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People who have had covid-19 don’t need three vaccine shots

The CDC’s vaccination guidance should acknowledge that past infection provides significant protection against the coronavirus

A person receives a third dose of a coronavirus vaccine at a pharmacy in Livonia, Mich., on Aug. 17. (Emily Elconin/Bloomberg News)

Omicron’s spread is slowing in the United States, but more than 200,000 people a day are still getting infected by the coronavirus. Two factors help to shape both the likelihood of infection and the severity of the disease: whether someone has been vaccinated, and whether they have been previously infected.

Public policy, however, has largely neglected the second factor. The Centers for Disease Control and Prevention, for example, recommends a three-shot regimen for all Americans 12 and older, regardless of whether they have had a previous infection. But requiring people who have been infected to get three shots is overkill at best — a waste of valuable doses — and an unnecessary risk at worst (given that vaccines have side effects, albeit rare ones).

Many companies now demand that their workers show proof that they’ve had two shots and a booster (or one shot of the Johnson & Johnson vaccine plus a booster) — regardless of previous infection status. Allowing workers to submit documentation of a previous infection, plus one additional shot, would not only align mandates with the best research; it might also reduce resistance to vaccination. After all, it’s easier to persuade people to get one shot than three.

The research has long suggested that even unvaccinated people who become infected acquire substantial protection against both symptomatic disease and future hospitalization for covid-19. For example, in one major study of over 30 million people in California and New York, posted last month to the CDC’s website, unvaccinated people with a previous infection — as of the week beginning Oct. 3 — were 29 times (California) and 14.7 times (New York) less likely to be infected than an unvaccinated person with no previous infection. Hospitalization rates showed a similar pattern.

In another study — of Israeli citizens, August to September — previous infection conferred greater protection against future infection than did vaccination alone, and this protection was further increased by a single vaccine dose. Recent findings from Qatar affirm that previous infection also gives high protection, about 88 percent, against severe disease caused by the omicron variant.

In fact, the research shows that “hybrid immunity,” meaning immunity achieved by a combination of vaccination and infection, is stronger than immunity from vaccination alone, regardless of whether infection or vaccination came first.

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While it is too early to tell how well omicron infection will protect against future infection, including possible future variants, it is clear that “cellular immunity” — the arm of the immune system that protects against severe disease and helps generate long-lasting immune protection — “cross reacts” among all of the variants. And emerging data suggest that vaccinated people who become infected with omicron acquire an even broader cellular immunity than vaccinated people who have not been infected with omicron.

The biggest worry about omicron has to do with its increased transmissibility. Could providing three vaccine doses to people with previous infection cut down on viral spread? There is no reason to think so, based on current research. In any case, we already know that vaccination alone can’t reduce transmission without concomitant measures such as testing, social distancing, quarantining after exposures and the diligent use of high-quality masks.

Given what we understand about the immunity caused by infection, policies that rigidly require three vaccine doses — policies promulgated by a growing number of businesses, health-care systems and universities — simply don’t make sense. In some cases, people are losing their jobs because they believe — reasonably, it turns out — that, having been infected, they are well-protected against the coronavirus and are no more likely to transmit it than their vaccinated and boosted peers; they prefer not to receive an unnecessary dose of a medical product. Mandatory three-shot policies are particularly problematic in the university setting, given that young men are at the greatest risk for the vaccine side effect myocarditis.

Booster mandates can also conflict with medical considerations. Many physicians recommend against receiving a dose of vaccine immediately after a coronavirus infection because they reason that it might not work as well. However, booster requirements often do not allow for such subtleties.

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Mandating boosters for people who have been infected with the coronavirus means that unnecessary vaccine doses may be given to many tens of millions of Americans. (All told, there have been more than 77 million covid-19 cases in the United States.) These are wasted doses that could otherwise go to people who really need them, including outside U.S. borders. At least 70 countries continue to have vaccine coverage rates below 40 percent — increasing the likelihood of serious illness in those nations and the emergence of more variants globally.

It would be very simple for public health authorities, including the CDC, to acknowledge that a coronavirus infection is at least as protective as two doses of vaccine. Were that to happen, businesses enforcing vaccine mandates might require no additional shots of people who have had covid-19 (if the goal is “full” vaccination) or one additional shot (if the goal is “up to date” vaccination).

As the number of Americans who have been exposed to the coronavirus swells, such a move could help to reduce covid anxiety and increase trust in our public health agencies. It might even help to persuade some of the 20 percent of the eligible U.S. population who haven’t yet received any vaccine to set aside their hesitancy, since for many of them it would shorten the path to up-to-date vaccination.