Thu. Aug 18th, 2022

Several studies suggest that people who have had Covid-19 and are fully vaccinated have strong protection, including against variants, and are unlikely to need boost, even though research is preliminary and data are incomplete, according to researchers who specialize in vaccines and immunology.

More is known about people who had Covid-19 and were then vaccinated, say researchers than those who were vaccinated and had breakthrough infections.

The studies suggest that a Covid-19 exposure effectively acts as a dose of the vaccine, researchers said. Like a vaccine dose, the real infection causes the immune system to generate antibodies, B cells and T cells that can fight the virus in the future.

People who became infected and vaccinated “just won the game,” said Dr. Paul Offit, member of the Food and Drug Administration’s advisory panel on vaccines that support boosters for older adults, but not a widespread campaign this time around. “I would not ask them for a booster dose. I think they just got it ”by exposure to coronavirus.

Strong protection against a combination of a Covid-19 infection and the vaccine does not mean people will never need a booster, researchers said; a vaccination site in Santa Ana, California, in May.


Jae C. Hong / Associated Press

Last week, researchers affiliated with the ZOE Covid Study app, which is for people in the UK to self-report symptoms and test results, said that infection in the real world followed by two doses of the Pfizer-BioNTech shot provided 94% protection up to six months after vaccination compared to 80% protection against vaccination alone or 65% against infection only.

The researchers, who reported the results via a press release, based the results on more than 650,000 Covid-19 test results reported by app users. The results were not peer reviewed or published in a scientific journal.

The strong protection provided by the combination of real infections and vaccinations does not mean that people may not ultimately need a booster, researchers said.

Meanwhile, some people with weakened immune systems or underlying medical conditions may quickly get a boost, the researchers said.

Another factor that people who became infected and vaccinated should weigh before getting a booster is whether the extra dose may increase their potential risk of myocarditis, inflammation of the heart that is rare but most common in younger men. after their second dose of a messenger RNA vaccine, said Peter Hotez, dean of Baylor University’s National School of Tropical Medicine.

Several studies show that the vaccines remain effective in protecting against serious illness and hospitalization, but may lose strength against protecting against infection or milder symptomatic disease.

The Biden administration has pushed for booster shots to strengthen people’s molecular Covid-19 defenses, after some studies showed that protection diminished over time, and the first vaccine series was less effective at protecting against the Delta variant than the original strain.

In the United States, more than 186 million people are fully vaccinated, according to the CDC. The agency stopped tracking breakthrough cases that did not result in hospitalization or death, but a Wall Street Journal analysis in August found that 0.1% of those fully vaccinated at the time had developed cases.

The combination of immunity to a real infection and the protection generated by vaccination is known as hybrid immunity.

So far, data indicate that hybrid immunity provides stronger protection than having been either vaccinated or infected, immunologists and epidemiologists said.

The results suggest that people with hybrid immunity have enough protection without the need for a booster, experts said.

People who have been vaccinated and infected “are probably the last group to really need the booster because they really had three exposures,” said Dr. Akiko Iwasaki, an immunologist at Yale University.

The real-world infection can be particularly additive because it exposes the body to more than the spike protein that vaccines target, she said.

Immunity and the Delta variant

A study published last month by CDC researchers found that unvaccinated people with previous Covid-19 infections are more than twice as likely to become infected again compared to fully vaccinated people who had previous Covid-19 infections. .

Researchers from Rockefeller University in New York said that people who were infected with Covid-19 and later vaccinated with a messenger RNA vaccine saw 20 to 40 times greater immune response than those who were not vaccinated, in a study published in the journal Nature in June.

Researchers from Oregon Health and Science University said that neutralizing antibody levels in humans with hybrid immunity to the Alpha variant were 5.2 times as high as levels in humans who had only been vaccinated, in a study published on the MedRxiv prescription server in April. The team tested other variants and saw similar effects.


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The researchers found that hybrid immunity to infection and vaccination generally provides more immunity than vaccine-induced immunity alone, including to variants. The study has not yet been peer reviewed or published in a scientific journal.

Only individuals who are six months after their second dose received the Pfizer vaccine and fall into several high-risk categories due to age, underlying health conditions, or occupation are currently eligible for boosters. Decisions await Moderna Inc.

and Johnson & Johnson boosters.

Write to Felicia Schwartz at

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