No genetic evidence of vaccine-resistant measles strain in Bangladesh: icddr,b
According to the Directorate General of Health Services (DGHS), four more children died from measles and measles-like symptoms in the 24 hours until 8am today.
An investigation by the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) has found no genetic evidence that the measles virus circulating in Bangladesh has evolved to reduce the protection offered by the existing vaccine, easing concerns amid the country's worst measles outbreak in years.
The preliminary findings, released today (2 August), also identified infants younger than nine months -- too young to receive the first routine measles-rubella (MR) vaccine dose -- as the hardest-hit age group.
The findings come as the outbreak continues to spread. According to the Directorate General of Health Services (DGHS), four more children died from measles and measles-like symptoms in the 24 hours until 8am today, raising the combined death toll since 15 March to 844, including 748 suspected and 96 laboratory-confirmed measles-related deaths.
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During the same reporting period, 1,022 new suspected and 115 laboratory-confirmed cases were recorded, taking the cumulative totals to 130,083 suspected and 16,295 confirmed infections. Since the outbreak began, 112,620 suspected patients have been hospitalised, of whom 108,283 have recovered.
Infants most affected
To investigate concerns that the virus had mutated, researchers from icddr,b and Bangladesh Shishu Hospital and Institute (BSH&I) studied 341 children aged up to 14 years admitted with suspected measles between 20 April and 21 May. Laboratory tests confirmed infection in 324 children.
Children aged three to eight months accounted for the largest affected group, with 137 confirmed cases.
Researchers grouped the children by age and vaccination status. Among 146 infants below nine months, 142 (97%) tested positive. Among 126 vaccine-eligible but unvaccinated children, 122 (97%) were positive. Of 48 children who had received one vaccine dose, 44 (92%) tested positive, while 16 of 21 (76%) who had received both recommended doses were confirmed with measles.
Researchers stressed this does not mean 76% of all fully vaccinated children contract measles, as the study involved only hospitalised children already admitted with suspected infection. The lower positivity among vaccinated children is consistent with vaccine protection, although a population-based study is needed to measure vaccine effectiveness 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," said Dr Noorjahan Maliha, associate scientist at icddr,b's Virology Laboratory.
She said the hospital-based investigation cannot provide a population-level estimate of vaccine effectiveness, while the 16 infections among fully vaccinated children require further investigation.
No evidence of vaccine escape
Researchers conducted phylogenetic analysis of 55 whole-genome sequences – 18 sequenced by icddr,b and 37 by the Institute of Epidemiology, Disease Control and Research (IEDCR).
All belonged to the B3 genotype, which has also caused outbreaks in several other countries. Although four mutations were identified in the virus's H protein, researchers said they have been reported previously and do not indicate resistance to vaccine-induced immunity.
Window of vulnerability
The findings also highlight a vulnerable window for infants. In Bangladesh, the first routine MR vaccine is given at nine months and the second at 15 months. Before receiving the first dose, infants rely partly on maternal antibodies and community protection created through widespread vaccination.
An analysis of stored samples from 16 mother-child pairs found maternal measles antibodies declined rapidly, with no protective antibodies detected among children aged three to eight months.
"Vaccination remains the most effective way to prevent measles and reduce the risk of severe illness," said Dr Mustafizur Rahman, senior director of icddr,b's Infectious Diseases Division. He called for investigations into why such a large outbreak occurred despite high reported vaccination coverage.
Dr Kamrun Nahar, assistant scientist at the Virology Laboratory, said authorities also need to determine why children miss vaccination and whether national coverage masks communities with significant immunity gaps.
