How do vaccines work?

How does a vaccine work?

Vaccinations are our best protection against infections that, in the past, have killed many people. When we receive a vaccine, we become immune – or protected – from that specific infection. Because many of the germs that cause vaccine-preventable infections are still in our environment, we need to stay up to date with vaccinations to remain protected.

Vaccines work by teaching your body to recognize specific dangerous pathogens so your immune system is prepared to fight off that infection in the future. Vaccines introduce small parts of germs that are weakened or dead, collectively called antigens, to our body. These antigens act to trigger the body’s natural immune response but without causing illness.

How vaccines protect against pathogens

In response to a vaccine antigen, specialized immune system cells called T and B lymphocytes, or T and B cells, become activated so that if we are infected by the germ at a later time, our body’s immune defence system will recognize the invaders and protect us.

Vaccines, then, are much safer than developing immunity through being infected with a germ.

B-cells produce antibodies, which are proteins that bind to antigens. These antibodies tag the virus or bacteria and alert immune cells to their presence, so they can be gobbled up and disposed of. Antibodies can also neutralize pathogens directly by binding to the antigens in a way that blocks their activity, preventing them from making us sick. T-cells, on the other hand, attack and destroy infected cells in our body to stop the infection from spreading. After a vaccine, these memory cells stay circulating in the body, making it easier for the body to fight off the live virus or bacteria if you are ever exposed.

Vaccines also frequently contain additives, called adjuvants, to the vaccine itself that can help promote a stronger immune response, making the vaccines more effective for a longer period of time.

Not all vaccines are the same

The immune system’s response and memory can vary depending on the pathogen and the type of vaccine used, which is why sometimes we need to get more than one dose of a vaccine, or even get regular booster shots to remind our immune system of the organism. Some viruses, like the flu, change each year, and annual differences in the type of virus circulating in the population require a new vaccine each time to protect against the most common strains for that season.

Vaccines protect our community, too

Within a community, vaccines can create herd immunity. Not everyone has an immune system that can mount a proper immune response. Some people — particularly infants, the elderly, and the immunocompromised — can’t get certain vaccines and are especially vulnerable to severe illness when they’re exposed to live pathogens. If enough healthy people get vaccinated, it makes it almost impossible for a disease outbreak to occur because the disease can’t establish itself in enough hosts to spread through the population. This protects the most vulnerable among us, even if they can’t get a vaccine themselves.

This is why doctors recommend staying up to date on your vaccinations, including an annual flu shot, to protect yourself and your loved ones from preventable illnesses.

Watch part two: What are the different types of vaccines?

Watch part three: How are vaccines made?

Watch part four: How does the FDA approve vaccines?