Beyond the vaccine: Why is measles still spreading?

Bangladesh is still struggling to bring the ongoing measles outbreak under satisfactory control.

Since the outbreak began on March 15, nearly 140,000 infections and around 890 child deaths have been reported.

At the same time, measles outbreaks have increased in several countries in recent years. Measles vaccination remains highly effective.

One dose provides about 93% protection, while two doses provide around 97% protection.

Therefore, although a small number of vaccinated people may still become infected, vaccination substantially reduces the risk of infection and severe disease.

Measles is one of the most contagious infectious diseases. To stop sustained transmission, at least 95 per cent of a population needs to have adequate immunity.

A vaccination rate of 90 per cent may appear high, but it is not enough to prevent measles from spreading.

The situation becomes more dangerous when unvaccinated children are concentrated in the same neighbourhood, slum, refugee camp or densely populated area. In such communities, the virus can spread very quickly.

Another important issue is that one dose of vaccine is not the same as two doses.

One dose provides about 93 per cent protection, while two doses provide around 97 per cent protection.

Although the first dose is highly effective, some children do not develop sufficient immunity after it.

The second dose provides additional protection to these children.

Therefore, it is important not only to ensure that children receive the vaccine but also to make sure that they complete the recommended vaccination schedule.

There is also a lesson from the disruption of routine immunisation. When children miss their vaccines at the recommended time, they remain vulnerable for years.

Even a temporary gap in vaccination can gradually create a larger group of susceptible children.

According to the WHO 2026 assessment cited in the article, vaccination gaps during 2024-2025, together with the absence of regular national campaigns since 2020, contributed to an increase in the number of vulnerable children and played a role in the current situation.

Measles spreads very easily through coughing, sneezing and respiratory droplets. The virus can also remain infectious for some time in enclosed spaces after an infected person has left.

This makes crowded households, schools, hospitals, slums and refugee camps particularly vulnerable.

When a large number of people in a community are not adequately protected, one infected person can quickly spread the virus to many susceptible children.

Maintaining vaccination coverage above 95 per cent is therefore essential.

It is also important to understand that no vaccine provides 100 per cent protection.

Even after two doses, a small number of vaccinated people may still develop measles, especially during a major outbreak when exposure to the virus is intense.

However, such cases are relatively uncommon, and vaccination greatly reduces the risk of infection and, more importantly, severe disease.

Therefore, the occurrence of measles in a vaccinated child should not be considered proof that the vaccine does not work.

A child’s nutritional condition also plays an important role. Malnourished children may have weaker immune responses and may not develop adequate protective antibodies after vaccination.

They are also more vulnerable to complications if they become infected.

Vitamin A deficiency can further increase the severity of measles. For this reason, controlling measles must go together with improving child nutrition.

Measles can also become more serious when other infections occur at the same time.

Some studies have reported co-infections, including adenovirus, among measles patients.

Such infections may contribute to greater disease severity and complications.

This means that doctors and health workers need to look beyond measles alone when caring for affected children.

There is another important but less visible consequence of measles known as “immune amnesia”. After measles infection, the body’s immune memory may become weakened.

The virus can damage certain memory cells that help the immune system recognise and respond to infections encountered previously.

As a result, a child who has recovered from measles may remain more vulnerable to other infections for some time.

Bangladesh’s current experience with measles gives us an important message. The effectiveness of the vaccine is only one part of measles control.

We also need high and sustained vaccination coverage, timely vaccination, completion of both doses and special attention to children who have been missed by routine immunisation.

Every child who has not received the vaccine should be identified and brought into the vaccination programme.

Children who have received only one dose should be encouraged to complete the schedule.

Areas with low vaccination coverage need special attention, particularly densely populated and disadvantaged communities.

At the same time, improving child nutrition and strengthening disease surveillance and outbreak response should remain priorities.

Vaccination protects an individual child, but high vaccination coverage protects the whole community.

When some children remain outside the vaccination programme and these gaps continue for several years, the virus gets new opportunities to spread.

The answer to the current measles outbreak, therefore, is not to lose confidence in vaccination but to strengthen it.

Bangladesh must ensure that every eligible child receives the recommended doses and that population-level immunity remains above 95 per cent.

Only sustained and equitable immunisation, combined with better nutrition and effective public-health measures, can help prevent future large-scale measles outbreaks.

(The writer is a Public Health Specialist and Director, Medical Services, BRB Hospital).