What We Know about COVID Vaccine Effectiveness Against the New Variants

As significant new COVID variants emerge, such as those first identified in the United Kingdom and South Africa, experts have raised concerns that these mutated versions of the SARS-CoV-2 virus could have an impact on the effectiveness of vaccines.

While experts say the currently available vaccines should provide at least some protection against the new variants, it is possible that in some cases, they may not function as effectively.

Recent research has shown that the U.K. variant called B.1.1.7, which accounts for a small but fast-growing proportion of cases in the U.S., does not appear to dramatically reduce the protection provided by current COVID-19 vaccines.

But evidence is emerging to suggest that the South African variant in particular—known as B.1.351—may have a significant impact on the effectiveness of some of the currently available vaccines and leading candidates in development.

The results of a clinical trial conducted in South Africa, where the B.1.351 variant has become dominant, showed that the AstraZeneca-University of Oxford vaccine was less effective against this version of the virus, providing limited protection against mild disease.

The authors of the study, which involved around 2,000 participants and has not yet been peer-reviewed, found that the shot had low efficacy against mild and moderate disease—below 25 percent. This level of protection would not meet minimal international standards for authorization.

However, the results of the trial, which was small and only recruited relatively young, healthy people, did not provide evidence to determine whether or not the AstraZeneca-Oxford shot would protect against severe disease and death.

Despite the findings, which led South African authorities to suspend use of the shot, experts are hopeful that it may still induce protection against severe disease—a key capability for any vaccine.

Peter Openshaw, a professor of experimental medicine at Imperial College London, said in a statement: "Vaccines that are effective against the more severe forms of disease may not affect milder forms, so there is optimism that severe disease will still be prevented by vaccines based on the original spike protein despite mutations."

Data from large-scale clinical trials assessing the vaccines being developed by Johnson & Johnson and Novavax have also shown reduced effectiveness against the South African variant.

For example, the Novavax shot was found to be 49 percent effective at preventing symptomatic COVID-19 in South Africa. Meanwhile, the vaccine was found to have an efficacy of around 90 percent in a separate trial conducted in the U.K.—where the B.1.1.7 is dominant.

Similarly, preliminary results from ongoing clinical trials assessing the Johnson & Johnson vaccine found the shot was 72 percent effective at preventing moderate to severe COVID-19 among trial volunteers in the U.S. but only 57 percent among those in South Africa after 28 days.

Despite lower overall efficacy in South Africa, however, the J&J vaccine was 85 percent effective in preventing severe disease across all the regions studied—including South Africa—providing "complete protection against COVID-related hospitalization and death" after 28 days, according to the company.

In light of these findings, Shabir Mahdi from the University of Witwatersrand, the principal investigator of the South African trial AstraZeneca-Oxford vaccine trial, said at a press conference he was "somewhat optimistic" the AstraZeneca-Oxford shot will also protect against severe disease in much the same way.

The AstraZeneca-Oxford vaccine is based on similar technology to the J&J shot, and they both induce a similar antibody response. While this antibody response was reduced against B.1.1.7, vaccines also stimulate other aspects of the immune system and provide additional forms of protection.

The two mRNA vaccines developed by Pfizer-BioNTech and Moderna completed clinical trials before the new variants of concern took hold, so there is not as much high quality data on how the effectiveness of these shots will be affected by new versions of the virus.

But early evidence from lab research suggests that the vaccines will still be effective against the South African variant, albeit slightly less potent perhaps. Because these two vaccines have greater than 90 percent efficacy, experts say they should still provide high levels of protection against new variants.

"There's a lot of headroom in the mRNA vaccines," Linda-Gail Bekker, the deputy director of the Desmond Tutu HIV Centre at the University of Cape Town, told reporters this week, according to STAT. With B.1.351, "even if there is a little bit of ding there, we would still be in a very good space."

In January, Moderna announced the results of lab research suggesting that its vaccine showed reduction in neutralizing antibodies against B.1.351, although the levels generated by the shot remained above those "that are expected to be protective."

Nevertheless, the company said it would develop a booster specifically designed to target B.1.351. Moderna said there was no reduction in neutralization levels against the U.K. variant.

On Monday, a study was published in the journal Nature Medicine, which found that the Pfizer-BioNTech should provide protection against both the South African and U.K. variants, although neutralization of the virus was found to be "slightly lower" in a genetically modified pathogen that researchers designed to imitate the mutations seen in B.1.351.

And earlier this month, researchers from the University of Cambridge found in a lab study that the Pfizer-BioNTech vaccine is likely to be effective against the U.K. variant of SARS-CoV-2, albeit with modest reductions in efficacy.

However, when the E484K mutation—also seen in B.1.351—was added to the U.K. variant, the number of antibodies required to prevent infection significantly increased.

Meanwhile, the AstraZeneca-Oxford vaccine appears to be similarly effective at protecting against symptomatic disease caused by the U.K. variant as it is against the original version of the virus, preliminary results have shown. This is despite the fact that the vaccine appears to provide less protection against the South African variant.


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Health worker administers a COVID-19 vaccine
Health worker administers a COVID-19 vaccine at a drive-through vaccination in St Albans, England, on February 8, 2021. DANIEL LEAL-OLIVAS/AFP via Getty Images

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