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Los Angeles County over the weekend started administering third doses of the Pfizer and Moderna COVID-19 vaccines to people with weakened immune systems.

Studies have shown that some immunocompromised people don’t build enough protection after receiving two vaccine doses. Because of this, the U.S. Food and Drug Administration and Centers for Disease Control and Prevention approved giving an additional dose to protect the small, vulnerable group.

L.A. County on Saturday released information about who can get the additional shot and how to go about getting it. Here’s what we know about who’s eligible, when a third shot can be given and how the process of getting another dose works.

Who can get a 3rd dose?

As of now, booster doses are not recommended for the general public.

L.A. County is advising residents with weakened immune systems to talk to their doctors about the need to get another dose and the best time to do it based on their treatment plans — especially for those about to start or restart immunosuppressive treatment.

People approved to receive an additional dose include people who have:

  • Been receiving active cancer treatment for tumors or cancers of the blood
  • Received an organ transplant and are taking medicine to suppress the immune system
  • Received a stem cell transplant within the last two years
  • Are taking medicine to suppress the immune system
  • Moderate or severe primary immunodeficiency, such as DiGeorge syndrome or Wiskott-Aldrich syndrome
  • Advanced or untreated HIV infections
  • Active treatment with high-dose corticosteroids or other drugs that may suppress the immune response

When can you get the 3rd dose?

Immunocompromised people can get a third shot of an mRNA COVID-19 vaccine at least 28 days after they got their their second dose.

How do you get the 3rd dose?

Third doses are available at vaccination sites that currently offer Pfizer or Moderna vaccines. Patients can also ask about getting vaccinated at their doctor’s facility.

L.A. County residents can search here for a nearby location that offers the same kind of vaccine they took previously if they can’t get it at their doctor’s office.

Eligible people will have to self-attest that they are immunocompromised using this form in English or Spanish.

Does it have to be the same vaccine for all 3 shots?

L.A. County health officials say the same type of vaccine should be used for the third shot, if possible.

If that is not possible, receiving a third dose with another mRNA vaccine is acceptable.

What about people who got J&J?

A follow-up dose is not currently recommended for those who got the Johnson & Johnson vaccine. The FDA is still looking into the effectiveness of that vaccine in immunocompromised people.

The CDC says there is not enough data to determine whether immunocompromised people who received the Johnson & Johnson’s vaccine also have an improved antibody response following an additional dose of the same vaccine.

What side effects can you expect after the 3rd dose?

There is limited information about the risks of receiving an additional dose, according to the CDC.

So far, reactions reported after the third dose were similar to those of the other two dose series.

Most commonly reported side effects include fatigue and pain at injection site. And overall, most symptoms were mild to moderate, according to CDC.

As with the two-dose vaccine series, officials say serious side effects are rare, but may occur.

What about the general public?

Booster shots are are not recommended for the general public, but that could change.

U.S. health authorities are expected to recommend an extra dose of the vaccine for all Americans eight months after they get their second shot as early as Wednesday, anonymous sources told The Associated Press.