Direct sequencing of measles virus complete genomes in the midst of a large-scale outbreak

Case Ascertainment of Measles during a Large Outbreak-Laboratory Compared to Epidemiological Confirmation

Measles is a highly contagious viral disease, and hence, sufficient herd immunity is obligatory to prevent infection transmission. Measles is still a cause of considerable disease burden globally, mainly in children. During a national measles outbreak in Israel in 2018-2019, the peak incidence rates occurred in the Jerusalem district. Most measles cases in the Jerusalem district (75.5%, 1702) were observed in children younger than 15 years of age, 49.2% (1109) were in children under 5 years of age, and 18.9% (425) were in infants under 1 year of age. The routine measles vaccination schedule includes two doses at 1 and 6 years of age. Most cases (1828, 81.1%) were unvaccinated (zero measles vaccine doses). These cases comprised the 425 affected infants under 1 year of age, who were ineligible for vaccination, along with the 1403 children over 1 year of age, who were otherwise unvaccinated. This study aimed to describe the epidemiologic and laboratory features of this measles outbreak, and to investigate case ascertainment (laboratory confirmed compared to epidemiologically confirmed cases). The study population included 2254 measles cases notified during the period spanning June 2018 to May 2019 in the Jerusalem district (incidence rate 176 per 10,000 population). Of the 2254 cases, 716 (31.8%) were laboratory confirmed, and 1538 (68.2%) were confirmed as epidemiologically linked. Most laboratory confirmed cases (420, 58.7%) underwent real-time PCR tests. Serological tests (measles IgM and IgG) were used in 189 (26.4%) cases, and a combination of RT-PCR and serology was used in 107 (14.9%) cases. In a multivariate model analysis, the variables significantly associated (after adjustment) with higher odds for laboratory confirmation included month of disease onset (late), additional measles cases in the household (single case), place of medical treatment (hospital; either emergency department, or hospitalization) and vaccination status (at least one prior vaccine dose). The measles outbreak described demonstrates the urgency of addressing vaccination gaps with appropriate outbreak prevention programs. The road to measles elimination needs to be paved with robust public health infrastructure, excellent field epidemiology for outbreak surveillance, investigation, and control, and laboratory proficiency.

Rapid molecular epidemiology investigations into two recent measles outbreaks in Israel detected from October 2023 to January 2024

Between late 2023 and early 2024, two measles outbreaks occurred in Israel, each caused by importation of measles virus strains of respective B3 and D8 genotypes. In this study, we validate transmission pathways uncovered by epidemiological investigations using a rapid molecular approach, based on complete measles virus genomes. The presented findings support this rapid molecular approach in complementing conventional contact tracing and highlight its potential for informing public health interventions.

Measles clinical presentation, hospitalization and vaccination status among children in a community-wide outbreak

BACKGROUND

In 2018-2019, a measles outbreak emerged in Israel (4158 notified cases). We aimed to evaluate the measles characteristics and the vaccination status among children during the outbreak.

METHODS

We performed a cross-sectional study of measles cases in children under 18 years, residing in the Jerusalem district (2254 notified measles cases, June 2018-May 2019). The variables included: clinical symptoms (fever, rash, cough, coryza, conjunctivitis), hospitalizations and child's vaccination status. The national measles vaccination schedule includes two vaccine doses (at ages 12 months and 6 years).

RESULTS

Children, under 18 years, comprised 79% (1782/2254) of the notified measles cases. The hospitalization rate was 6.6%. There was one fatality. The measles vaccination status was analyzed by age groups. Infants under 12 months (n = 425) were excluded. Children aged 1-5 years (n = 785) and 6-17 years (n = 572) were expected to receive 1 and 2 measles vaccine doses, respectively. Most (88%) children (1-17 years) were unvaccinated, 138 received 1 measles vaccine dose and 24 received 2 doses. Of children aged 1-5 years 106 (13.5%) received 1 vaccine dose and were compared to unvaccinated children. Vaccinated children showed lower rates of clinical symptoms and lower risk for hospitalization compared to unvaccinated children (Odds ratio: OR = 4.8, 95%CI 1.12-20.2). Vaccine effectiveness of 79% was estimated for one measles vaccine dose against hospitalization.

CONCLUSIONS

Data on vaccine effectiveness reflect how well vaccines protect children against infection and morbidity. We evaluated the real-world effectiveness of measles vaccine, in an outbreak setting, and showed reduced morbidity in once-vaccinated children.

Characteristics and Genomic Diversity of Measles Virus From Measles Cases With Known Vaccination Status in Shanghai, China

Although the highly effective measles vaccine has dramatically reduced the incidence of measles, measles, and outbreaks continue to occur in individuals who received the measles vaccine because of immunization failure. In this study, patients who have definite records of immunization were enrolled based on measles surveillance in Shanghai, China, from 2009 to 2017, and genomic characteristics regarding viruses retrieved from these cases provided insights into immunization failure. A total of 147 complete genomes of measles virus (MV) were obtained from the laboratory-confirmed cases through Illumina MiSeq. Epidemiological, and genetic characteristics of the MV were focused on information about age, gender, immunization record, variation, and evolution of the whole genome. Furthermore, systematic genomics using phylogeny and selection pressure approaches were analyzed. Our analysis based on the whole genome of 147 isolates revealed 4 clusters: 2 for the genotype H1 (clusters named H1-A, including 73 isolates; H1-B, including 72 isolates) and the other 2 for D8 and B3, respectively. Estimated nucleotide substitution rates of genotype H1 MV derived using genome and individual genes are lower than other genotypes. Our study contributes to global measles epidemiology and proves that whole-genome sequencing was a useful tool for more refined genomic characterization. The conclusion indicates that vaccination may have an effect on virus evolution. However, no major impact was found on the antigenicity in Shanghai isolates.