COVID booster shots for the most vulnerable: Who can get them and why?


Medical studies show that vaccines still provide strong protection against the most dangerous effects of COVID-19 and its variants. 

Sara Tew/CNET

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After a third dose of the Moderna and Pfizer vaccines was authorized for some immunocompromised people by the US Food and Drug Administration on Thursday night, the Centers for Disease Control and Prevention recommended that people with “moderately to severely” compromised immune systems get an extra dose of an mRNA vaccine.

“CDC does not recommend additional doses or booster shots for any other population at this time,” the agency said in its new guidance Friday.

Because the CDC gave its stamp of approval, people who qualify can now go out and get their third dose of a COVID-19 vaccine. The list of immunocompromised people who can get a third shot includes solid organ transplant recipients or people who have an “equivalent level of immunocompromise” and who have a reduced ability to fight off infections, making them more vulnerable to the coronavirus. Booster authorization hasn’t been expanded more broadly to those with other chronic medical conditions, but that might be next. “We believe, sooner or later, you will need a booster for durability of protection,” Dr. Anthony Fauci said during a White House briefing Thursday. 

What does all this mean in the US? Read on for what we know about COVID-19 booster shots today, including why they’re needed, how they relate to breakthrough infections and what the controversy has been surrounding third shots. We’ll be updating this as new information is released.

Who’s eligible to receive COVID booster shots?

The CDC recommendation is for an additional dose of the two-shot vaccine for certain immunocompromised people, which is a small group. Within that category, the recommendation is for those 18 and older for the Moderna vaccine, and 12 and older for the Pfizer vaccine. The FDA didn’t authorize an additional dose to the Johnson & Johnson vaccine, and the CDC doesn’t recommend a second dose for immunocompromised people who got the one-shot vaccine, because of a lack of data.

About 3% of US adults are immunocompromised, according to the CDC, but research suggests they account for about 44% of hospitalized breakthrough cases of COVID-19. Not only are they more likely to get very ill from COVID, they also have a lower antibody response to vaccines and are at a higher risk of transmitting the virus. 

Those with other conditions, like diabetes and heart disease, aren’t advised to get a booster, at least for now. Here’s a list of people the CDC recommends get an extra dose (if they got the Pfizer or Moderna vaccine): 

  • Those with advanced or untreated HIV infection.
  • Cancer patients and transplant recipients who are taking certain immunosuppressive drugs.
  • Those receiving active cancer treatment for tumors or cancers of the blood.
  • Those with moderate or severe primary immunodeficiency. 
  • Patients being treated with high-dose corticosteroids or other drugs that may suppress immune response. 
  • People who received a stem cell transplant within the last two years and are taking certain drugs. The CDC says to talk to your medical provider about your health condition and whether a third shot is appropriate. 

If you’re unsure if you’re qualified, the CDC says to talk to your medical provider about your health condition and whether a third dose is appropriate. 

What’s behind the need for COVID booster shots?

Calling the eradication of the COVID-19 virus “unlikely,” a UK scientific advisory group says (PDF) there’s a “realistic possibility” that a variant will emerge that is resistant to the current battery of vaccines. Governments, public health organizations and vaccine makers are all tracking developments in coronavirus variants like delta and lambda, hoping to answer the question if booster shots targeting new variants will be needed soon among the general population.

Currently in the US, “breakthrough” coronavirus cases caused by the dominant delta variant amount to less than 1% of people who are fully vaccinated. Both the Moderna and Pfizer vaccines have proved to be more than 90% effective against hospitalizations and death. Nonetheless, the CDC’s study shows that vaccinated people can both contract the highly contagious delta variant and spread it. According to a widely reported internal CDC memo, the delta variant spreads as easily as chicken pox, which is considered more contagious than the flu but less contagious than measles. 

The surge in new COVID-19 cases is primarily affecting unvaccinated people and causing community spread, and in turn, prompting the return of mask mandates and guidance in hard-hit areas, even for people who have full vaccine protection. The debate over mask use and vaccine boosters underscores how scientists and other health experts continue to grapple with the uncertainties of COVID-19.

What’s the controversy over booster shots?

Israel has been administering third doses of the vaccine to those 60 and older, and the UK plans to do the same in September. However, this is resulting in a backlash among countries that are struggling to deliver first and second shots to residents. 

World Health Organization Director-General Tedros Adhanom Ghebreyesus called for a “moratorium” on booster shots in high-income countries, citing the global disparity in vaccine distribution. Of the 4 billion doses administered globally, 80% have gone to high- and upper-middle income countries that make up less than half the world’s population, he said. 

“We cannot accept countries that have already used most of the global supply of vaccines using even more of it, while the world’s most vulnerable people remain unprotected,” Tedros said. “We call on vaccine producers to prioritize Covax,” Tedros said, referring to the world’s COVID-19 vaccine distribution program.

What’s the difference between boosters and a new COVID vaccine?

Like Moderna’s, Pfizer’s current two-dose vaccine provides powerful and effective protection against all known variants of COVID-19, including the delta variant, according to ongoing studies and self-reported statistics. But Pfizer also announced in July that a third dose of its vaccine is currently under development. The company said its own research showed a booster shot of its current vaccine increased antibody levels five to 10 times higher over its two-dose shots, noting that its results haven’t been published or peer reviewed. 

Pfizer said it believes the level of protection the first two doses of its vaccine provide can gradually decrease over time, and a third booster dose may be needed “within six to 12 months” after a person is fully vaccinated with the first two doses. However, though a booster shot would complement the two doses of its existing vaccine, Pfizer is also separately working on a new vaccine formulation targeting the delta variant.

What’s happening with Johnson & Johnson boosters?

At this time, the FDA and CDC haven’t extended the authorization and recommendation for an additional dose to the Johnson & Johnson vaccine, citing insufficient data. 

Residents in San Francisco who received Johnson & Johnson’s one-dose COVID vaccine were given the green light to get a supplemental dose of an mRNA vaccine, though it still isn’t recommended by the city’s health department. Dr. Grant Colfax, San Francisco’s health director, said there isn’t conclusive evidence that getting a dose of Pfizer or Moderna benefits those who got the J&J shot, but there’s also no evidence to show it’s harmful, the San Francisco Chronicle reported. “If people received the Johnson & Johnson and are requesting a second shot, we will accommodate them, but our policy has not changed,” Colfax said.

San Francisco’s decision to legitimize Johnson & Johnson vaccine recipients getting an mRNA vaccine comes in light of a small study that suggests the vaccine isn’t nearly as effective against the delta variant as the other vaccines. (Another study suggests that Johnson & Johnson remains effective, and the drug-maker continues to assert that the vaccine is effective.) 

Biden press conference

The Biden administration says booster shots would be free.

Screenshot by Corinne Reichert/CNET

Would the booster shot be free?

The current one-dose vaccine shot from Johnson & Johnson and two-dose versions from Moderna and Pfizer are free to anyone who wants to get vaccinated. According to the Biden administration, COVID-19 booster shots will also be free, if and when they’re approved.

Is it OK to mix and match COVID vaccines?

The CDC now says a third dose of a different vaccine brand is permitted if same-dose types aren’t available.

Other global health agencies and countries are testing administered vaccines from two different manufacturers. In the UK, for example, a recent study found that those who received a first dose of the AstraZeneca vaccine and a second of Pfizer had a higher immune response than those who received two doses of the AstraZeneca vaccine.

While we watch how the situation develops, here’s what we know about the delta variant, more about COVID-19 boosters and info on whether you need to continue to wear a mask.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.