Almost everyone should get vaccinated against vaccine-preventable illnesses, unless you have a weakened immune system or your healthcare provider recommends that you don’t. If you have a weakened immune system, live vaccines can be dangerous. If you’re pregnant, live vaccines could pose a risk to the fetus. Ask your healthcare provider if it’s safe for you to get vaccines.
You usually get vaccines:
You can find out what vaccines are recommended for you based on age and risk factors from the Centers for Disease Control and Prevention/CDC (in the U.S.), the National Health Service/NHS (in the U.K.) or your local public health authority.
Vaccines are often given as shots, but there are also oral and nasal vaccines.
Some vaccines require more than one dose to be effective. This can be because:
An immunization schedule is a recommendation on when you should get vaccinated for each vaccine-preventable illness, usually based on age. You can find immunization schedules through the CDC (in the U.S.), the NHS (in the U.K.) or your local public health authority. The schedule will tell you how many doses you need and how far apart to get the doses.
Most people get vaccinated so they won’t get sick with an infectious disease. Viruses and bacteria can not only make you feel terrible, but they can also cause serious complications, which can be life-threatening or long-lasting. But vaccines can also help protect the people around you — your loved ones, people in your community and around the world — by stopping the spread of an illness.
There are personal, community and global benefits of vaccination. Vaccines:
Infants and people with weakened immune systems are particularly vulnerable to getting seriously ill with infectious diseases. But they aren’t yet vaccinated or can’t get vaccinated against them. The more people close to them and in their community who are vaccinated, the less likely it is they’ll get infected.
If enough people are vaccinated, a disease will stop spreading and eventually no one will get sick with it anymore. When there aren’t any more cases of a specific illness in an area, it’s considered eliminated. But as long as there are some cases still in the world, if enough people stop getting vaccinated, the disease can come back.
When there aren’t any more cases of a specific illness in the entire world, it’s considered eradicated. Smallpox is an example of a human disease that’s been eradicated through vaccination.
For people without underlying health issues, the main risks of getting vaccinated are side effects or an allergic reaction.
If you have a weakened immune system or underlying health issues, live vaccines could make you sick. Ask your healthcare provider before getting vaccinated.
Like every medication, vaccines go through a series of safety tests. Thousands of volunteers receive a vaccine before it’s released to the public. Different doses are tested to find the right balance between how well it works and how serious the side effects are. Vaccines don’t get approved if they don’t work without causing serious reactions.
No matter which type of vaccine is used, the active ingredients are broken down in your body or destroyed by your immune system within a few days. This means vaccines can’t cause long-lasting health effects.
Vaccine ingredients are tested to make sure that the amount of the ingredient you receive is safe. Most vaccines contain ingredients already found in your body or things you eat. For instance, aluminum salts, used as an adjuvant, are in drinking water and some medicines like antacids. Formaldehyde, used in making some vaccines, exists in small amounts in your body naturally (and even smaller amounts in any vaccine). Gelatin, used as a stabilizer, is in many foods.
Thimerosal, the ingredient most people worry about, has been studied extensively for safety. Studies show no evidence that thimerosal is harmful to humans. Thimerosal doesn’t contain the same kind of mercury that causes poisoning and it’s cleared from your body quickly. In the U.S., it’s currently only used in multidose vials of flu vaccine.
No, vaccines don’t cause autism spectrum disorder (ASD). A small study done in the late 1990s that linked the MMR vaccine to ASD has since been discredited. Numerous studies done around the world since then have found that vaccines don’t cause autism. These studies have compared hundreds of thousands of people based on whether or not they were vaccinated and whether or not they had a diagnosis of ASD. Even those at the highest risk of ASD are no more likely to be diagnosed after getting an MMR vaccine than those who aren’t vaccinated.
No, vaccines can’t alter your DNA. Viruses and bacteria used in vaccines are destroyed by your immune system, which gives you protection against future infections. DNA and mRNA in vaccines don’t interact with your DNA and can’t do anything to change it.
If you have a healthy immune system, you can’t get a disease from a vaccine. If you have a compromised immune system, there’s a risk that you could get sick from a live vaccine. Inactivated vaccines, subunit vaccines and mRNA vaccines don’t have anything in them that could actually infect you. Live vaccines use a weakened form of a virus or bacteria that can’t make healthy people sick. The side effects you experience from vaccines are reactions from your immune system making antibodies.
Talk to your healthcare provider about what vaccines they recommend for you. If you’re pregnant, are being treated for an ongoing health condition or have a weakened immune system, ask your provider which vaccines are safe for you.
Contact your provider if you have any serious side effects after getting vaccinated.
If you’ve never known anyone who’s had a particular disease, you might wonder why you should bother getting vaccinated for it. But think of it this way: The disease is uncommon because so many people have gotten vaccinated against it.
When enough people stop getting vaccinated or stop getting their kids vaccinated because they think they can’t get sick, the disease can begin spreading again. For instance, if someone who’s not vaccinated travels to a place where the disease still exists, they can bring it back to their community and cause an outbreak. Large outbreaks can overwhelm hospitals and put infants, older adults and people with weakened immune systems at risk for life-threatening illnesses. Instances of polio and measles in the U.S. in recent years are examples of how outbreaks of disease can still happen if not enough people are vaccinated.
Vaccines don’t always fully prevent you from getting sick, but that doesn’t mean they didn’t work. Some reasons you might still get sick with a disease you were vaccinated for include:
Vaccines can take decades to go from a theory in a lab to testing in humans. Once they get to human testing, it can take months or years to get approved. Vaccines go through the same testing that other drugs do. Several trials are required to find the safest dose of the vaccine, how effective it is and whether there are serious side effects.
There’s evidence that people have been inoculating against diseases since as early as the 10th century, but the first modern version of a vaccine was for smallpox. Back in the 1700s, people started noticing that people who had cowpox didn’t get smallpox. They found ways to infect people with the pus from cowpox to prevent them from getting smallpox, a much more serious illness. From there, Edward Jenner created the first vaccines for smallpox. Smallpox no longer exists (it’s eradicated) because of vaccinations.
Vaccines have rid the world of smallpox and greatly reduced the threat of polio, measles and other diseases. Vaccines have saved millions of lives — from your friends and neighbors to people around the world.
The science of today’s vaccines may seem complex and even a little scary. But it’s based on knowledge we’ve had for centuries about how our bodies fight disease. Vaccines show your body the tools it needs to stop the battle before it starts.
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Last reviewed on 09/07/2022.
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