As a viral infection that starts in the respiratory system, measles, like the virus that causes Covid-19, is an acute, highly contagious disease. Unlike Covid-19, however, measles can already be prevented through vaccination.
And the measles vaccine, as far as vaccines go, is extremely good — both remarkably safe and effective. Two doses of vaccine in childhood protect about 97% of the children who receive it.
Still, scientists are always looking for new information that could help them create a vaccine that would provide even better — and longer-lasting — protection.
Toward that end, a new study helps shed new light on the nature of protection offered by the attenuated measles virus, which is used in the vaccine, compared with immunity induced by natural measles infections.
In the study, conducted in macaques, natural virus infection pointed to consistent protection for decades. Protection levels provided through the measles vaccine, by contrast, can decrease over time — though people who receive the measles, mumps, and rubella (MMR) vaccine according to the U.S. vaccination schedule are still usually considered protected for life against measles and rubella.
Researchers stressed that the findings don’t mean the current measles vaccine is ineffective. And as Velislava Petrova, a postdoctoral fellow in human genetics at the Wellcome Sanger Institute, pointed out, a natural measles infection can have serious consequences on the immune system, unlike any effects of the live-attenuated virus.
“If you contract the natural virus, you face immunosuppression after measles because it causes such a strong response in the immune system, which is really a negative effect. The vaccine, though, has a less strong effect on the immune cell compartment, but the body still manages to generate protection,” said Petrova.
Saad Omer, director of Yale University’s Institute for Global Health, also stressed the important of vaccine as a means of protection against infection.
“What doesn’t kill you makes you stronger. But then if you’re focusing on the stronger part, you don’t get it,” he said.
The new study, led by Wendy Lin, pathology resident at the Columbia University Medical Center and her colleagues, was recently published in the journal Science Translational Medicine.
In the study, the researchers compared characteristics of infection with wild-type virus and with live-attenuated virus in rhesus macaques. Eight male macaques were infected with wild-type virus, and aerosol delivery of live-attenuated virus, in the form of dry powder, was used to infect 17 male and 14 female macaques. The results demonstrated that in infected macaques, wild-type virus replicated more efficiently and thoroughly to B and T cells that are actively involved in initiating an immune response to viral infections.
On the other hand, live-attenuated virus, though replicated efficiently in the respiratory tract, had limited ability to spread in the B and T cells, leading to a less vigorous immune response.
“We observe a huge difference in the antibody response. Monkeys with wild-type virus have higher antibody titer [number of antibodies in the blood], which indicates that this protection could be very long-lasting,” Lin told STAT.
Measles spreads through air after an infected individual coughs or sneezes. The infectivity of the virus is so high that if one person has it, 9 out of 10 people with close contact with that person will also become infected if not protected, according to the Centers for Disease Control and Prevention.
“We need to remember is that measles is, in fact, one of the most infectious viruses that we know. … So you can imagine what the spread of said virus would be if the vaccine weren’t around,” said Petrova.
Petrova said the new study is an important finding that enhances scientists’ understanding of the immunological response of wild-type virus — but “they should not be misunderstood when it comes to efficacy and the importance of vaccination, which is key to managing measles outbreaks.”
While the research sheds light on the importance of developing stronger vaccines in the future, it also raises questions of whether different delivery methods, such as aerosol delivery as opposed to the traditional intramuscular delivery, might make the immunity more long-lasting.
“Our research can really help understand more about why there’s such a difference in the immunological response, and also improve our knowledge about the design of a future vaccine,” said Lin.