Nationwide measles epidemic in Ukraine: The effect of low vaccine effectiveness

Evolving measles status and immunization policy development in six European countries

Developing and implementing new immunization policies in response to shifting epidemiology is a critical public health component. We adopted a mixed-methods approach (via narrative literature review [101 articles] and 9 semi-structured interviews) to evaluate policy development in response to shifting measles epidemiology in six European countries (Italy, Belgium, Germany, Romania, UK, and Ukraine); where policies and strategies have evolved in response to country-specific disease and vaccination patterns. Periodic outbreaks have occurred in all countries against a background of declining measles-containing-vaccine (MCV) uptake and increasing public vaccine hesitancy (with substantial regional or social differences in measles burden and vaccine uptake). Health-care worker (HCW) vaccine skepticism is also seen. While many outbreaks arise or involve specific susceptible populations (e.g., minority/migrant communities), the broader pattern is spread to the wider (and generally older) population; often among incompletely/non-vaccinated individuals as a legacy of previous low uptake. Immunization policy and strategic responses are influenced by political and social factors, where public mistrust contributes to vaccine hesitancy. A strong centralized immunization framework (allied with effective regional implementation and coherent political commitment) can effectively increase uptake. Mandatory vaccination has increased childhood MCV uptake in Italy, and similar benefits could be anticipated for other countries considering vaccine mandates. Although possible elsewhere, socio-political considerations render mandating impractical in other countries, where targeted immunization activities to bolster routine uptake are more important. Addressing HCW skepticism, knowledge gaps, improving access and increasing public/community engagement and education to address vaccine hesitancy/mistrust (especially in communities with specific unmet needs) is critical.

Challenges to Achieving Measles Elimination, Georgia, 2013-2018

Controlling measles outbreaks in the country of Georgia and throughout Europe is crucial for achieving the measles elimination goal for the World Health Organization’s European Region. However, large-scale measles outbreaks occurred in Georgia during 2013–2015 and 2017–2018. The epidemiology of these outbreaks indicates widespread circulation and genetic diversity of measles viruses and reveals persistent gaps in population immunity across a wide age range that have not been sufficiently addressed thus far. Historic problems and recent challenges with the immunization program contributed to outbreaks. Addressing population susceptibility across all age groups is needed urgently. However, conducting large-scale mass immunization campaigns under the current health system is not feasible, so more selective response strategies are being implemented. Lessons from the measles outbreaks in Georgia could be useful for other countries that have immunization programs facing challenges related to health-system transitions and the presence of age cohorts with historically low immunization coverage.

Measles and rubella serosusceptibity among population vaccinated with different schedules: the potential impact on measles-rubella elimination in Iran

BACKGROUND

Iranian children were vaccinated with the scheduled two doses of monovalent measles vaccine (mMV) from 1984. In December 2003, a nationwide campaign of measles-rubella (MR) immunization was established to vaccinate 5-25 year- old individuals. In 2004, the mMV was replaced with measles- mumps- rubella (MMR) vaccine. Despite the high vaccination coverage, the outbreaks of measles still occur in the country. In this Study, the MR immunity status of various age groups, vaccinated with different schedules was investigated, and the immunologic response of seronegative subjects to revaccination was examined.

METHODS

This cross-sectional study was conducted among 7-33-year-old healthy individuals with a documented history of measles vaccination from November 2017 to June 2018. The subjects were categorized as follows: group A, including 20-33 year-old individuals; vaccinated with 1-2 doses of mMV at ages 9 and 15 months, and revaccinated with MR, group B, including 15-19-year-old individuals, vaccinated with two doses of mMV at 9 and 15 months of age, and received additional dose of MMR upon school entrance, group C, including 11-14 year-old individuals, vaccinated with two-doses of MMR at the ages of 15 months and 6 years, and group D, including 7-10 year-old individuals vaccinated with two-doses of MMR vaccine at the ages 12 and 18 months, respectively. Levels of antimeasles- antirubella IgG antibodies in the collected sera were measured. Also antimeasles- antirubella IgM and IgG of seronegative individuals were reexamined at 4-6 weeks after MMR revaccination. The collected data were analyzed using descriptive statistical methods.

