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An investigation by the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) has found no genetic evidence that the measles virus circulating in the country has evolved to evade existing vaccines, easing fears amid one of the worst outbreaks in recent years.
The preliminary findings, released on August 2, indicate that the current measles strain remains susceptible to vaccine protection. However, the study highlights that infants under nine months—too young to receive the first routine measles-rubella (MR) vaccine—are the most affected group.
The outbreak continues to intensify. According to the Directorate General of Health Services (DGHS), four more children died in the 24 hours leading up to 8am on Saturday, bringing the total death toll since March 15 to 844, including 96 laboratory-confirmed cases. During the same period, more than 1,000 new suspected cases and over 100 confirmed infections were reported, pushing cumulative figures to over 130,000 suspected and 16,000 confirmed cases.
To examine concerns about possible viral mutation, researchers from icddr,b and Bangladesh Shishu Hospital and Institute studied 341 children up to 14 years old who were hospitalised with suspected measles between April 20 and May 21. Of these, 324 cases were laboratory-confirmed.
Infants aged three to eight months represented the largest group of infections. Among 146 infants under nine months, 97% tested positive. Similarly, high positivity rates were found among unvaccinated children and those who had received only one dose of the vaccine.
Researchers cautioned that these figures reflect only hospitalised cases and do not indicate overall vaccine failure. Lower infection rates among fully vaccinated children still support the vaccine’s effectiveness.
Genetic analysis of 55 virus samples showed all belonged to the B3 genotype, a strain also seen in outbreaks globally. Although a few mutations were detected, researchers said these are not new and do not reduce vaccine effectiveness.
“The scale of this outbreak has raised understandable concerns, but our findings show no evidence that the virus has overcome vaccine protection,” said Dr Noorjahan Maliha, associate scientist at icddr,b.
The study also highlights a critical vulnerability period before infants receive their first vaccine dose at nine months. Analysis of mother-child samples showed that protective maternal antibodies decline rapidly, leaving infants aged three to eight months particularly exposed.
Experts stressed that vaccination remains the most effective way to prevent measles and severe complications. They also called for further investigation into why such a large outbreak has occurred despite reportedly high vaccination coverage, including whether gaps exist in certain communities.
Health specialists urge renewed focus on immunisation coverage and timely vaccination to contain the outbreak and protect the most vulnerable.