UPDATE: Since this article was published, the FDA cleared an additional vaccine option, a single-dose shot from Johnson & Johnson. Learn more here.

Now that COVID-19 vaccines are being administered nationwide, there are questions about who can safely get one. The Advisory Committee on Immunization Practices, an expert group that advises the Centers for Disease Control and Prevention, recommends the vaccine for people ages 16 years and older, but there are some exceptions. Here are the current CDC recommendations.

If you had COVID-19 and recovered

It’s currently unknown how long natural immunity may last after someone gets and recovers from COVID-19. While rare, there are case studies that show reinfection after just a couple months. Data shows the vaccine is safe and likely effective in people who previously had the virus. As a result, many experts say even if you’ve recovered from COVID-19, you should plan on getting the vaccine for extra protection. The CDC has not yet released a recommendation on when someone who’s previously had the virus should get vaccinated. But, current evidence suggests that reinfection is uncommon in the 90 days after initial infection, and it’s OK to delay vaccination until you’re near the end of this window, says the CDC.

If you actively have COVID-19

If you’re currently infected with the coronavirus, you must wait until you’ve recovered and meet the CDC’s criteria for when you can stop isolating at home. Once you’ve recovered, current evidence suggests that you’re not likely to get infected again in the 90 days after initial infection, and the CDC says it’s okay to delay vaccination until near the end of this period.

If you’ve been exposed to COVID-19

You should wait to get a vaccination until after your quarantine period has ended so that you can avoid potentially exposing others. There’s no data yet on whether a vaccine can prevent you from getting infected after you’ve been exposed to someone who has the coronavirus (but current evidence suggests it may not work that way).

It is known that the vaccine doesn’t protect you immediately. The Pfizer vaccine requires two doses, spaced three weeks apart, and it takes one to two weeks after the second dose before you’re considered fully vaccinated.

If, however, you live in a place where you could get exposed repeatedly over long periods of time (like a health-care setting, long-term care facility, correctional and detention facility, or homeless shelter) you may be vaccinated even if you’ve been exposed.

If you have allergies

The CDC breaks down allergy guidance into three categories: proceed with vaccination, vaccinate with caution, and don’t vaccinate.

Proceed with vaccination

You are cleared to get vaccinated if you have a history of the following allergies: Food, pets, insects, venom, environmental, latex, or other allergies not related to vaccines or injectable therapies; oral medications (including the oral equivalent of an injectable medication); nonserious allergies to vaccines or other injectables (for example, you haven’t had an anaphylactic response).

If you have a family history of anaphylaxis, or any other history of anaphylaxis that is not related to a vaccine or injectable therapy, you’re also cleared to get vaccinated.

If you have a history of severe allergic reaction, including a history of anaphylactic reactions, from any cause, it’s recommended that you wait for a 30-minute observation period after getting the vaccine to make sure you’re OK. If you have a history of allergic reactions (but not anaphylaxis, a 15-minute observation period is advised.

Vaccinate with caution

If you have a history of severe allergy or anaphylaxis to another vaccine (not the COVID-19 vaccine) or to an injectable therapy, the CDC advises talking to your health-care provider to assess your risk, and possibly delaying vaccination.

Don’t vaccinate

If you have a history of severe allergy or anaphylaxis to any component of the COVID-19 vaccine, you should not get vaccinated.

If you’re immunocompromised or take immunosuppressive medications

There’s not yet enough data to determine whether the vaccine is safe and effective for immunocompromised individuals, but the CDC says you may still get vaccinated if you don’t have another condition that would prevent you from doing so, such as a history of severe allergic reaction (see above). You should first talk with your health-care provider about the unknowns of the vaccine for immunocompromised populations, as well as the potential for a reduced immune response. Continue following other safety measures, like wearing a mask and social distancing, to protect yourself, says the CDC.

If you have an underlying medical condition

In Pfizer trials, the vaccine was shown to be as safe and effective for people with underlying medical conditions as for those without. You’re advised to get vaccinated if you don’t have another condition that would prevent you from doing so, such as a history of severe allergic reaction (see above).

If you’re pregnant

Based on current knowledge, experts believe the vaccines are unlikely to pose a risk for people who are pregnant. If you’re pregnant, the CDC advises talking with your doctor to help decide whether to get vaccinated. While this conversation may be helpful, it is not required prior to vaccination.

Pregnant people are not usually allowed to participate in vaccine studies, and they were not included in Pfizer’s vaccine trials. However, about two dozen people who got the vaccine became pregnant while participating in the studies. None reported complications. Future studies are planned.

When making a decision, you and your doctor should consider the level of community transmission, your personal risk of contracting the virus, the risks of COVID-19 to you and the potential risks to the fetus, the efficacy of the vaccine, the side effects of the vaccine, and the lack of data about the vaccine during pregnancy.

If you have a fever following vaccination, you may be advised to take acetaminophen, as fever has been associated with adverse pregnancy outcomes. Acetaminophen may be recommended for other side effects, too.

If you’re trying to become pregnant

You’re advised to get vaccinated if you’re among the groups whom it’s considered safe. You don’t need to avoid pregnancy after getting vaccinated.

If you’re lactating

There aren’t any studies yet on the effect of the vaccine on people who are lactating, and whether it affects milk production, excretion, or the infant. However, the Pfizer and Moderna vaccines are classified as messenger RNA vaccines (mRNA vaccines), a type of vaccine that’s not thought to pose a risk to breast-feeding infants. If you’re part of a vaccine priority group, such as those who work in health care, the CDC says you can get vaccinated if you wish.

If you’re a teenager (ages 16-17)

Adolescents ages 16 and 17 years old may be vaccinated if they wish. In this age group, Pfizer trials included 153 participants (out of nearly 44,000 total participants). No safety concerns appeared.

While data on safety and effectiveness for this age group is limited, the CDC says there’s no reason to believe the vaccine would work differently than it does for people who are 18 years and older.

If you’re younger than 16

The FDA granted an emergency use authorization for the vaccine to be used on people ages 16 and up, which means it’s not yet allowed to be administered to anyone younger. Vaccine makers are still in the early stages of testing the vaccines on children.

If you get vaccinated and have side effects

COVID-19 vaccines can cause side effects, but experts say you shouldn’t let that stop you from getting a vaccine if it’s considered safe for you to do so. For most people, if symptoms appear they will be mild or moderate, disappearing within a day or two. The most commonly reported side effects include pain and swelling around the injection site, headache, fatigue, fever, and muscle pain. Serious adverse reactions are rare.

Discomfort from fever or pain is normal. You may feel like you have the flu for a couple days, and that’s OK. But if redness or tenderness where you got the shot increases after 24 hours, or the side effects are worrying you or aren’t going away after a few days, call your doctor.

If you experience side effects after the first shot, you should still get the second shot, unless a vaccination provider or your doctor tells you otherwise.

The CDC and FDA encourage you to report any side effects to the Vaccine Adverse Event Reporting System (VAERS), a national system that helps the CDC monitor vaccine safety. When you get vaccinated, you should also receive an information sheet telling you how to enroll in v-safe, the CDC’s smartphone-based tool designed to check-in on your health after vaccination. Enroll to receive text messages directing you to surveys where you can report problems or side effects.

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Read more about vaccine guidelines and considerations from the CDC here.