RESULTS

A total of 635 individuals were investigated in this study. Group A, 98; group B, 295; group C, 139; and group D, 103 persons. Overall, 12.3 and 18.4% of the population were seronegative for measles and rubella antibodies. This rate varied greatly between the 4 groups: group A, 0/0-2%; group B,15.2-25.0%; group C,11.5-17.2%; and groupD,14.6-18.4%. After revaccination, 92 and 94.9% of seronegative individuals showed IgG response to measles and rubella vaccines, respectively.

CONCLUSION

Despite the high coverage rate of M-R containing vaccines, a significant number of vaccinated subjects were seronegative for measles and rubella, possibly because of secondary vaccine failure; this may negatively affect measles-rubella elimination targets in the country. If these findings are confirmed in similar future studies, a more robust regional/national supplementary immunization activity will be considered.

The effect of time since measles vaccination and age at first dose on measles vaccine effectiveness - A systematic review

BACKGROUND

In settings where measles has been eliminated, vaccine-derived immunity may in theory wane more rapidly due to a lack of immune boosting by circulating measles virus. We aimed to assess whether measles vaccine effectiveness (VE) waned over time, and if so, whether differentially in measles-eliminated and measles-endemic settings.

METHODS

We performed a systematic literature review of studies that reported VE and time since vaccination with measles-containing vaccine (MCV). We extracted information on case definition (clinical symptoms and/or laboratory diagnosis), method of vaccination status ascertainment (medical record or vaccine registry), as well as any biases which may have arisen from cold chain issues and a lack of an age at first dose of MCV. We then used linear regression to evaluate VE as a function of age at first dose of MCV and time since MCV.

RESULTS

After screening 14,782 citations, we identified three full-text articles from measles-eliminated settings and 33 articles from measles-endemic settings. In elimination settings, two-dose VE estimates increased as age at first dose of MCV increased and decreased as time since MCV increased; however, the small number of studies available limited interpretation. In measles-endemic settings, one-dose VE increased by 1.5% (95% CI 0.5, 2.5) for every month increase in age at first dose of MCV. We found no evidence of waning VE in endemic settings.

CONCLUSIONS

The paucity of data from measles-eliminated settings indicates that additional studies and approaches (such as studies using proxies including laboratory correlates of protection) are needed to answer the question of whether VE in measles-eliminated settings wanes. Age at first dose of MCV was the most important factor in determining VE. More VE studies need to be conducted in elimination settings, and standards should be developed for information collected and reported in such studies.

Outbreak of measles among persons with secondary vaccine failure, China, 2018

Although the incidence of measles has been dramatically reduced by the highly effective measles vaccine, cases of measles and outbreaks continue to occur in vaccinated population because of immunization failure. We report on an outbreak in which two cases had previous evidence of measles immunity and then one of them transmitted measles infection to an unvaccinated contact. The cases and contacts exposed during the outbreak were investigated. Clinical information and epidemiological information were obtained. Serum samples were collected for measles-specific immunoglobulin M (IgM), immunoglobulin G (IgG) and IgG avidity. Throat swabs were obtained to test for measles virus RNA. Two measles cases (case 1 and case 2) who have received one dose of MCV in past 5 years, and both working at a hospital in Beijing, occurred in 18th and 20nd of January, respectively. Out of the 102 contacts, one additional case (case 3) who had a close, long-term co-exposure with case 1 was reported subsequently. No additional cases of measles occurred among 15 contacts of case 3. The index case was not ascertained through the outbreak review. All three cases had laboratory confirmation of measles infection. Both case 1 and case 2 had high-avidity IgG antibody characteristic of a secondary immune response and developed a modified clinical presentation. This report confirms that a vaccinated individual with documented secondary vaccine failure (SVF) could transmit measles and is the second report since a New York City outbreak (the first report in China). The outbreak represented a series of rare events, so we can conclude that the SVF individuals in the transmission chain of measles are unlikely to threaten measles elimination. The importance of the herd immunity in preventing transmission and sensitive surveillance activities in case of misdiagnosis is emphasized.

