What is “immunoamnesia,” a side effect of measles?

Although Spain, thanks to its vaccine shield, has avoided a global measles outbreak (we are the exception in Europe), the United States is experiencing an increase in measles cases (including 23 confirmed cases between December 1, 2023 and January 23, 2023). 2024 and seven more in Florida).

Measles, known for its characteristic red rash, is caused by the morbillivirus virus and is spread through the air. For every 10 unvaccinated people exposed to the virus, nine will get sick, making it one of the most contagious viruses. Although most cases of measles are mild, the infection can cause a number of potentially serious complications, including conditions that appear months or years after the initial infection.

Before the introduction of the measles vaccine in 1963, there were three to four million cases of the disease each year in the United States, resulting in approximately 48,000 hospitalizations, 400 to 500 deaths, and 1,000 cases of measles encephalitis. Since the vaccine was introduced, these rates have dropped by more than 99%.

“In some ways, we are victims of our own success, because when it is out of sight and out of mind, it is not considered a problem,” says Louis Ostrosky, an infectious disease physician and epidemiologist at UTHealth in Houston, US.

One of the main problems is that, given the contagiousness of measles, a very high percentage of people need to be vaccinated to prevent outbreaks. As Camilla Sabella, an infectious disease physician at the Cleveland Clinic in the US, explains, unless a community has a very high level of vaccination, as in Spain, “outbreaks will occur,” she says. “He really has a way of finding receptive people.”

Susceptible people include children too young to receive the first dose of the vaccine, people with weakened immune systems who cannot be vaccinated, and children who have received only one dose (two doses are needed for maximum effectiveness).

According to the UN, the World Health Organization (WHO) “declared measles elimination in Spain in 2017, and every year since then the WHO has ratified the country’s elimination status. In 2022, a single case of measles was confirmed in Spain. an unvaccinated adult returning from a trip from India.

Although most people who get measles recover fully, the disease is “associated with significant morbidity and mortality,” Sabella says.

A small number of people infected with the measles virus may later develop a disease called subacute sclerosing panencephalitis (SSPE), which occurs when the virus attacks the brain, where it remains dormant until it develops into SSPE years later. PEES is characterized by cognitive impairment, changes in behavior, problems with motor functioning (such as uncontrolled movements and seizures), and blindness.

In later stages of the disease, patients may lose the ability to walk or even fall into a coma. There is no cure for PEES. “It’s 100% fatal,” says Rik de Swart, a virologist at Erasmus University in Rotterdam, the Netherlands. “It’s a truly terrible disease.” For every 100,000 cases of measles, there are four to 11 cases of PEES, and this number increases to 18 for children who contract measles before their first birthday.

Scientists found that the vaccine saved lives because, in addition to protecting against measles, children no longer died from other common childhood infections such as diarrhea or respiratory illnesses.

“It has been known for decades that those who recover from measles are immunocompromised,” says Mansour Kharifar, a professor of immunology at Western University in London, Ontario, Canada, and are much more vulnerable to death from other, non-measles-related infections. .

These memory cells are responsible for recognizing and destroying pathogens it has encountered in the past. Once the virus destroys them, they are replaced by cells that preferentially recognize the measles virus. This allows the body to fight another measles infection, but impairs its ability to recognize other common pathogens, such as a cold or flu virus.

However, as de Swart notes, the good news is that this effect is not permanent. “It’s not that you lose everything,” says de Swart; “If you give yourself time and don’t expose yourself to the wrong pathogen at the wrong time, your system will return to its normal state.”

This immune amnesia is most pronounced in the first months after measles infection, but can persist for years.

Given that measles can suppress the immune response, experts worry that rising cases will worsen future pandemics.

In a 2021 study, researchers modeled the impact of lower measles vaccination rates on pandemics and found that a relatively small decline in vaccination rates could make it more difficult to contain a new pandemic due to immune amnesia.

“You may believe you have herd immunity, but because of the small effect of not getting vaccinated against measles, you don’t,” says Miguel Muñoz, a professor at the University of Granada and one of the authors of the 2021 paper. ; “The results can be dramatic.”

The measles vaccine, given in two doses (the first at 12 to 15 months of age and the second at four to six years of age), provides long-lasting protection against the infection.

One dose of the vaccine is approximately 93% effective in preventing infection; Two doses provide 97% protection that lasts for life.

“This is one of the most effective vaccines we have,” Ostrosky says; “Only very rarely do we need to revaccinate someone.”