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A preliminary investigation in Bangladesh offers reassurance regarding the effectiveness of measles vaccines amidst a significant outbreak. Findings from the icddr,b (International Centre for Diarrhoeal Disease Research, Bangladesh) indicate that children who received both recommended doses of the measles vaccine were less likely to test positive for the virus among hospitalized suspected cases.

The study, which examined 341 children aged up to 14 years admitted to the hospital with suspected measles between April 20 and May 21, found that only 76% of those fully vaccinated tested positive. This contrasts with higher positivity rates among unvaccinated or partially vaccinated children, with rates reaching approximately 97% for those too young to be vaccinated and those who had received no doses.

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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.

Concerns had arisen that the measles virus might have undergone genetic changes, potentially diminishing vaccine efficacy. However, genetic analysis conducted by the researchers revealed that the circulating virus belongs to the B3 genotype, a strain reported in outbreaks globally. This analysis found no proof of genetic mutations that would render the vaccine ineffective.

"Our findings provide no evidence that the virus has escaped vaccine protection," stated Noorjahan Maliha, an associate scientist at icddr,b. She emphasized that while the hospital-based investigation shows a trend of lower positivity among fully vaccinated children, it cannot provide a definitive population-level estimate of vaccine effectiveness. A broader study, including children not suspected of having measles, is necessary to accurately measure the vaccine's performance during this outbreak.

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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.