaneous injection. The primary end points were seropositivity for antibodies against measles and adverse events 91 days after vaccination. The noninferiority margin was 5 percentage points.

RESULTS

A total of 1001 children were assigned to receive aerosolized vaccine, and 1003 children were assigned to receive subcutaneous vaccine; 1956 of all the children (97.6%) were followed to day 91, but outcome data were missing for 331 children because of thawed specimens. In the per-protocol population, data on 1560 of 2004 children (77.8%) could be evaluated. At day 91, a total of 662 of 775 children (85.4%; 95% confidence interval [CI], 82.5 to 88.0) in the aerosol group, as compared with 743 of 785 children (94.6%; 95% CI, 92.7 to 96.1) in the subcutaneous group, were seropositive, a difference of -9.2 percentage points (95% CI, -12.2 to -6.3). Findings were similar in the full-analysis set (673 of 788 children in the aerosol group [85.4%] and 754 of 796 children in the subcutaneous group [94.7%] were seropositive at day 91, a difference of -9.3 percentage points [95% CI, -12.3 to -6.4]) and after multiple imputation of missing results. No serious adverse events were attributable to measles vaccination. Adverse-event profiles were similar in the two groups.

CONCLUSIONS

Aerosolized vaccine against measles was immunogenic, but, at the prespecified margin, the aerosolized vaccine was inferior to the subcutaneous vaccine with respect to the rate of seropositivity. (Funded by the Bill and Melinda Gates Foundation; Measles Aerosol Vaccine Project Clinical Trials Registry-India number, CTRI/2009/091/000673.).

Profiling of measles-specific humoral immunity in individuals following two doses of MMR vaccine using proteome microarrays

INTRODUCTION

Comprehensive evaluation of measles-specific humoral immunity after vaccination is important for determining new and/or additional correlates of vaccine immunogenicity and efficacy.

METHODS

We used a novel proteome microarray technology and statistical modeling to identify factors and models associated with measles-specific functional protective immunity in 150 measles vaccine recipients representing the extremes of neutralizing antibody response after two vaccine doses.

RESULTS

Our findings demonstrate a high seroprevalence of antibodies directed to the measles virus (MV) phosphoprotein (P), nucleoprotein (N), as well as antibodies to the large polymerase (L) protein (fragment 1234 to 1900 AA). Antibodies to these proteins, in addition to anti-F antibodies (and, to a lesser extent, anti-H antibodies), were correlated with neutralizing antibody titer and/or were associated with and predictive of neutralizing antibody response.

CONCLUSION

Our results identify antibodies to specific measles virus proteins and statistical models for monitoring and assessment of measles-specific functional protective immunity in vaccinated individuals.

Estimates of mumps seroprevalence may be influenced by antibody specificity and serologic method

Neutralizing antibodies are assumed to be essential for protection against mumps virus infection, but their measurement is labor- and time-intensive. For this reason, enzyme-linked immunosorbent assays (ELISAs) are typically used to measure mumps-specific IgG levels. However, since there is poor correlation between mumps neutralization titers and ELISAs that measure the presence of mumps-specific IgG levels, ELISAs that better correlate with neutralization are needed. To address this issue, we measured mumps antibody levels by plaque reduction neutralization, by a commercial ELISA (whole-virus antigen), and by ELISAs specific for the mumps nucleoprotein and hemagglutinin. The results indicate that differences in the antibody response to the individual mumps proteins could partially explain the lack of correlation among various serologic tests. Furthermore, the data indicate that some seropositive individuals have low levels of neutralizing antibody. If neutralizing antibody is important for protection, this suggests that previous estimates of immunity based on whole-virus ELISAs may be overstated.

Effect of in-utero HIV exposure and antiretroviral treatment strategies on measles susceptibility and immunogenicity of measles vaccine

INTRODUCTION

The high burden of maternal HIV-infection in sub-Saharan Africa may affect measles control. We evaluated the effect of in-utero HIV-exposure and antiretroviral treatment (ART) strategies on measles antibody kinetics prior and following measles vaccination.

