Measles Strain Has Not Mutated Against Vaccines: icddr,b

2 August, Sunday: Amid concerns regarding the ongoing measles outbreak in the country, preliminary findings from an investigation by icddr,b have revealed no evidence of genetic mutations in the circulating measles virus that would allow it to evade the protection offered by currently administered vaccines.

According to data from the Directorate General of Health Services (DGHS), a total of 122,763 suspected and 15,272 laboratory-confirmed measles cases were recorded between March 15 and July 25, 2026. During the same period, 721 suspected deaths and 95 confirmed measles-related deaths were documented.

In response to the surge, researchers from icddr,b and the Bangladesh Shishu Hospital and Institute conducted an investigation involving 341 hospitalized children under the age of 14 between April 20 and May 21, 2026. Laboratory testing confirmed measles in 324 children, with the highest concentration among infants aged three to eight months (137 confirmed out of 141).

The study categorized the 341 suspected cases based on age and vaccination status:

• Under 9 months (ineligible for vaccine): 142 out of 146 tested positive (97.3%).

• Eligible but zero doses received: 122 out of 126 tested positive (97%).

• Received 1 dose: 44 out of 48 tested positive (92%).

• Received recommended 2 doses: 16 out of 21 tested positive (76%).

Researchers clarified that a reduction in positivity rates from ~97% in unvaccinated children to 76% among two-dose recipients aligns with expected vaccine protection. However, as this was a hospital-based cohort, it does not represent population-wide vaccine efficacy.

Genetic analysis confirmed that the circulating strain belongs to the B3 genotype (subclade B3), which matches strains identified in global measles outbreaks. Phylogenetic analysis of 55 full genome sequences (18 by icddr,b and 37 by IEDCR) identified four mutations in the epitope region of the virus's H protein. Nevertheless, as the measles virus remains a single serotype, existing vaccines retain their protective capacity.

Dr. Noor Jahan Maliha, Associate Scientist at the Virology Laboratory, Infectious Diseases Division at icddr,b, stated, "Given the magnitude of this outbreak, public concern regarding vaccine effectiveness is natural. Our investigation found no evidence that the virus is evading vaccine protection. Positivity rates were lower among children who received two doses. However, this hospital-based study cannot determine vaccine efficacy at the population level." She added that factors such as waning immunity, malnutrition, or individual health variations warrant further research regarding infected two-dose recipients.

Dr. Mustafizur Rahman, Senior Director of the Infectious Diseases Division at icddr,b, noted, "Vaccination remains the most effective tool to prevent measles and reduce severe illness. However, given that national vaccination coverage is reported to be relatively high, we must understand why this outbreak grew so large."

Dr. Kamrun Nahar, Assistant Scientist at the Virology Laboratory, remarked, "We need to determine why children are missing vaccinations and whether hidden immunity gaps exist in specific regions despite high national coverage figures. These findings will assist Bangladesh in refining vaccination strategies."

Dr. Tahmeed Ahmed, Executive Director of icddr,b, stated, "While these preliminary results answer critical questions, they highlight how much more we need to learn. icddr,b is initiating expanded research to investigate why some vaccinated children contracted the disease, factors behind severe illness, and the impact of malnutrition on immunity."

icddr,b has initiated clinical cohort studies across four divisional hospitals, alongside ongoing genomic surveillance, community studies, and a pilot study on zinc supplementation. Experts strongly urge parents not to delay or skip routine measles-rubella (MR) vaccinations.
//DBTech/ICDDR'b/SME//