Measles and rubella seroimmunity in newly arrived adult immigrants in Sweden

BACKGROUND

International migrants could be considered as a risk group for being susceptible to vaccine preventable diseases such as measles and rubella. However, data on immunity in different migrant groups are scarce. Apart from asylum seekers and refugees, other immigrant groups might also be at risk. We have examined measles and rubella specific IgG antibodies among newly arrived adult immigrants in Skåne region in southern Sweden. In contrast to children, adult immigrants are not offered catch-up vaccinations after arrival.

METHODS

Stored serum samples from 989 asylum seekers and 984 pregnant women from the antenatal screening program, who had recently settled in Sweden, were analyzed for specific measles and rubella IgG-antibodies. Sex, age, reason for screening and geographic origin were variables entered into a multivariate regression model.

RESULTS

There were considerable differences in seroimmunity to measles with regard to geographic origin (44-97%). Measles seroimmunity gaps were most prominent in immigrants from some European regions such as the Baltic countries, the former Yugoslavia and the Newly Independent States and Russia. Seroprotection for rubella varied less between geographic regions (90-99%).

CONCLUSION

Susceptibility to measles among adult immigrants arriving in Sweden varies considerably depending on their geographic origin. Vaccinations against measles and rubella should be offered to groups of immigrants who might be incompletely immunized.

Risk Factors for Measles Virus Infection Among Adults During a Large Outbreak in Postelimination Era in Mongolia, 2015

Background

In 2015, a large nationwide measles outbreak occurred in Mongolia, with very high incidence in the capital city of Ulaanbaatar and among young adults.

Methods

We conducted an outbreak investigation including a matched case-control study of risk factors for laboratory-confirmed measles among young adults living in Ulaanbaatar. Young adults with laboratory-confirmed measles, living in the capital city of Ulaanbaatar, were matched with 2-3 neighborhood controls. Conditional logistic regression was used to estimate adjusted matched odds ratios (aMORs) for risk factors, with 95% confidence intervals.

Results

During March 1-September 30, 2015, 20 077 suspected measles cases were reported; 14 010 cases were confirmed. Independent risk factors for measles included being unvaccinated (adjusted matched odds ratio [aMOR] 2.0, P < .01), being a high school graduate without college education (aMOR 2.6, P < .01), remaining in Ulaanbaatar during the outbreak (aMOR 2.5, P < .01), exposure to an inpatient healthcare facility (aMOR 4.5 P < .01), and being born outside of Ulaanbaatar (aMOR 1.8, P = .02).

Conclusions

This large, nationwide outbreak shortly after verification of elimination had high incidence among young adults, particularly those born outside the national capital. In addition, findings indicated that nosocomial transmission within health facilities helped amplify the outbreak.

Synthesis of Evidence to Characterize National Measles and Rubella Exposure and Immunization Histories

Population immunity depends on the dynamic levels of immunization coverage that countries achieve over time and any transmission of viruses that occur within the population that induce immunity. In the context of developing a dynamic transmission model for measles and rubella to support analyses of future immunization policy options, we assessed the model inputs required to reproduce past behavior and to provide some confidence about model performance at the national level. We reviewed the data available from the World Health Organization (WHO) and existing measles and rubella literature for evidence of historical reported routine and supplemental immunization activities and reported cases and outbreaks. We constructed model input profiles for 180 WHO member states and three other areas to support disease transmission model development and calibration. The profiles demonstrate the significant variability in immunization strategies used historically by regions and member states and the epidemiological implications of these historical choices. The profiles provide a historical perspective on measles and rubella immunization globally at the national level, and they may help immunization program managers identify existing immunity and/or knowledge gaps.

