No genetic change in measles virus, under-9-month-olds most at risk

Children under nine months of age, who have not yet reached the routine vaccination age, are the most affected in the ongoing measles outbreak. A preliminary study by researchers from icddr,b and Bangladesh Children's Hospital and Institute has found that the detection rate of measles is highest among this age group. The study also found no evidence of genetic changes in the measles virus circulating in the country.

Researchers said the first dose of the measles-rubella (MR) vaccine is given at nine months of age in Bangladesh. Before that, children rely primarily on maternal antibodies and existing herd immunity in the community. However, even after vaccination, natural protection wanes within a few months, leaving children aged three to eight months most vulnerable.

Researchers from icddr,b and Bangladesh Children's Hospital and Institute conducted a study on 341 suspected measles patients under 14 years of age admitted to hospital between April 20 and May 21. Of them, 324 were confirmed positive for measles through laboratory testing. The study found that children aged three to eight months were the most affected. Among 141 children in this age group, 137 tested positive for measles.

Analysis divided children into four groups based on age and vaccination status. Among children under nine months who were not yet eligible for vaccination, 142 out of 146 tested positive for measles. Among children who were eligible but unvaccinated, 122 out of 126 tested positive. Among children who received one dose, 44 out of 48 tested positive. Among children who received two doses, 16 out of 21 tested positive for measles. According to researchers, the relatively lower infection rate among children who received two doses is consistent with the protection offered by the vaccine.

The study said children under nine months do not receive the vaccine and depend on maternal antibodies. However, a previous small-scale icddr,b study found that these antibody levels decline rapidly within the first few months of life. Protective antibodies were no longer detected in observed children aged three to eight months. Researchers cautioned, however, that the study was conducted on only 16 children, so larger-scale research is needed to confirm the findings.

icddr,b Executive Director Dr Tahmid Ahmed said detailed research is ongoing into why some children are still affected despite vaccination, the causes behind severe illness and death, how malnutrition affects immunity, and when children lose maternal antibodies.

Researchers analysed 55 complete measles virus genome sequences, of which 18 samples were sequenced by icddr,b and 37 by the Institute of Epidemiology, Disease Control and Research (IEDCR). The analysis found all samples belonged to the B3 genotype, which has also been identified in ongoing outbreaks in various countries worldwide. Four mutations were identified in the H protein epitope region of the virus. However, researchers said these are not new; similar changes have been observed in other countries previously.

icddr,b Associate Scientist Dr Noorjahan Maliha said it is natural for people to be concerned about vaccine effectiveness during a major outbreak. However, the investigation found no evidence that the virus is evading vaccine protection. She noted that the detection rate among children who received two doses was comparatively lower, but the fact that 16 vaccinated children still contracted the infection warrants further investigation.

icddr,b Senior Director of the Infectious Diseases Division Dr Mustafizur Rahman said vaccination is the most effective way to prevent measles. However, despite relatively high national vaccination coverage, he said it is important to investigate why such a large outbreak has occurred.