Vaccination against measles and polio protects children from dying from other diseases

Children vaccinated against measles and polio are protected from much more than just these two diseases.

A new study suggests that removing oral polio vaccination from national vaccination programmes would probably be a bad idea, even when or if polio is finally eradicated.

The study only investigated the live oral polio vaccine, not the inactivated polio vaccine.

The research also shows how polio vaccination campaigns in Guinea-Bissau reduced the benefits of measles vaccination.

The research has been published in the International Journal of Infectious Diseases.

“Our results show that the campaigns to vaccinate more children in Guinea-Bissau against polio not only affect the risk of contracting polio but also affect the risk of dying from many other infectious diseases. Further, children not vaccinated against polio in a campaign are better protected from dying from other infectious diseases if they were instead vaccinated once more against measles,” explains a researcher involved in the study, Sebastian Nielsen, University of Southern Denmark, Odense.

The research emanated from the Bandim Health Project field station in Guinea-Bissau.

Vaccination offers more protection than expected

Sebastian Nielsen is part of a research group that has focused on the non-specific effects of vaccination for many years.

This research indicates that vaccination with live vaccines, especially oral polio vaccine and measles vaccine, protects against much more than just these diseases.

The reason is probably that the live vaccines train the immune system to equip it better to tackle a variety of viruses and bacteria and not just poliovirus or measles virus.

“We know that both types of vaccination can reduce child mortality from all causes in Africa and Asia, and in this study we aimed to investigate how these vaccinations affect the mortality risk among children – depending on when they receive them,” says Sebastian Nielsen.

Compared data from three randomised controlled trials

The researchers compared the mortality risk among children in Guinea-Bissau who had been given a second measles vaccine early in life in three randomised controlled trials.

The studies investigated the effect of measles vaccination between 2003 and 2009; from 2011 to 2019 in an urban area; and from 2015 to 2019 in a rural area.

The difference between the trials was that the 2003–2009 period did not have many polio vaccination campaigns but the later trials did.

This probably resulted in far fewer children receiving polio vaccination before being vaccinated against measles in the early 2003 to 2009 trial.

Further, the trials did not just study the effect of vaccination against measles but studied the effect of giving children an extra measles vaccination at an earlier age than in the standard childhood vaccination programme.

Children in Guinea-Bissau are routinely vaccinated against measles from nine months of age, but in the trials they received an extra measles vaccination from the age of four to five months.

“The first trial found that the additional measles vaccination reduced child mortality by 30% but the other two trials could not replicate this finding. This study attempted to understand and explain the differences between the studies,” explains Sebastian Nielsen.

Increased efforts to eradicate polio

The researchers investigated whether polio vaccination could account for the difference between the trials.

There had been very few campaigns to vaccinate children against polio in 2003–2009 and many more in the later periods.

During the campaigns in Guinea-Bissau, vaccination workers go from house to house and offer parents of children younger than five years the opportunity to have their child vaccinated against polio. At other times, parents could go to centres that had been established.

This meant that virtually all infants had been vaccinated through the campaigns.

Polio vaccination overrides the protective effect of measles vaccination

The results indicate that the oral polio vaccination campaigns leading to more polio-vaccinated children may be the reason why the additional measles vaccination did not seem to have the same protective effect as previously.

However, this does not mean that the children are not protected. The polio vaccination just seems to already protect the children so much that an additional measles vaccination has no effect.

The trials showed that vaccinating children against measles without polio vaccination was associated with 36% reduced mortality.

This survival advantage disappeared for those vaccinated against polio.

“We theorise that the children who do not receive an additional measles vaccination at four to five months old especially benefit from being vaccinated against polio during the campaigns and that this can explain the difference between the trials,” says Sebastian Nielsen.

Oral polio vaccination should continue

According to Sebastian Nielsen, the study suggests why vaccination in low-income countries is especially important, since these countries have high child mortality, especially from infectious diseases.

Children vaccinated with live vaccines, however, appear to develop immunity to many potentially fatal infectious diseases other than measles and polio.

This is why Sebastian Nielsen is concerned that health authorities globally are considering removing polio vaccination from childhood vaccination programmes when and if polio is eventually eradicated.

“In my research, I have found that oral polio vaccination campaigns reduce mortality by 25–30% in addition to protecting against polio. Continuing oral polio vaccination therefore probably makes sense. In any case, we should investigate the full effects of oral polio vaccination and whether we should continue to vaccinate children in low-income countries even if they no longer risk developing polio,” he concludes.