COVID-19 vaccines are a critical tool to bring the pandemic under control. The risk of severe disease and death is much lower for vaccinated people compared to unvaccinated people. All authorized COVID-19 vaccines provide strong protection against serious illness and hospitalization due to COVID-19.

When we get a vaccine, it activates our immune response. This helps our bodies learn to fight off the virus without the danger of an actual infection. If we are exposed to the virus in the future, our immune system “remembers” how to fight it.

The Moderna and Pfizer-BioNTech vaccines use messenger RNA, or mRNA. mRNA vaccines do not contain a live virus. They give our bodies “instructions” for how to make and fight the spike-shaped proteins that will protect against a COVID-19 infection. While these vaccines use new technology, researchers have been studying them for decades.

Johnson & Johnson’s Janssen vaccine is a viral vector vaccine and does not contain a live virus either. It uses a harmless adenovirus to create a spike protein that the immune system responds to, creating antibodies to protect against COVID-19.

None of these vaccines can give you COVID-19. It takes time for your body to build immunity after vaccination, so you won’t have full protection until 2 weeks after your most recent dose.

COVID-19 vaccines provide strong protection from serious illness and hospitalization. Getting vaccinated and following CDC’s recommendations to take care of yourself and others is the best way to protect against COVID-19. CDC and other health experts are currently recommending mRNA vaccines (Pfizer-BioNTech and Moderna) as the preferred vaccines to protect against new variants.

The Pfizer-BioNTech vaccine (Comirnaty) is authorized for people ages 5 and older. It’s a messenger RNA, or mRNA, vaccine and includes two shots spaced 21 days apart. This vaccine was fully approved by the FDA for ages 16 and older in August 2021. It’s also available for ages 5 to 15 under emergency use authorization (and is being given in smaller doses to children age 5 to 11).

The Moderna vaccine is now fully approved by the FDA for people 18 years and over. It’s also an mRNA vaccine and includes two shots spaced 28 days apart. Clinical trials showed the Moderna vaccine also provides strong protection against serious illness.

For people who are unable or unwilling to receive an mRNA vaccine, the Johnson & Johnson Janssen vaccine is still authorized and available for people 18 years and over. It’s a viral vector vaccine and only requires one shot.

Staying up to date with COVID vaccines provides strong protection against severe disease and death when it comes to new variants. This includes booster shots at the appropriate time. Vaccines also reduce a person’s risk of getting the virus. But no vaccine is 100% effective and some fully vaccinated people will become infected and experience illness. This is called a breakthrough infection. When one happens, the vaccines still provide strong protection against serious illness and death.

The Delta variant and Omicron variant are extremely contagious — more than twice as contagious as the original virus. There have been more breakthrough cases with these new variants than the original virus, but vaccines and boosters are still effective at preventing severe illness and hospitalization from Delta and Omicron. Additionally, people who have not been fully vaccinated against COVID-19 are most at risk and more likely to transmit the virus to others.

COVID-19 vaccines are an effective tool to bring the pandemic under control. No vaccines are 100% able to prevent illness. Fortunately, the risk of serious illness, hospitalization, and death are all much lower if you’re vaccinated.

Recent data shows that vaccine effectiveness decreases over time. New variants are also even more infectious than the original virus. This leads to more breakthrough cases among those vaccinated. Vaccination still helps protect against serious illness and death. Because of this, CDC recommends that everyone age 12+ receive a booster shot at the appropriate time.

You may have short-term side effects after vaccination. These are normal and should go away in a few days.

You may feel soreness or experience some swelling in your arm. You may also feel tired, have a headache, fever, or chills. These symptoms do not mean you have COVID-19 — it’s not possible to get COVID-19 from the vaccine.

These side effects may impact your daily activities, but they shouldn’t last more than 2-3 days. If they continue or get worse, call your doctor, nurse, or clinic.

Even if you have these types of effects after your first shot, it’s important to make sure you get the second one, unless a vaccination provider or your doctor tells you not to get a second shot or you get the single dose vaccine. Ask your doctor if you have questions. Your body takes time to build immunity. You will not be fully protected against COVID-19 until 1-2 weeks after your final shot in your initial series or your booster shot.

In most cases, discomfort from fever or pain is normal. Contact your doctor or healthcare provider:

If the redness or tenderness where you got the shot increases after 24 hours

If your side effects are worrying you or do not seem to be going away after a few days

If you develop severe headache, abdominal pain, leg pain, or shortness of breath within the first three weeks.

If you get a COVID-19 vaccine and think you might have a severe allergic reaction after leaving the vaccination site, seek immediate medical care by calling 911. Learn more about COVID-19 vaccines and rare severe allergic reactions.