Vaccination

Vaccines protect you (and everyone around you) from highly infectious and potentially deadly pathogens (disease-causing organisms such as bacteria and viruses) without you needing to be exposed to the actual pathogen. Medical historians consider vaccines one of the most important advances in medicine, and vaccines save the lives of millions of people around the globe each year.

How vaccines work

Vaccines allow your body to produce infection-fighting cells and pathogen-specific antibodies, which are the molecules that remain in your immune system and recognize and attack pathogens. A vaccine mimics an infection by exposing your immune system to a weakened or dead pathogen, allowing the system to recognize this pathogen and build up protection against it. Then, if you are exposed to the real pathogen, you are protected, or at least much less likely to acquire that particular disease and experience complications from it.

It takes up to two weeks for you to be fully protected after getting a vaccine because it takes that long for pathogen-specific antibodies to be produced. If you are exposed to a pathogen before or right after getting the vaccine for it, you may get sick simply because your immune system hasn't had time to produce enough antibodies.

You may have minor symptoms after getting a vaccine, such as aches and fever, that feel like you're getting sick, but you aren't (vaccines almost never cause the illness they aim to protect you from). The symptoms you feel are your immune system responding to the vaccine and producing protection against the pathogen.

What is herd immunity (community immunity)?

Vaccination not only protects yourself, it also protects everyone around you. If enough people get vaccinated (between 75–94% of the population, depending on the disease), it will likely protect those who don't get vaccinated. When enough people are vaccinated against the disease, a pathogen has a hard time being passed from person to person and can't spread easily through a community.

Herd immunity is especially important to those who can't get vaccinated because they are too young, too old, too sick, or have an allergy or chronic condition that prevents them from receiving a specific vaccine. It can even protect the few people who have been vaccinated but didn't have a strong immune response to them, leaving them vulnerable to disease.

Why should I get vaccinated?

Protecting yourself and your community aren't the only reasons to vaccinate. As more people in a region vaccinate, the diseases they protect against become rarer; in fact, if the vast majority of people immunize for long enough, diseases can be eradicated from their region. Smallpox, for example, was eradicated worldwide.

On the flip side, if we stop vaccinating, we make ourselves and our communities much more vulnerable to diseases and epidemics.

What are the side effects from vaccines?

Like any medicine, vaccines can cause side effects, but they are usually mild (low-grade fever, sore throat, soreness around the injection site) and go away a few days after getting vaccinated. However, there is an extremely small chance you could have a more serious rare side effect, such as a severe allergic reaction, other serious injury, or death.

The anti-vax movement

Outbreaks can happen when people hesitate or refuse to vaccinate themselves or their kids (usually called being "vaccine hesitant" or "anti-vax"). When an entire community has low enough vaccination rates, outbreaks can occur because the pathogen can circulate, spreading from person to person.

An infamous anti-vax example involves the measles, mumps, and rubella (MMR) vaccine. The false link between MMR vaccination in children and the development of autism was made by discredited former British doctor Andrew Wakefield in a now retracted Lancet article published in 1998. But the damage was done; its publication sparked a large multinational anti-vax movement that has lowered immunity coverage in certain areas, which act as breeding grounds for recent measles outbreaks.

Since that infamous paper was published, researchers have studied the possible link between MMR vaccination and autism in millions of children around the world in multiple large-scale clinical studies. One such recent study look at over 657,000 children in Denmark born between 1999 through December 31, 2010. MMR vaccination was not found to increase the risk for autism, even in children susceptible to autism (those who had a sibling with autism or other autism risk factors). This adds even more evidence to support other large-scale studies that also did not find a connection between MMR vaccination and autism.

The World Health Organization declared the anti-vaccine movement as one of the top ten threats to global human health in 2019.

Type of vaccines

Developing a vaccine against a pathogen depends on multiple factors, such as if it is a bacteria or virus, what part of it is infectious, and how the immune system responds to it. Therefore, there are many different kinds of vaccines:

• Live, attenuated: Contain live but weakened pathogens that don't cause serious disease in healthy people. These vaccines are extremely effective because they resemble infection with the live, full-strength pathogen, so they produce a robust immune response. However, because these vaccines contain live (though attenuated) pathogens, not everyone can receive them.
• Inactivated: Contain killed pathogens that produce immune responses without the risk of causing disease. Multiple doses are usually needed to build up or maintain protection.
• Subunit: Contain parts of the pathogens (called subunits) that the immune system can recognize and use to build protection against the entire pathogen. Side effects are less common because the entire pathogen is not present. People with weakened immune systems can receive these vaccines, but boosters are commonly needed to maintain protection.
•  Recombinant: Contain genetically engineered cells that express parts of the target pathogen that trigger the immune system to recognize and build protection against it. Side effects are less common because the entire pathogen is not present. People with weakened immune systems can receive these vaccines, but boosters are commonly needed to maintain protection. Conjugate: Combine a weak pathogen with a stronger one so that the immune system can recognize the weaker one, which wouldn't, on its own, provoke an immune response.
• Toxoid: Contains weakened bacterial toxins (called toxoids) that train the body to fight off the normal toxin without causing illness.
• Messenger RNA (mRNA): Uses messenger RNA to instruct ribosomes in immune cells to make a specific antigen, which is then recognized by the immune system to create antibodies. Messenger RNA vaccines are an important new strategy in the fight against emergent diseases including COVID-19, Zika virus disease, and Ebola virus disease.

When should I get vaccinated?

There are vaccines for over 20 different bacteria and viruses, with some vaccines having multiple different types, formulations, and dosing schedules. To help organize when you should get which vaccine, the CDC publishes vaccine schedules for children and adults. The children and adolescent (from birth to 18 years old) vaccine schedule can be found here: https://www.cdc.gov/vaccines/schedules/hcp/imz/child-adolescent.html.

The adult (18 years and older) vaccine schedule can be found here: https://www.cdc.gov/vaccines/schedules/hcp/imz/adult.html.

In general, the majority of routine vaccines are recommended to infants between birth and 18 months because their immune systems are still forming and encountering new bacteria and viruses. The ideal situation is to have a child be vaccinated before they come in contact with the bacteria or virus so they are protected once they do encounter the pathogen.

Some vaccines require multiple doses to achieve the best protection possible due to a variety of factors, including the type of vaccine it is (inactivated vaccines, for example), not enough antibodies being produced after the first dose to successfully fight off an infection, or protection wearing off over time.

A few vaccines need to be regularly administered throughout adulthood to maintain protection, such as the annual flu shot or the tetanus shot booster every 10 years. The specific flu viruses that are most prevalent in a season tend to change from year to year, which is why you need to get a new flu shot each year.