An assessment of measles vaccine effectiveness, Australia, 2006-2012

OBJECTIVE

Vaccine effectiveness analysis serves as a critical evaluation for immunization programmes and vaccination coverage. It also contributes to maintaining public confidence with the vaccine providers. This study estimated measles vaccine effectiveness at the population level using Australian national notifications data between 2006 and 2012.

METHODS

Notification data were obtained from the National Notifiable Diseases Surveillance System. Vaccination status was classified according to whether a case had received zero, one or two doses of measles-containing vaccine. Cases aged less than 1 year and those with unknown vaccination status were excluded. All children with disease onset between 1 January 2006 and 31 December 2012 who were born after 1996 were included. Cases were matched to controls extracted from the Australian Childhood Immunization Register according to date of birth and jurisdiction of residence. Vaccine effectiveness was estimated by conditional logistic regression. Sensitivity analyses were conducted to test data robustness.

RESULTS

Vaccine effectiveness was estimated at 96.7% (95% confidence interval [CI]: 94.5-98.0%) for one dose and 99.7% (95% CI: 99.2-99.9%) for two doses of measles vaccine. For at least one dose, effectiveness was estimated at 98.7% (95% CI: 97.9-99.2%). Sensitivity analyses did not significantly alter the base estimates.

DISCUSSION

Vaccine effectiveness estimates suggested that the measles vaccine was protective at the population level between 2006 and 2012. However, vaccination coverage gaps may have contributed to recent measles outbreaks and may represent a serious barrier for Australia to maintain measles elimination status.

Vaccination in elite athletes

Public health vaccination guidelines cannot be easily transferred to elite athletes. An enhanced benefit from preventing even mild diseases is obvious but stronger interference from otherwise minor side effects has to be considered as well. Thus, special vaccination guidelines for adult elite athletes are required. In most of them, protection should be strived for against tetanus, diphtheria, pertussis, influenza, hepatitis A, hepatitis B, measles, mumps and varicella. When living or traveling to endemic areas, the athletes should be immune against tick-borne encephalitis, yellow fever, Japanese encephalitis, poliomyelitis, typhoid fever, and meningococcal disease. Vaccination against pneumococci and Haemophilus influenzae type b is only relevant in athletes with certain underlying disorders. Rubella and papillomavirus vaccination might be considered after an individual risk–benefit analysis. Other vaccinations such as cholera, rabies, herpes zoster, and Bacille Calmette–Guérin (BCG) cannot be universally recommended for athletes at present. Only for a very few diseases, a determination of antibody titers is reasonable to avoid unnecessary vaccinations or to control efficacy of an individual’s vaccination (especially for measles, mumps, rubella, varicella, hepatitis B and, partly, hepatitis A). Vaccinations should be scheduled in a way that possible side effects are least likely to occur in periods of competition. Typically, vaccinations are well tolerated by elite athletes, and resulting antibody titers are not different from the general population. Side effects might be reduced by an optimal selection of vaccines and an appropriate technique of administration. Very few discipline-specific considerations apply to an athlete’s vaccination schedule mainly from the competition and training pattern as well as from the typical geographical distribution of competitive sites.

Etiology of maculopapular rash in measles and rubella suspected patients from Belarus

As a result of successful implementation of the measles/rubella elimination program, the etiology of more and more double negative cases remains elusive. The present study determined the role of different viruses as causative agents in measles or rubella suspected cases in Belarus. A total of 856 sera sent to the WHO National Laboratory between 2009 and 2011 were tested for specific IgM antibodies to measles virus (MV), rubella virus (RV) and human parvovirus B19 (B19V). The negatives were further investigated for antibodies to enterovirus (EV) and adenovirus (AdV). Children of up to 3 years were tested for IgM antibodies to human herpesvirus 6 (HHV6). A viral etiology was identified in 451 (52.7%) cases, with 6.1% of the samples being positive for MV; 2.6% for RV; 26.2% for B19V; 9.7% for EV; 4.6% for AdV; and 3.6% for HHV6. Almost all measles and rubella cases occurred during limited outbreaks in 2011 and nearly all patients were at least 15 years old. B19V, EV and AdV infections were prevalent both in children and adults and were found throughout the 3 years. B19V occurred mainly in 3-10 years old children and 20-29 years old adults. EV infection was most common in children up to 6 years of age and AdV was confirmed mainly in 3-6 years old children. HHV6 infection was mostly detected in 6-11 months old infants. Laboratory investigation of measles/rubella suspected cases also for B19V, EV, AdV and HHV6 allows diagnosing more than half of all cases, thus strengthening rash/fever disease surveillance in Belarus.