METHODS

Infants aged 6-12 weeks were enrolled. This included HIV-uninfected infants born to HIV-uninfected (HUU) and HIV-infected mothers (HEU). Additionally, we enrolled perinatal HIV-infected infants with CD4% equal or greater than 25% randomized to deferred-ART until clinically or immunologically indicated (Group-3) or immediate-ART initiation (Group-4). Group-4 was further randomized to interrupt ART at 1 year (Group-4a) or 2 years of age (Group-4b). Additionally, a convenience sample of HIV-infected infants with CD4⁺ less than 25% initiated on immediate-ART was enrolled (Group-5). Measles immunoglobulin-G antibodies were quantified by an indirect enzyme immunoassay with titers 330 mIU/ml or more considered 'sero-protective'. The referent group was HUU-children.

RESULTS

The proportion with sero-protective titers at 7.3 weeks of age was higher in HUU (65.2%) compared with any HIV-infected group (range: 16.7-41.8%), but dropped to less than 17% in all groups at age 19.6 weeks. Twenty-eight weeks following the first measles vaccine, Group-4a was less likely to have sero-protective titers (79.3%) as compared to HUU (91.1%; P<0.0001), Group-3 (95.7%; P=0.003) or Group-4b (92.1%; P=0.018). Although the proportion with sero-protective levels were similar between groups immediately postbooster dose, this was lower in HEU (79.6%; P=0.002) and Group-4a (80.3%; P=0.010) compared with HUU (94.3%) 41-weeks later.

CONCLUSION

Greater waning of immunity among HIV-infected children in whom ART was interrupted and in HEU following a booster-dose, indicate the possible need for further measles-booster doses after 2 years of age in these children.

Effect of intermittent preventive treatment for malaria during infancy on serological responses to measles and other vaccines used in the Expanded Programme on Immunization: results from five randomised controlled trials

BACKGROUND

Intermittent preventive treatment for malaria during infancy (IPTi) is the administration of a full therapeutic course of antimalarial drugs to infants living in settings where malaria is endemic, at the time of routine vaccination in the first year of life. We investigated whether IPTi with sulfadoxine-pyrimethamine or other antimalarial drug combinations adversely affected serological responses to vaccines used in the Expanded Programme on Immunization (EPI).

METHODS

The study was done in a subset of children enrolled in five randomised controlled trials in Navrongo, Ghana; Kilimanjaro, Tanzania; Manhica, Mozambique; Kisumu, Kenya; and Bungoma, Kenya. All infants presenting for the second dose of the diphtheria-tetanus-pertussis vaccination (given at 8-10 weeks of age) were eligible, and analyses included all children who had received measles vaccination (at 9 months of age) and at least one dose of IPTi or placebo. Blood samples were collected before and after vaccination, and antibody titres were measured by plaque reduction neutralisation (measles, yellow fever), microneutralisation (polio serotypes 1 and 3), and ELISA (all other EPI antigens). Laboratory personnel were unaware of the randomisation groups. We compared the proportion of infants in the IPTi and placebo groups who did not attain protective antibody titres after vaccination, using a one-sided significance non-inferiority margin of 5% for measles (the primary endpoint) and 10% for other EPI antigens.

FINDINGS

Between September, 2000, and May, 2008, 8416 children were enrolled in the five studies. Paired samples from 2368 children from sites where sulfadoxine-pyrimethamine was compared with placebo were analysed for measles antibodies. 464 children with detectable measles antibody in their sample before vaccination were excluded, leaving 1904 individuals (934 placebo and 970 sulfadoxine-pyrimethamine) in the study. IPTi with sulfadoxine-pyrimethamine did not have a clinically significant effect on immune responses to measles vaccine; 61 of 970 (6·3%) children who received IPTi did not develop a protective antibody response after measles vaccination compared with 60 of 934 (6·4%) who received placebo, a difference of -0·14% (95% CI -2·3 to 2·1). When other antimalarial drugs were used for IPTi the results were much the same. Among 2396 children from whom serological response data for other EPI antigens were available, we identified no evidence of an adverse effect of IPTi with sulfadoxine-pyrimethamine or other antimalarial drugs on the proportion achieving protective antibody concentrations.

