Hartford HealthCare’s Colleen Teevan administers the Pfizer-BioNTech vaccine to a frontline healthcare worker outside of Hartford Hospital. AP Photo/Jessica Hill

Pfizer’s and Moderna’s shots were at least 10 times less effective against variant in a new study.

Researchers tested the vaccines on a variant first found in South Africa, which is now in 20 states.

A mutation on the variant called E484K appeared to be a “major contributor,” the study authors said.

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COVID-19 vaccines from Moderna and Pfizer-BioNTech appear significantly less effective against the coronavirus variant first found in South Africa, a lab study has suggested.

The percentage of protective antibodies that neutralized the variant – called B.1.351, which has been recorded in 20 US states – was 12.4 fold lower for Moderna’s COVID-19 shot than against the original coronavirus, and 10.3 fold lower for Pfizer’s, the study authors said.

This was a bigger drop than in previous lab studies testing the vaccines against manufactured forms of the variant, they said. For this study, the researchers used real forms of the variant taken from people who had caught the virus.

Both the Pfizer and Moderna vaccines have been authorized for emergency use in the US.

B.1.351 was first detected in South Africa in October 2020. It has since spread to 42 countries, including to the US, where it is circulating in at least 20 states, including California and Texas, the Centers for Disease Control and Prevention said. There are 81 reported cases of B.1.351 in the US overall, the CDC said.

The researchers found that the antibody activity from both vaccines was “essentially unchanged” against the variant first found in the UK, B.1.1.7. There are 3,037 reported cases in the US of B.1.1.7, the CDC said, and experts believe it will soon become the dominant strain in the US.

The scientists, from Columbia University, also tested lab-made viruses that had certain mutations. They said that one specific mutation, E484K, appeared to be a “major contributor” to the B.1.351 variant’s ability to evade the antibody response. E484K is not usually present in B.1.1.7, the variant first found in the UK.

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The study has been accepted by science journal Nature but not yet published.

Taking samples from the real world

In the experiment, scientists took 10 blood samples from people who had received two doses of Pfizer’s vaccine, 28 days after their second dose, and 12 samples from those who had received two doses of Moderna’s vaccine, 43 days after their second dose. They then compared how well antibodies in the blood samples “neutralized” the original coronavirus, compared to real-life B.1.1.7 and B.1.351 coronavirus variants.

The sample size was small, and the antibody response is just one aspect of the immune response, so it remains unclear how well the vaccines work against the variant first found in South Africa in real life.

Pfizer has conducted petri-dish tests before that showed a less potent antibody response against a lab-made coronavirus variant that mimicked the variant first found in South Africa. It was not the exact B.1.351 variant. The study, published as correspondence to the New England Journal of Medicine February 17 and updated March 8, suggested the vaccine would work against the variant. It also showed that the antibody response from Pfizer’s shot held up against the variant first found in Brazil, P.1, that has a similar set of mutations to B.1.351.

Moderna ran similar tests and said that its vaccine held up well against the mutations found in B.1.1.7, the variant first found in the UK, but less well against the mutations found in B.1.351, the variant first identified in South Africa. Again, it used lab-made variants.

Both companies said in January that they were developing booster shots specifically to tackle the B.1.351 variant.

Neither of the vaccines has been properly tested against the variant first found in South Africa in the real world.

In Israel, Pfizer’s vaccine has been shown to be highly effective against the B.1.1.7 variant, first found in the UK. About 80% of Israelis with COVID-19 are infected with B.1.1.7.

The COVID-19 vaccine from Johnson & Johnson was less effective in the clinical trials that took place in South Africa.

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