Published: 12:02 AM, 03 August 2026
No proof of genetic changes in measles viruses: icddr,b
Preliminary findings from an icddr,b investigation have found no genetic evidence that the measles virus circulating in Bangladesh has escaped the protection provided by the existing vaccine.
The Preliminary findings also show infants too young for routine vaccination (less than 9 months) are the largest affected group, said a iccdr,b press release on Sunday.
The scale of the outbreak has led some people to question whether the measles virus has genetically changed enough to reduce vaccine effectiveness, but the findings do not support the belief that the vaccine has become ineffective, reports UNB.
Children who had received both recommended doses were less likely to test positive among the suspected cases investigated.
Genetic analysis also found that the circulating virus belongs to the B3 genotype, which has been reported in outbreaks elsewhere in the world.
According to the Directorate General of Health Services (DGHS), 122,763 suspected cases and 15,272 laboratory-confirmed cases were reported between 15 March and 25 July 2026.
During the same period, 721 suspected and 95 confirmed measles-related deaths were recorded.
Researchers from icddr,b and Bangladesh Shishu Hospital and Institute (BSH&I) investigated 341 children aged up to 14 years who were admitted to Bangladesh Shishu Hospital & Institute (BSH&I) with suspected measles between 20 April and 21 May 2026. Laboratory testing confirmed measles in 324 children.
Children aged between three and eight months constituted the largest affected group, with 137 confirmed cases.
The researchers divided the 341 children into four groups according to their age and vaccination status. Among 146 infants who were below nine months and therefore too young for routine vaccination, 142 tested positive, representing 97 percent.
Among 126 children who were old enough to be vaccinated but had received no dose, 122 tested positive, or 97 percent. Of the 48 children who had received one dose, 44 tested positive, or 92 percent.
Among 21 children who had received both recommended doses, 16 tested positive, or 76 percent. This does not mean that 76 percent of all fully vaccinated children are contracting measles. All the children in the investigation had already been admitted to hospital with suspected measles.
The percentage refers only to the 21 fully vaccinated suspected patients included in this hospital investigation.
The progressively lower positivity, from approximately 97 percent among children with no vaccine protection to 76 percent among those who had received both doses, is consistent with vaccination providing protection.
However, a wider study with unaffected children for comparison is needed to measure how effectively the vaccine is working during the outbreak.
"The size of this outbreak has understandably raised concerns about whether the vaccine is still working. Our findings provide no evidence that the virus has escaped vaccine protection. We observed lower positivity among children who had received both doses, although this hospital-based investigation cannot provide a population-level estimate of vaccine effectiveness," said Dr Noorjahan Maliha, Associate Scientist in the Virology Laboratory of the Infectious Diseases Division at icddr,b.
The finding that 16 fully vaccinated children were confirmed with measles requires further investigation.
Possible explanations include some children not developing a sufficiently strong immune response after vaccination, antibody protection declining over time, malnutrition or other health and individual factors. The present investigation was not designed to determine which of these factors contributed to infection.
icddr,b conducted phylogenetic analysis, which compares the genetic sequences of viruses to understand how closely related they are and how they may have spread.
The analysis covered 55 whole-genome sequences, including 18 samples sequenced by icddr,b and 37 by the Institute of Epidemiology, Disease Control and Research (IEDCR).
Phylogenetic analysis showed that all viruses belonged to the B3 subclade and were similar to B3 viruses reported in other countries.
Researchers also identified four changes, or mutations, in regions of the virus's H protein epitopes that are recognised by antibodies.
The H protein helps the virus enter human cells and is one of the principal targets of vaccine-induced antibodies. Some of these mutations have previously been reported in measles viruses circulating elsewhere.
Their presence does not mean that the virus has become resistant to the vaccine.
The findings also highlight a period of vulnerability among young infants. In Bangladesh, the first routine measles-rubella vaccine is provided at nine months and the second at 15 months.
"Vaccination remains the most effective way to prevent measles and reduce the risk of severe illness. At the same time, we need to understand why this outbreak became so large despite comparatively high reported national vaccination coverage," said Dr Mustafizur Rahman, Senior Director of the Infectious Diseases Division at icddr,b.
"We need to determine why children miss vaccination and whether reported national coverage conceals communities with substantial immunity gaps. Evidence from these studies will help Bangladesh refine its vaccination strategy and better protect children during future outbreaks," Dr Kamrun Nahar, Assistant Scientist of the Virology Laboratory, added.
"These preliminary findings answer some important questions, but they also show how much more we need to understand. icddr,b is developing a wider research response to examine why some vaccinated children became infected, what factors are contributing to severe disease and death, how malnutrition may affect protection and when infants lose antibodies received from their mothers," said Dr Tahmeed Ahmed, Executive Director of icddr,b.