INTERPRETATION

IPTi with sulfadoxine-pyrimethamine does not affect serological responses to EPI vaccines. This analysis, therefore, supports the WHO recommendation for coadministration of IPTi with sulfadoxine-pyrimethamine to infants at the time of the second and third doses of DTP and measles vaccination, in areas of sub-Saharan Africa with moderate to high malaria transmission and where malaria parasites are sensitive to these drugs. It also suggests that treatment of clinical malaria at or around the time of vaccination does not compromise vaccine responsiveness.

FUNDING

Bill & Melinda Gates Foundation.

Seroprevalence of measles among children affected by national measles elimination program in Korea, 2010

BACKGROUND

Following the implementation of national measles elimination plan in Korea, the elimination was declared in 2006. In order to sustain the elimination, high population immunity should be continuously monitored. To evaluate the current age-related susceptibility within the Korean population, we conducted the seroprevalence in children and adolescents who were affected by the national measles elimination plan.

METHODS

We used residual serum specimens to measure measles specific IgG and geometric mean titer (GMT) in birth cohorts 2007-2008 and 1997-2003. Among birth cohorts, 2007-2008 cohorts were grouped to evaluate the timeliness of first dose of MMR, 1994-2003 cohorts were grouped to evaluate the effect of keep-up MMR2 campaign, and 1992-1993 cohorts were grouped to evaluate the effect of catch-up campaign in 2001.

RESULTS

Overall, measles seropositivity rate was 86%. The highest seroprevalence of measles IgG was in birth cohorts 2007-2008. Measles seropositivity declined continuously in age groups. The birth cohorts 1994-1996 showed significantly lower levels of seropositivity and GMT than did the other birth cohorts.

CONCLUSION

Despite efforts to eliminate measles for the past 10 years in Korea, our study revealed specific birth cohorts remaining at risk for transmission. The adolescents born during 1994-1996 had the lowest measles seropositivity levels, and might represent a 'pocket' that has potential at increased risk for measles transmission. Further discussion for follow-up immunization should be placed for consideration in the near future.

Long-term safety and serologic response to measles, mumps, and rubella vaccination in HIV-1 infected adults

We analyzed HIV viral load (VL) and CD4 count changes, and antibody responses following MMR vaccination of individuals in the U.S. Military HIV Natural History Study cohort. Cases receiving at least one dose of MMR vaccine after HIV diagnosis were matched 1:2 to HIV-positive controls not receiving the vaccine. Baseline was defined as time of vaccination for cases and indexed and matched to the time post-HIV diagnosis for controls. Changes in CD4 count and VL at 6, 12, 18 and 24 months were compared between cases and controls using a general linear model. Available sera from cases were tested for MMR seropositivity at baseline and post-vaccination at 6, 12, 18, and 24 months. Overall mean CD4 count change from baseline through 24 months was 20 (±23) cells/μL greater for cases than controls (p=0.39). Similar non-significant changes in CD4 cell count were seen in the subset of those not on HAART at baseline. VL changes were small and similar between groups (mean differential change -0.04 (±0.18) log(10) copies/mL; p=0.84). Of 21 vaccinated participants with baseline serologic testing, 14 (67%) were reactive to measles, 19 (91%) to mumps, and 20 (95%) to rubella. Three (43%) of 7 participants nonreactive to measles developed measles IgG; for mumps, 1 (50%) of 2 developed mumps IgG; for rubella, 1 (100%) developed rubella IgG. MMR vaccination did not result in detrimental immunologic or virologic changes through 24 months post-vaccination.