The variety of measles and rubella viral genotypes are on declining worldwide, according to a study published in the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report. Continued virologic surveillance among all reported cases will bolster the progress toward elimination of these diseases.

This report added to the results of a previous report, contributing further genetic data on measles and rubella viruses from 2016 to 2018. The 2018 dataset included monthly case-based surveillance reports from 184 countries that included 317,445 serum specimens, which was 101% greater than the number of specimens in 2016. Among these specimens, 87% (n=275,020) were tested for measles, and 64% of those (n=203,898) were also tested for rubella. Over approximately 3.5 years, the global Measles Nucleotide Surveillance database demonstrated a 93% increase in documented measles virus sequence, increasing from 24,571 in July 2015 to 47,521 sequences at the end of 2018. Similarly, the global Rubella Nucleotide Surveillance demonstrated a 73% increase in rubella virus sequences, from 1820 to 3149 over the same period. 

The measles virus was detected in 29% (n=78,950) of specimens, and rubella was detected in 6% (n=11,874). Of the 24 recognized measles virus genotypes, 6 were detected in the 2016 to 2018 period, and this decreased to 4 in 2018 (2016: B3, D4, D5, D8, D9, and H1; 2018: B3, D4, D8, and H1). There was also an 87% (2625 to 333) decrease in the number of reported genotype H1 measles cases, with B3 and D8 comprising 95% of all cases. The H1 genotype was the only genotype with a nondecreasing diversity index between 2016 and 2018. Among the 32 identified strains between 2016 and 2018, 2 were found in all 6 regions, accounting for 95% of reported sequences.

Five of the 13 recognized rubella genotypes were detected between 2016 and 2018, and then further decreased to 2 genotypes by 2018. However, rubella is still endemic everywhere but the Americas, and worldwide data on the virus was incomplete.

Limitations to this study included a lack of representation of transmission chain sequences in countries without advanced viral surveillance, as well as a lack of alignment between distributions of measles and rubella reported to global databases and the known distribution.

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Study authors concluded that “With increased sequence reporting and use of new sequencing approaches, [the Global Measles and Rubella Laboratory Network] will provide enhanced support for monitoring progress toward and verifying achievement of measles and rubella elimination.”

Reference

Brown KE, Rota PA, Goodson JL, et al. Genetic characterization of measles and rubella viruses detected through global measles and rubella elimination surveillance, 2016–2018. MMWR Morb Mortal Wkly Rep. 2019;68(26):587–591.