Can you still get measles if you have been vaccinated?

The number of measles cases in the United States continues to increase, with more than 550 cases reported from January to April, according to the Center for Disease Control and Prevention (CDC). This is the second highest number of measles cases reported in any year since 2000, says the CDC.

According to the CDC, many of this year's cases are due to ongoing measles outbreaks in several US cities and most infected people have not been vaccinated. But if you have been vaccinated, can you still contract the disease?

Although it is possible to get measles even if you have been vaccinated, it is quite rare: two doses of measles, mumps and rubella vaccine (MMR) – which are administered as part of of the US standard vaccination program for children – are 97% effective in preventing measles, according to the CDC. This means that about 3% of people who receive two doses of measles vaccine will get measles if they are exposed to the virus. [27 Devastating Infectious Diseases]

The reason why some fully vaccinated people catch measles is unclear, but their immune system may have failed to respond to the vaccine, says the CDC. (However, if a person is fully vaccinated and contracting measles, they are more likely to have a mild case of the disease.)

In addition, some people are at slightly higher risk of contracting measles because they received only one dose of MMR vaccine. Although the measles vaccine was developed in 1963, it was not until 1989 that health authorities recommended that a child be given two doses, according to the CDC.

This means that there are "many adult people now who have only received a" dose of MMR, said Dr. Amesh Adalja, a senior researcher at the Johns Hopkins Health Security Center at Baltimore. A dose of MMR is still more than 90% effective in preventing measles, but it is not as good as two doses, said Adalja.

Adults who have received a single dose of MMR as a child may consider taking a second dose, Adalja told Live Science. In situations where there are epidemics, "I do not think it's a bad idea," he said.

In addition, some people who received the measles vaccine in the 1960s may need to be revaccinated. In fact, between 1963 and 1967, some people received a form of measles vaccine known as the "inactivated" (killed) vaccine, which was not effective, according to the CDC. People who have received this form of vaccine or who were vaccinated before 1968 and do not know what type of vaccine they received should be revaccinated with the current form of "live attenuated" vaccine, the CDC says.

Loss of immunity?

Another question that people may have is whether vaccine protection decreases over time. Generally, people who have received two doses of MMR are considered to be protected for life, which means they do not need a booster shot, according to the CDC.

Still, some things may decrease with age, Adalja said.

There is a way to check your level of protection against measles. You can get a blood test that measures the levels of antibodies against the measles virus. However, doctors do not routinely use this test on patients – it is more often used by health care workers who are generally at higher risk of being exposed to measles. But it can be used in other situations: for example, for students who need to prove that they are immunized against measles, according to the University of Rochester Medical Center.

In general, the CDC recommends that people who do not have written documentation about MMR vaccination be vaccinated. However, people born before 1957 are considered susceptible to being immunized against the virus (since most people born at that time were naturally infected with the virus) and therefore do not need to be infected with the virus. be vaccinated.

Originally published on Science live.