Millions of people in the U.S. have already received one of the two mRNA vaccines that have proved highly effective against the coronavirus. A one-dose adenovirus-DNA vaccine from Johnson & Johnson is on the verge of authorization. Phase 3 clinical-trial data for five other vaccines deploying different technologies show promising results. Since the peak of the third surge this winter, the number of new cases and hospitalizations has been falling dramatically across the United States. The sharpness of the decline suggests that partial immunity, likely from both natural infection and vaccinations, has started to kick in. In countries with a more rapid mass- vaccination rollout than the U.S., specifically Israel and the United Kingdom, the decline in hospitalizations and cases from vaccines has been even more precipitous.

In response to that good news, skeptics point to several major variants of the virus now circulating in the world: B.1.1.7 (the “U.K. variant”), B.1.351 (the “South Africa variant”), P.1 and P.2 (the “Brazil variants”), B.1.427/B.1.429 (the “California variant”), and B.1.526 (the “New York City variant”). These variants are suspected of being more easily spread from person to person, and conflicting data leave open the possibility that some may be more dangerous to each infected individual.

All of the approved vaccines and major vaccine candidates provide nearly 100 percent protection from severe COVID-19 disease that requires hospitalization or medical treatment, even when tested in countries where variants are circulating. For instance, the Johnson & Johnson single-dose vaccine prevented 100 percent of hospitalizations and deaths across the three sites in which it was tested (the United States, Latin America, and South Africa), despite 95 percent of the viral strains in South Africa at the time being the B.1.351 variant and 69 percent of the strains in Brazil being of the P.2-variant lineage. Protection from mild disease from the variants with the current vaccines is more variable.

Vaccines can work in multiple ways, most familiarly by inducing antibodies that usually provide more short-term protection or protection from mild illness. The COVID-19 vaccines also generate strong T-cell immunity, which not only is more enduring, but works against numerous parts of the virus (including different parts of the spike protein produced by the vaccine), making them more resistant to variants. The astounding protection that the vaccines provide against becoming ill from the coronavirus is likely due to generating a complex T-cell response that makes the disease less severe. In fact, re infection with variants leading to a symptomatic infection is rare following the development of T-cell immunity to an initial infection. Moreover, vaccines have been shown to generate T-cell immune responses directed against multiple regions of the virus—responses that remain potent across variants. Once vaccinated, an individual should be protected against severe disease from any variant.

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