The mysteries of measles

More than 30 years after the last major epidemic in Quebec, measles is once again making headlines. Researchers are trying to understand how the virus succeeds in destroying immunity to other diseases.

Amnesia

In the late 1980s, Brian Ward, an infectious disease specialist at McGill University, found himself at the forefront of a major discovery on measles, at Johns Hopkins University in Baltimore, by Diane Griffin.

In rich countries, the risk of measles is mainly linked to this immune amnesia. “We call this the measles paradox. The virus suppresses immunity to other infectious agents, but elicits a strong immune response. This is one of the reasons why the measles vaccine is so effective,” explains Rik de Swart, a virologist at the Erasmus Medical Center in Rotterdam, who is the other important researcher in this phenomenon.

Some researchers are working on drugs that could prevent measles from causing immune amnesia. “We are at the stage where we have identified several targets for action,” explains Richard Plemper, a microbiologist at Georgia State University whose work on the subject has just been published in Nature Communications. But we still have a long way to go. »

The success of the vaccine explains the slow progress. “There isn’t a lot of money for research because measles is generally not a problem in rich countries,” says Dr.^r Ward. It remains to be seen whether there will be more funds with the recent increase in the number of cases. »

Vitamin A

The other avenue of research into measles is treatment. “In the 1990s, a Johns Hopkins ophthalmologist wanted to reduce measles-related blindness in Indonesia by giving vitamin A to children,” says Dr.^r Ward. It worked, and mortality also fell by 30%. The success of vitamin A treatment has been replicated in South Africa. This is why the World Health Organization recommends vitamin A supplement programs.”

The D^r Ward is working on drugs that work similarly to vitamin A on the measles virus, but would be even more effective. The first results – on an animal model and serological – could be published this year.

The vaccine remains champion

All researchers interviewed by The Press believe that the best way to fight measles is with the vaccine.

But as it seems increasingly difficult to convince certain sectors of society to be vaccinated, research into treatments must continue, adds Mr. Plemper.

The D^D Griffin, a pioneer in immune amnesia, is now working on treatments. Last year, in the magazine Scientific Reports, it showed that the antiviral remdesivir, used against COVID-19, has a temporary effect on measles. “But as soon as we stop remdesivir, the measles starts again,” says the D^D Griffin. It still shows that a treatment is possible, we just need to try other molecules. »

Secondary failures

The outbreaks that have struck countries where measles had been eradicated over the past ten years have also led to a better understanding of vaccine failures. “The vaccine doesn’t work for about 5% of people,” says Dr.^r Ward. This is called primary vaccine failure. But there are also other people in whom immunity to measles wanes more quickly after vaccination. These secondary failures increase the proportion of vaccinated people who are vulnerable to measles by approximately 5% per decade. »

Secondary failures, however, are not linked to disease transmission. “An analysis of an outbreak in New York in 2018-2019 showed that people who have secondary measles vaccine failure are more likely to get sick, but less severely, and they rarely transmit the virus.” , said the D^r by Swart.

Could we consider a third dose of vaccine to counter secondary failures? “No, because these are people in whom the protection of the vaccine lasts less than a year,” says the D^r by Swart.

However, a debate is taking place on the response to these secondary failures: should these patients have their early childhood vaccines again, the protective effect of which is suppressed by the immune amnesia caused by measles? “Given the scale of the outbreaks this year, a lot of doctors are considering it,” says the D^D Griffin.