Almost half of the 60 children who died from confirmed measles were below nine months of age, government data showed, meaning they were not yet eligible for routine vaccination.

The government administers the first dose of the measles-rubella vaccine to children at nine months and the second at 15 months.

A total of 29 children died before reaching nine months of age, with 15 of them being six months or younger. The remaining children died at nine months of age or older, according to data collected by the Directorate General of Health Services (DGHS) of 60 confirmed measles deaths from 21 districts.

The youngest child was three months old, and the oldest was nine years old.

Earlier, before the launch of an emergency vaccination drive last month, the National Immunisation Technical Advisory Group had recommended lowering the age for receiving the measles vaccine to six months, as one-third of the children recently infected with measles are under nine months.

Children aged between six months and under five years are now being vaccinated under the special immunisation drive to control the outbreak. However, the timing for the routine vaccination remained the same.

Asked about the possible reasons behind the high number of deaths among children under nine months, Fazle Rabbi Chowdhury, associate professor of internal medicine at Bangladesh Medical University, gave a detailed explanation.

Babies who are breastfed are generally expected to remain protected against measles for at least nine months because of maternal antibodies, he said.

“That is why the first dose of the measles vaccine is administered at nine months of age.”

However, it does not mean that all children remain protected until nine months, as research suggests that antibody levels and protection may start declining in some children as early as six months.

Maternal immunity gradually wanes between six and nine months of age, and one study found that protection may decline in around 26 percent of cases. Children can become infected with measles once this protection decreases.

Measles infection itself usually provides stronger natural immunity afterwards, but some children may still die because of underlying comorbidities or other risk factors. These may include pneumonia, diarrhoea, meningitis, and other associated complications, he said.

Although it is not possible to say whether these children had weaker immune systems without detailed research, malnutrition could also be a major factor, something many paediatricians have pointed out, he said.

In addition, their mothers may not have been vaccinated or previously infected with measles.

If mothers lack immunity, children are less likely to receive protective antibodies. These factors may partly explain infections and deaths among children aged between six and nine months.

He, however, said the deaths of children below six months should be brought under rigorous research.

“It is important to investigate whether the measles virus circulating this time has undergone any mutation or structural change compared to previous strains. These are matters that need in-depth scientific research,” he added.

Nowadays, many mothers develop vaccine-induced immunity instead of natural immunity, which tends to last longer; however, this may not provide sufficient protection to their children until nine months of age, said Ariful Bashar, former superintendent of the Infectious Diseases Hospital in Dhaka.

“That’s why many of these children might not have received the necessary protection and died,” he said, adding that the issue should be investigated.

Besides, delayed admission to hospitals might be among other reasons behind the deaths, said Bashar, also a senior consultant at the hospital.

Asked about the deaths of many children within two days of admission, Fazle Rabbi said it was consistent with global trends.

If complications of measles -- like pneumonia, eye infections, measles-associated diarrhoea and encephalitis -- are not managed with hospital support within 48 hours, the risk of death increases significantly.

Almost all the children had fever and respiratory complications, which are typical symptoms of the highly contagious disease.

At least 11 children had pneumonia, while others showed additional complications such as diarrhoea and meningitis.

Meanwhile, six more suspected measles deaths were reported in the 24 hours until 8:00am yesterday, taking the total number of confirmed and suspected deaths to 415.

Of them, 65 were confirmed measles deaths and 350 were suspected deaths, according to the DGHS.

Experts said the country has to vaccinate at least 95 percent of children, which is known as “herd immunity”, through the ongoing special campaign and routine vaccination to stop measles from spreading and protect all children. If herd immunity is achieved, the virus cannot spread easily, which helps protect both vaccinated and unvaccinated people.