Moderna
Boxes containing Moderna Covid-19 vaccine. (Via Getty)
  • Pfizer-BioNTech and Moderna's Covid-19 shots were at least 10 times less effective against the coronavirus variant first found in South Africa, in a new study.
  • A small lab study – using real versions of the coronavirus – found much lower levels of protective antibodies in both cases.
  • 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 neutralised the variant, called B.1.35, was 12.4 times lower for Moderna's Covid-19 shot than against the original coronavirus, and 10.3 times 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.

B.1.351 was first detected in South Africa in October 2020. It has since spread to at least 42 countries. Data suggests it is the dominant variant in South Africa.

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. 

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.

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 "neutralised" 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. 

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 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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