Antibodies raised by some COVID-19 vaccines are less effective at neutralising new, circulating variants of the novel coronavirus such as the ones first reported in the UK, South Africa and Brazil, according to a new study.

The research, published in the journal Cell, noted that the neutralising antibodies induced by the Pfizer and Moderna COVID-19 vaccines were less effective against the coronavirus variants first described in Brazil and South Africa.

According to the scientists, including Alejandro Balazs from the Massachusetts General Hospital (MGH) in the US, neutralising antibodies work by binding tightly to the virus and blocking it from entering cells, thus preventing infection.

They said this binding only happens when the antibodies’ and the virus’ shapes are perfectly matched to each other “l(fā)ike a key in a lock.”

If the shape of the virus changes where the antibody attaches to it — in this case, in the spike protein of the novel coronavirus — they said the antibody may no longer be able to recognise and neutralise the virus as well.

In the study, the researchers developed assays for COVID-19, comparing how well the antibodies worked against the original strain versus the new variants.

“When we tested these new strains against vaccine-induced neutralizing antibodies, we found that the three new strains first described in South Africa were 20-40 times more resistant to neutralization,” said Balazs, who is also an assistant professor of Medicine at Harvard Medical School in the US.

According to the scientists, the two strains first described in Brazil and Japan were five to seven times more resistant, compared to the original SARS-CoV-2 virus lineage from Wuhan, China.

“In particular we found that mutations in a specific part of the spike protein called the receptor-binding domain were more likely to help the virus resist the neutralising antibodies,” said Wilfredo Garcia-Beltran, first author of the study from MGH.

The study noted that the three South African variants, which were the most resistant, all shared three mutations in the receptor-binding domain, which may contribute to their high resistance to neutralising antibodies.

However, the scientists said the ability of these variants to resist neutralising antibodies doesn’t mean the vaccines won’t be effective.

“The body has other methods of immune protection besides antibodies. Our findings don’t necessarily mean that vaccines won’t prevent COVID, only that the antibody portion of the immune response may have trouble recognising some of these new variants,” Balazs said.

The researchers added that understanding which mutations are most likely to allow the virus to evade vaccine-derived immunity is essential to develop next-generation vaccines that can provide protection against new variants.

They said this can also help researchers develop more effective preventative methods, such as broadly protective vaccines that work against a wide variety of variants, regardless of which mutations develop.