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February 22, 2021

People who have had COVID-19 only may need one vaccine dose, studies suggest

Changing CDC guidelines may free up shots for people who don't have any immunity against the coronavirus, scientists say

Some scientists are urging the U.S. Centers for Disease Control and Prevention to change its COVID-19 vaccine recommendations so that people who have recovered from the coronavirus only receive one shot. 

Several recent studies suggest people who have recovered from an infection only need one dose to boost their antibody protection against the coronavirus. Changing the CDC guidelines could expedite vaccination efforts, researchers say. 

The U.S. vaccination effort has quickened in recent weeks, but supply issues remain an issue. About 64 million vaccine doses have been administered as of 9 a.m. Monday, according to the CDC

The CDC recommends people who have had COVID-19 still get vaccinated because a previous infection does not guarantee future protection. People's immune systems react differently and milder infections might not produce enough antibodies to offer long-term protection, infectious disease experts say. 

Nearly 28 million Americans have tested positive for the coronavirus. If this population only needs one dose for optimum protection, changing the guidelines would free up doses for other people, researchers say. 

Both the Pfizer and Moderna vaccines — the only two currently authorized by the U.S. Food and Drug Administration — currently are administered in a two-dose regimen to anyone who receives them. 

"Everyone should get vaccinated. Not everybody needs two shots," Dr. Viviana Simon, an infectious diseases expert at the Icahn School of Medicine at Mount Sinai, told The Wall Street Journal. "As long as we can't deliver as much vaccine to everybody who wants it, I think it's an important consideration."

The first vaccine dose creates a stronger immune system reaction in people who previously had COVID-19, acting like a booster shot, according to a study conducted by Simon and her colleagues. The study also found the vaccine's side effects were more pronounced among COVID-19 survivors. 

The study, posted on the preprint server medRxiv, included 109 people who had received their first vaccine dose last year. After just one dose, the participants who previously had COVID-19 experienced "very rapid immune responses" that were similar to those of people who received two doses, they wrote. 

Another study found the second dose did not elicit as strong of a reaction in COVID-19 survivors as it did in people who never had been infected by the coronavirus. For them, just one dose was enough to trigger a spike in antibody production. 

"It's a real testament to the strength of the immunologic memory that they get a single dose and have a huge increase," Dr. Mark J. Mulligan, lead author of that study and director of the N.Y.U. Langone Vaccine Center, told The New York Times.

The study, published on medRxiv, analyzed the blood samples of 32 vaccines recipients who had received both doses of the vaccine. 

A third study found that when people with some natural immunity are vaccinated, their blood samples show a 1,000-fold increase in neutralizing antibody titers compared to the blood samples of other vaccine recipients. 

These antibodies were just as effective against the B.1.351 variant from South Africa as they were against the original strain of the virus. But the second dose didn't appear to offer any extra protection to COVID-19 survivors. 

The study, conducted by the University of Washington, also was posted to medRxiv. All three studies still need to be peer-reviewed.

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