As measles cases surge worldwide, experts are raising alarms about a lesser-known danger: immune amnesia.
The highly contagious virus doesn’t just cause a rash and fever — it can also wipe out the immune system’s memory, leaving survivors vulnerable to infections they’ve fought off before, like the flu, a cold, or even diseases they’ve been vaccinated against.
Health Canada warns that measles can lead to serious immune suppression, known as immune amnesia. This can increase the risk of other illnesses and even raise the chances of death for months or even years after the infection, the health agency states on its website.
“Immune amnesia basically destroys your immune system. And with respect to the measles virus, it can infect the cells that process the memories or prior immune or viral infection and other pathogens, it can infect those cells and kill the cells, so it erases the actual physical memory,” explained Stephen J. Elledge, a professor of genetics and medicine at Harvard Medical School.
“And it depletes that to the point where you no longer can respond to proper pathogens as well as you would have been able to, had you not had measles.”
Elledge, who has published research on immune amnesia, said the side effect is especially concerning as measles outbreaks continue in Canada and the United States, potentially leaving many people vulnerable to other infections after contracting the virus.
A 2019 study published in Science, co-authored by Elledge, found that measles can erase up to 73 per cent of a person’s protective immune memory.
Because your immune system is left in a near-blank state, similar to that of a baby’s, studies show it can take years to slowly rebuild and relearn how to defend against infections.
Measles, known for its characteristic red rash, is one of the most contagious viruses on the planet, with an R number of 12 to 18 — meaning one infected person can spread it to up to 18 others in an unvaccinated population. To put that in perspective, COVID-19’s original strain had an R number of about two to three, and even highly transmissible variants like Omicron rarely exceeded 10.
Once declared eradicated in Canada in 1998, measles is now making a comeback, spreading rapidly in recent months, especially in places like Ontario, due to declining vaccination rates.
The virus can cause serious complications, including severe illness and even death. And another side effect is immune amnesia.