Vaccines to prevent coronavirus disease 2019 (COVID-19) are perhaps the best hope for ending the pandemic. But as the U.S. Food and Drug Administration (FDA) continues authorizing emergency use of COVID-19 vaccines, you likely have questions. Find out about the benefits of the COVID-19 vaccines, how they work, the possible side effects and the importance of continuing to take infection prevention steps.
A COVID-19 vaccine might:
Currently, several COVID-19 vaccines are in clinical trials. The FDA will review the results of these trials before approving COVID-19 vaccines for use. But because there is an urgent need for COVID-19 vaccines and the FDA's vaccine approval process can take months to years, the FDA will first be giving emergency use authorization to COVID-19 vaccines based on less data than is normally required. The data must show that the vaccines are safe and effective before the FDA can give emergency use authorization. Vaccines with FDA emergency use authorization include:
Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use messenger RNA (mRNA). Coronaviruses have a spike-like structure on their surface called an S protein. COVID-19 mRNA vaccines give cells instructions for how to make a harmless piece of an S protein. After vaccination, your cells begin making the protein pieces and displaying them on cell surfaces. Your immune system will recognize that the protein doesn't belong there and begin building an immune response and making antibodies.
The Janssen/Johnson & Johnson COVID-19 vaccine is a vector vaccine. In this type of vaccine, genetic material from the COVID-19 virus is inserted into a different kind of weakened live virus, such as an adenovirus. When the weakened virus (viral vector) gets into your cells, it delivers genetic material from the COVID-19 virus that gives your cells instructions to make copies of the S protein. Once your cells display the S proteins on their surfaces, your immune system responds by creating antibodies and defensive white blood cells. If you become infected with the COVID-19 virus, the antibodies will fight the virus.
Viral vector vaccines can't cause you to become infected with the COVID-19 virus or the viral vector virus. Also, the genetic material that's delivered doesn't become part of your DNA.
The COVID-19 vaccines were developed based on the S protein before it contained the mutations identified in the variants. While research suggests that COVID-19 vaccines have lower efficacy against the variants, the vaccines still appear to provide protection against severe COVID-19. Further research is needed.
In addition, vaccine manufacturers are also creating booster shots to improve protection against variants.
No. The COVID-19 vaccines currently being developed in the U.S. don't use the live virus that causes COVID-19.
Keep in mind that it will take a few weeks for your body to build immunity after getting a COVID-19 vaccination. As a result, it's possible that you could become infected with the virus that causes COVID-19 just before or after being vaccinated.
A COVID-19 vaccine can cause mild side effects after the first or second dose, including:
You'll likely be monitored for 15 minutes after getting a COVID-19 vaccine to see if you have an immediate reaction. Most side effects happen within the first three days after vaccination and typically last only one to two days.
A COVID-19 vaccine may cause side effects similar to signs and symptoms of COVID-19. If you've been exposed to COVID-19 and you develop symptoms more than three days after getting vaccinated or the symptoms last more than two days, self-isolate and get tested.
You might be having an allergic reaction to a COVID-19 vaccine if you experience these signs within four hours of your first vaccine dose:
If you have any signs of an allergic reaction, get help right away. Tell your doctor about your reaction, even if it went away on its own or you didn’t get emergency care. This reaction might mean you are allergic to the vaccine. You might not be able to get a second dose of the same vaccine. However, you might be able to get a different vaccine for your second dose.
It isn’t recommended that you take a pain medication before getting a COVID-19 vaccine to prevent possible discomfort. It’s not clear how these medications might impact the effectiveness of the vaccines. However, it’s OK to take this kind of medication after getting a COVID-19 vaccine, as long as you have no other medical reason that would prevent you from taking it.
Because COVID-19 vaccines clinical trials only started in the summer of 2020, it’s not yet clear if these vaccines will have long-term side effects. However, vaccines rarely cause long-term side effects.
If you’re concerned, in the U.S., safety data on COVID-19 vaccines will be reported to a national program called the Vaccine Adverse Event Reporting System. This data is available to the public. The Centers for Disease Control and Prevention (CDC) has also created v-safe, a smartphone-based tool that allows users to report COVID-19 vaccine side effects.
In the U.S., the CDC has recommended that the COVID-19 vaccines first be offered to:
Guidelines for who will be vaccinated first also vary by state in the U.S. Consult your local health department for the latest information on how and when you can receive a vaccine.
If you have a history of severe allergic reactions not related to vaccines or injectable medications, you may still get a COVID-19 vaccine. You should be monitored for 30 minutes after getting the vaccine.
If you've had an immediate allergic reaction to other vaccines or injectable medications, ask your doctor if you should get a COVID-19 vaccine. If you’ve ever had an immediate or severe allergic reaction to any ingredient in a COVID-19 vaccine, the CDC recommends not getting that specific vaccine.
If you have an immediate or severe allergic reaction after getting the first dose of a COVID-19 vaccine, don't get the second dose. However, you might be able to get a different vaccine for your second dose.
Yes, if you have an existing health condition you can get a COVID-19 vaccine — as long as you haven't had an allergic reaction to a COVID-19 vaccine or any of its ingredients. But there is limited information about the safety of the COVID-19 vaccines in people who have weakened immune systems or autoimmune conditions.
There is no research on the safety of COVID-19 vaccines in pregnant or breastfeeding women. However, if you are pregnant or breastfeeding and part of a group recommended to get a COVID-19 vaccine, you may choose to get the vaccine. Talk to your health care provider about the risks and benefits.
There is no COVID-19 vaccine yet for children under age 16. Several companies have begun enrolling children as young as age 12 in COVID-19 vaccine clinical trials. Studies including younger children have also begun.
Getting COVID-19 might offer some natural protection or immunity from reinfection with the virus that causes COVID-19. But it's not clear how long this protection lasts. Because reinfection is possible and COVID-19 can cause severe medical complications, it's recommended that people who have already had COVID-19 get a COVID-19 vaccine. If you’ve had COVID-19, you might delay vaccination until 90 days after your diagnosis. Reinfection with the virus that causes COVID-19 is uncommon in the 90 days after you are first infected.
After getting a COVID-19 vaccine, the CDC recommends that it’s OK for fully vaccinated people to:
You are considered fully vaccinated 2 weeks after you get a second dose of an mRNA COVID-19 vaccine or 2 weeks after you get a single dose of the Janssen/Johnson & Johnson COVID-19 vaccine.
However, vaccinated people should continue to take safety precautions, such as wearing a mask and avoiding close contact (within about 6 feet, or 2 meters) with others, when they are:
Keep in mind that if you’re fully vaccinated from COVID-19, your risk of getting COVID-19 might be low. But if you become infected, you might spread the COVID-19 virus to others even if you don’t have any signs or symptoms of COVID-19.
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