How measles impacts your immune system

For people who grew up prior to 1966, getting measles during childhood was so commonplace, it may have seemed like a mild disease: everywhere, children were getting sick, but once the rash was gone, most of them recovered.

But it’s not a mild disease. Measles and its complications can be fatal. It’s easy to see the outward signs of a measles infection: the rash, the coughing, the fever, the runny nose and eyes. What you don’t see is how the measles virus suppresses the immune system, leaving you more vulnerable to other serious illnesses and breaking down defences you’ve already built up.

Measles and your immune system

A measles infection starts when a susceptible person breathes in the measles virus, which makes its way into the lungs where it is taken up by cells belonging to the body’s immune defence system. From there, it hitches a ride on other immune cells and is spread through the bloodstream to infect cells in almost all organ systems.

The measles virus can be associated with serious side effects and complications, such as pneumonia or encephalitis. These may be caused by a combination of direct tissue damage from the attacking measles virus, inflammation caused by the immune system trying to fight off the infection, and suppression of the immune system providing an opportunity for bacterial infections.

The exact way that the measles virus infection supresses the immune system is not completely understood. Recent studies suggest that the immune system’s ‘memory’ cells may be affected, leading to a state of ‘immune amnesia’ where your body temporarily ‘forgets’ how to respond.

Your suppressed immune system leaves you vulnerable to other infections, whether they are germs your body has never encountered before, or something that you would normally already be immune to. This vulnerability may last from a few months up to three years. That’s a long time to be vulnerable, especially for young children.

Measles’ superpower: extreme contagiousness

As well as being able to cripple your immune system, the infectivity of the measles virus is legendary: up to 9 out of 10 susceptible people will develop measles if they come into contact with an infected person.

A measles-induced cough can easily and efficiently launch lots of viral particles into the air, where they can linger on surfaces for a long time (up to two hours, in some cases). This can be especially dangerous in aeroplane toilets, doctors’ waiting rooms or other places where many people share a small air space.

Vaccination trains your body to defend itself

Vaccination is the best way to protect yourself against one of the most infectious diseases known to humankind. Unlike a naturally-caught measles infection, vaccination introduces your body to a form of the live virus that has been greatly weakened in a laboratory. This allows you to build immunity against the disease without getting sick, as well as avoiding the horrible complications that can accompany measles infection.

It means you avoid the immune suppression that leaves you vulnerable to other infections, too. Vaccination doesn’t only protect you against getting measles, but also prevents other infections from taking hold while you’re in a state of measles-induced immune system suppression.

Why lots of people need to be protected

Because of measles’ extreme contagiousness, high vaccination rates are incredibly important. At least 95 per cent of the population need to be immune to measles in all communities in order to prevent its spread to those who are still susceptible, such as the very young, the immunocompromised, and anyone else who is unable to receive the vaccine.

Australia’s overall vaccination rate has been high enough that local measles has been declared eliminated from our own population: when new cases are brought into the country from overseas, outbreaks are generally well-contained and don’t spread far or last for long because of the immune buffer resulting from high vaccination coverage. However, the recent rise in measles cases shows that measles will remain the ‘canary in the coal mine’, finding any pockets in the community where immunity is not as strong as it could be.

Choosing not to vaccinate against measles means denying yourself, or someone that you love, the tools to defend against a disease that can cause life-threatening complications or even death. We all want to do everything in our power to keep ourselves and our loved ones healthy. Full vaccination with two doses of the MMR vaccine is the best way to prevent the consequences of a potentially serious illness.

This is part of a series of articles produced by The Australian Academy of Science, funded by the Australian Government.

This article was first published on Australia’s Science Channel, the original news platform of The Royal Institution of Australia.