Difficulties in eliminating measles and controlling rubella and mumps: a cross-sectional study of a first measles and rubella vaccination and a second measles, mumps, and rubella vaccination

Background

The reported coverage of the measles–rubella (MR) or measles–mumps–rubella (MMR) vaccine is greater than 99.0% in Zhejiang province. However, the incidence of measles, mumps, and rubella remains high. In this study, we assessed MMR seropositivity and disease distribution by age on the basis of the current vaccination program, wherein the first dose of MR is administered at 8 months and the second dose of MMR is administered at 18–24 months.

Methods

Cross-sectional serological surveys of MMR antibodies were conducted by collecting epidemiological data in Zhejiang province, China in 2011. In total, 1015 participants were randomly selected from two surveillance sites. Serum MMR-specific immunoglobulin G levels were tested by enzyme-linked immunosorbent assay. The geometric mean titers and seroprevalence with 95% confidence intervals (CIs) were calculated by age and gender. Proportions of different dose of vaccine by age by vaccine were also identified. Statistically significant differences between categories were assessed by the Chi-square test.

Results

Over 95% seroprevalence rates of measles were seen in all age groups except <7 months infants. Children aged 5–9 years were shown lower seropositivity rates of mumps while elder adolescences and young adults were presented lower rubella seroprevalence. Especially, rubella seropositivity was significantly lower in female adults than in male. Nine measles cases were unvaccinated or unknown vaccination history. Among them, 66.67% (6/9) patients were aged 20–29 years while 33.33% (3/9) were infants aged 8–12 months. In addition, 57.75% (648/1122) patients with mumps were children aged 5–9 years, and 50.54% (94/186) rubella cases were aged 15–39 years.

Conclusions

A timely two-dose MMR vaccination schedule is recommended, with the first dose at 8 months and the second dose at 18–24 months. An MR vaccination speed-up campaign may be necessary for elder adolescents and young adults, particularly young females.

Measles epidemic from 1951 to 2012 and vaccine effectiveness in Guangzhou, southern China

BACKGROUND

Since the National Expanded Program on Immunization was implemented in China, considerable progress has been made in reducing the incidence of measles. However, the incidence of measles increased again in 2004. Few post-marketing studies on measles vaccine effectiveness were reported in China. In this study, we aimed to describe the measles epidemic and to evaluate the effectiveness of the measles vaccine in Guangzhou, southern China.

METHODS

Based on the surveillance data for measles, we investigated the epidemiology during different periods between 1951 and 2012. We analyzed the clinical characteristics of laboratory-confirmed cases of measles between 2009 and 2012 and conducted a case-control study using test-negative cases as controls. We determined the protective effect of measles vaccine.

RESULTS

The highest annual incidence in Guangzhou was 2187.15/100,000 in 1964, and the lowest was 0.32/100,000 in 2011. The average incidence of measles from 1951 to 2012 was 306.27/100,000. There was a significant tendency of decline in recent years. From 2009 to 2012, there are 700 laboratory-confirmed cases were reported with an average onset age of 2.5 (median) years. The non-vaccinated target population (age<8 months and ≥ 15 years) accounted for 56.7% of the cases. The transient (non-resident) population accounted for 51.3% of the cases. Fewer cases were observed in the population targeted for measles vaccine (aged 8 months to 14 years). The effectiveness of a single dose of the measles vaccine was 89.1% (95% confidence interval (CI), 44.5-97.9), and the effectiveness of ≥ 2 doses of the measles vaccine was 97.8% (95% CI, 88.3-99.6) in children aged 8 months to 14 years old.

