COVID-19 vaccine

Is It Time to Get a COVID-19 Booster? Which One? What You Need to Know

Who is eligible — and when — differs depending on which vaccine you got first

NBC Universal, Inc. Your questions about COVID vaccine booster shots, answered.

Millions more Americans just became eligible for COVID-19 boosters but figuring out who's eligible and when can be confusing — and adding to the challenge is that this time around, people can get a different type of vaccine for that extra dose.

A number of factors, including the vaccine you started with and when your last dose was, help determine when you qualify. Just like the initial shots, boosters are free and will be available at pharmacies, doctor offices and clinics.

Here are some things to know:

Do you need to get a COVID-19 booster shot?

People who are fully vaccinated still have strong protection against hospitalization and death from COVID-19.

But immunity against milder infections can wane over time, and the extra-contagious delta variant is spreading widely. U.S. health authorities want to shore up protection in at-risk people who were vaccinated months ago — although the priority remains getting the unvaccinated their first shots.

Which vaccines have been approved for boosters?

All three vaccines authorized for use in the U.S. are now approved for boosters. Pfizer boosters began last month and this week the government cleared extra doses of the Moderna and Johnson & Johnson vaccines, too.

Who is eligible to get a Pfizer booster shot and when?

If you got Pfizer's two-dose vaccine, you’re eligible for a booster shot six months after your last dose if you belong to one of the qualifying groups:

  • 65 years or older
  • 18 and older who lives in a long-term care setting that puts you at higher risk of either severe illness or exposure to the coronavirus.
  • 18 and older who has an underlying medical condition
  • 18 and older who works in a job that puts you at a higher risk of either severe illness or exposure to the coronavirus.

The main goal is to give an extra layer of protection to older and medically fragile people. But factors such as jobs are included because health care workers, for example, are regularly exposed to the coronavirus and can’t come to work with even the mildest of infections.

Who is eligible to get a Moderna booster shot and when?

If you received Moderna's two-dose vaccine, you’re eligible for a booster shot six months after your last dose if you belong to one of the qualifying groups:

  • 65 years or older
  • 18 and older who lives in a long-term care setting that puts you at higher risk of either severe illness or exposure to the coronavirus.
  • 18 and older who has an underlying medical condition
  • 18 and older who works in a job that puts you at a higher risk of either severe illness or exposure to the coronavirus.

Who is eligible to get a J&J booster shot and when?

Anyone who got a J&J shot at least two months ago is eligible — regardless of age or other factors.

So, what counts as a qualifying underlying health condition?

According to the CDC, people of any age with the following conditions are more likely to get severely ill from COVID-19:

  • Cancer
  • Chronic kidney disease
  • Chronic lung diseases, including COPD, asthma (moderate-to-severe), interstitial lung disease, cystic fibrosis, and pulmonary hypertension
  • Dementia or other neurological conditions
  • Diabetes (type 1 or type 2)
  • Down syndrome
  • Heart conditions (such as heart failure, coronary artery disease, cardiomyopathies or hypertension)
  • HIV infection
  • Immunocompromised state (weakened immune system)
  • Liver disease
  • Overweight and obesity
  • Pregnancy
  • Sickle cell disease or thalassemia
  • Smoking, current or former
  • Solid organ or blood stem cell transplant
  • Stroke or cerebrovascular disease, which affects blood flow to the brain
  • Substance use disorders

Why are there different recommendations for the different vaccines?

A single shot of the J&J vaccine was found in clinical trials to have a 74% efficacy in the U.S., which is less effective than the over 90% efficacy rate of the two doses of Moderna or Pfizer vaccines.

However, a second dose of J&J's shot results in performance similar to that of the mRNA vaccines, boosting protection from symptomatic infection to 94% when administered two months after the first dose in the United States, according to company data released Sept. 21.

Because of this, health authorities decided it was important for the J&J recipients to achieve a similar level of protection and authorized it for a broader group.

As for the timing, J&J simply had tested more people with a two-month booster than one at six months. For recipients of Moderna or Pfizer vaccinations, there's not clear data that everybody needs another dose but immunity against infection in at least some people appeared to wane around six months.

What if I don’t want to wait six months?

Timing matters because the immune system gradually builds layers of defenses over months, and letting that response mature improves the chances another, later dose will provide even stronger protection. Experts agree that getting a booster too soon can actually reduce the benefit.

A CDC panel of advisers voted to recommend a booster shot of Pfizer’s COVID-19 vaccine to people over 65 and high risk Americans, backing a similar decision by the FDA.

What does mixing and matching booster doses mean?

It means a booster that's different than your original vaccination. That gives flexibility in situations such as nursing homes where health workers on booster visits may bring only one type. It also gives people at risk of a rare side effect linked to one kind of vaccine the option of switching to a different shot.

Should I choose a different vaccine for my booster shot?

The CDC didn't recommend that people switch but left open the option.

Preliminary results of a government study found an extra dose of any vaccine triggered a boost of virus-fighting antibodies regardless of what shots people got to begin with.

The National Institutes of Health study on "mixing and matching" COVID vaccines showed recipients of Moderna or Pfizer's original vaccines could easily swap third doses; the results were about the same.

However, for study participants who originally got a J&J vaccination, the Moderna and Pfizer shots appeared to offer a stronger boost . But researchers cautioned the study was too small to say one combination was better than another, and only measured antibodies when the immune system forms additional layers of protection.

What are the most common side effects reported after a booster of Moderna, J&J or Pfizer?

The most common side effects reported after getting a third shot of an mRNA vaccine, the type made by Moderna and Pfizer, were pain at the injection site, fatigue, muscle pain, headache and fever, followed by chills and nausea, according to CDC data, based on submissions to the agency's text messaging system v-safe and the Vaccine Adverse Event Reporting System.

Side effect rates were similar to those seen after the second dose of an mRNA vaccine, the CDC reports.

The data available for J&J was more limited, but people reported fever, fatigue and headache after receiving a second dose of that vaccine, according to the agency.

Do I need a booster to still be considered fully vaccinated?

No, the CDC says people still are considered fully vaccinated starting two weeks after the second dose of the Moderna or Pfizer vaccines, or the single-dose J&J shot.

Will this be my last booster?

Nobody knows. Some scientists think eventually people may get regular COVID-19 shots like we get annual flu vaccinations but researchers will need to study how long protection from the current boosters lasts.

The Associated rPress/NBC