Some experts who had Johnson & Johnson's single-dose vaccine are now getting extra shots of Pfizer or Moderna to try to protect against the Delta variant

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  • Experts who got Johnson & Johnson's one-dose vaccine are topping up with a Pfizer or Moderna dose.

  • They did it for extra protection against the fast-spreading Delta coronavirus variant, they said.

  • The FDA and CDC don't recommend getting an extra shot, after a J&J vaccine or otherwise.

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Some experts who got Johnson & Johnson's one-dose vaccine are trying an extra shot of Moderna's or Pfizer's vaccine to try to protect against the fast-spreading Delta coronavirus variant.

Officials have not recommended getting a booster shot after J&J's vaccine or any other vaccine, and two experts said everyone should wait for more data.

Angela Rasmussen, a virologist at the University of Saskatchewan, tweeted on Tuesday that she got the Pfizer vaccine to "top off" the J&J vaccine she received in April.

Rasmussen said that the rise of the Delta variant in the UK - where more than 95% of new infections are caused by Delta - showed the "crucial importance" of getting as many people vaccinated as possible.

Rasmussen said that we don't know whether an extra vaccine dose after a J&J shot boosts protection against variants, and neither the Food and Drug Administration nor the Centers for Disease Control and Prevention has made any recommendations. But it was likely to work, she said, given that boosters work for nearly every other vaccine in use.

"We shouldn't wait to make recommendations about this," she said.

Rasmussen encouraged people who'd had J&J's shot, especially those living in communities with low vaccination rates, to speak with healthcare providers about getting an extra dose.

Dr. Anthony Fauci, President Joe Biden's chief medical adviser, said on Wednesday that the Delta variant accounted for more than 20% of new infections in the US and was the "greatest threat" to the nation's efforts to eradicate COVID-19.

There's no data on how well J&J's vaccine works against the Delta variant. More than 9 million Americans have been given the single-dose vaccine, the CDC said.

Read more: Experts explain why the mRNA tech that revolutionized COVID-19 vaccines could be the answer to incurable diseases, heart attacks, and even snake bites: 'The possibilities are endless'

Jason Gallagher, a clinical professor in infectious diseases at Temple University's School of Pharmacy, told Reuters on Monday that he got J&J's vaccine in a trial in November, and recently had a dose of Pfizer-BioNTech's COVID-19 vaccine.

Gallagher said he was concerned about data that suggested that a single shot of either Pfizer's or AstraZeneca's vaccine was only 33% effective against symptomatic COVID-19 caused by the Delta variant. "So I took the plunge," he said.

Professor Peter Hotez, the dean of the National School of Tropical Medicine at Baylor College of Medicine, tweeted on Thursday that adding a second J&J dose, or an extra shot of Pfizer's or Moderna's vaccine, could provide broader protection against variants, "but we need data and CDC-FDA guidance."

Dr. John Beigel, an associate director for clinical research at the National Institute of Allergy and Infectious Disease, told Reuters on Monday that J&J recipients should wait for more data.

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