CONCLUSIONS

There is a significant overall decline in the incidence of measles (including clinical and laboratory confirmed cases) in the measles vaccine targeted population in Guangzhou. Two doses of measles vaccine are more effective than one dose in preventing measles in China. In order to accelerate the elimination of measles, vaccination should also be given to the transient and the non-vaccine targeted population.

[Progress in the elimination of measles and rubella in the WHO European Region]

Substantial progress has been made in the World Health Organization (WHO) European Region toward reaching the goal of measles and rubella elimination. We analyzed the surveillance data of 2012 on measles and rubella for age-group, diagnosis confirmation status (clinical, laboratory-confirmed and epidemiologically linked), vaccination status, and measles-related deaths. For 2012, there were 23,871 measles cases and 29,361 rubella cases reported in the region, mostly among unvaccinated persons. Almost one in three patients with measles and one in five patients with rubella were aged 20 years and older. In a few countries, widespread outbreaks or indigenous transmission of measles persisted in 2012. While most countries in the region have controlled rubella, a small number still reported a high incidence and several outbreaks. Therefore, more efforts are required to achieve the goal of eliminating measles and rubella in the WHO European Region by 2015, particularly in high-incidence countries. The WHO measles and rubella elimination plan stipulates that all countries should achieve and maintain the required high vaccination coverage while conducting high-quality surveillance.

Higher risk of measles when the first dose of a 2-dose schedule of measles vaccine is given at 12-14 months versus 15 months of age

BACKGROUND

In 2011, >750 cases of measles were reported in Quebec, Canada, where a routine 2-dose measles immunization schedule, in which measles vaccine is given at 12 and 18 months of age, had been in effect since 1996. Effectiveness of this schedule was assessed during a high school outbreak.

METHODS

Cases were identified by passive followed by active surveillance. Classical cases met the national surveillance definition; attenuated cases showed clinical signs and high measles-specific immunoglobulin G but did not fulfill all classical criteria. Immunization status was ascertained from written records, and vaccine effectiveness (VE) was calculated as 1 - [(risk of measles in vaccinated individuals)/(risk in unvaccinated individuals)] × 100%.

RESULTS

Among 1306 students, 110 measles cases were identified; 98 were classical cases, and 12 were attenuated cases. The attack rates among unvaccinated and fully vaccinated students were 82% and 4.8%, respectively. The VE among 2-dose recipients was 95.5% against classical and 94.2% against all (classical + attenuated) measles. Among 2-dose recipients, attack rates with first immunization at 12 and ≥15 months of age were 5.8% and 2.0%, respectively, with corresponding VE values of 93.0% and 97.5%. The risk of measles in 2-dose recipients was significantly (3-4-fold) higher when vaccine was first administered at 12 months of age, compared with ≥15 months of age (P = .04).

CONCLUSIONS

Despite compliance with the recommended 2-dose measles immunization schedule, 6% of high school students were susceptible during this outbreak. Residual susceptibility was 2-4-fold higher among 2-dose recipients who had received the first dose of vaccine prior to 15 months of age. If confirmed in other settings, these results suggest that administration of the first dose of measles vaccine before 15 months of age may not be optimal for measles elimination efforts.

Spread of measles virus D4-Hamburg, Europe, 2008-2011

A new strain of measles virus, D4-Hamburg, was imported from London to Hamburg in December 2008 and subsequently spread to Bulgaria, where an outbreak of >24,300 cases was observed. We analyzed spread of the virus to demonstrate the importance of addressing hard-to-reach communities within the World Health Organization European Region regarding access to medical care and vaccination campaigns. The D4-Hamburg strain appeared during 2009-2011 in Poland, Ireland, Northern Ireland, Austria, Greece, Romania, Turkey, Macedonia, Serbia, Switzerland, and Belgium and was repeatedly reimported to Germany. The strain was present in Europe for >27 months and led to >25,000 cases in 12 countries. Spread of the virus was prevalently but not exclusively associated with travel by persons in the Roma ethnic group; because this travel extends beyond the borders of any European country, measures to prevent the spread of measles should be implemented by the region as a whole.

Laboratory characterization of measles virus infection in previously vaccinated and unvaccinated individuals

Waning immunity or secondary vaccine failure (SVF) has been anticipated by some as a challenge to global measles elimination efforts. Although such cases are infrequent, measles virus (MeV) infection can occur in vaccinated individuals following intense and/or prolonged exposure to an infected individual and may present as a modified illness that is unrecognizable as measles outside of the context of a measles outbreak. The immunoglobulin M response in previously vaccinated individuals may be nominal or fleeting, and viral replication may be limited. As global elimination proceeds, additional methods for confirming modified measles cases may be needed to understand whether SVF cases contribute to continued measles virus (MeV) transmission. In this report, we describe clinical symptoms and laboratory results for unvaccinated individuals with acute measles and individuals with SVF identified during MeV outbreaks. SVF cases were characterized by the serological parameters of high-avidity antibodies and distinctively high levels of neutralizing antibody. These parameters may represent useful biomarkers for classification of SVF cases that previously could not be confirmed as such using routine laboratory diagnostic techniques.

Low measles seropositivity rate among children and young adults: a sero-epidemiological study in southern China in 2008

To obtain sero-epidemiological profile and develop optimal strategies to promote measles elimination, we conducted a measles seroprevalence study using stratified sampling method in Guangzhou, southern China in 2008. 4036 samples were analyzed by the enzyme-linked immunosorbent assay method and the overall sero-positive rate of measles antibody was 70.6% (95% CI 69.2-72.0%). Positive seroprevalences differed among age groups (P=0.000) and a W-curve distribution was observed. The 15-29 years group had the low positive rate of 58.8% (95% CI 54.9-62.7%). Catch-up vaccination campaigns should be promoted among susceptible population of ≤ 29 year olds including women of childbearing age.

Enhanced surveillance for measles in low-incidence territories of the Russian Federation: defining a rate for suspected case investigation

The rate of case investigation for measles-like illness (MLI) is an important indicator for the quality of measles surveillance in countries targeting measles elimination. However, a benchmark rate is still being discussed. We assessed different rates of investigation in 11 territories of the Russian Federation with low reported measles incidence during the previous 4-7 years. Each territory maintained their existing surveillance activities and also undertook additional surveillance activities for MLI over a 3-year period. The annual routine rate of investigation varied from 0·06 to 1·8/100,000 population; the overall rate of investigation, including enhanced surveillance, varied from 1·4 to 7·2/100,000. Forty-nine (30·8%) of 159 measles cases detected were identified through enhanced surveillance. Based on the results of this study, the Russian Federation concluded that a rate of routine investigation of 2/100,000 provided the best balance between available resources and sensitivity for detection of measles cases.

Relaxation of purifying selection on live attenuated vaccine strains of the family Paramyxoviridae

In wild-type sequences of three paramyxoviruses (measles virus, mumps virus, and Newcastle disease virus), nucleotide diversity at both non-coding sites and at nonsynonymous sites in coding regions was significantly reduced in comparison to that at synonymous sites. Likewise, both the mean and variance of gene diversity at nonsynonymous polymorphic sites were reduced in comparison to non-coding and synonymous sites. Neither of these patterns, which reflect the action of purifying selection against deleterious mutations at nonsynonymous and non-coding sites, were seen in the case of live attenuated vaccine strains, implying that purifying selection has been substantially relaxed on the latter, potentially affecting their biological properties, including antigenicity and vaccine effectiveness. Since the accumulation of mutations increases as a function of the number of generations of replication, these findings highlight the utility of minimizing the number of generations between the original vaccine master seed and the strains used in vaccination, along with periodic monitoring of the extent of sequence evolution.