New York, Mar 13 (IANS): Neutralizing antibodies induced by the Pfizer and Moderna Covid-19 vaccines were significantly less effective against the SARS-CoV-2 variants first described in Brazil/Japan and South Africa, say researchers.

The team used their experience measuring HIV neutralizing antibodies to create similar assays for Covid-19, comparing how well the antibodies worked against the original strain versus the new variants.

"We were able to leverage the unique high-throughput capacity that was already in place and apply it to SARS-CoV-2," said researcher Alejandro Balazs from Massachusetts General Hospital in the US.

"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, and the two strains first described in Brazil and Japan were five to seven times more resistant, compared to the original SARS-CoV-2 virus," Balazs added.

According to the study, published in the journal Cells, neutralizing antibodies work by binding tightly to the virus and blocking it from entering cells, thus preventing infection.

Like a key in a lock, this binding only happens when the antibody's shape and the virus's shape are perfectly matched to each other, the researcher said.

If the shape of the virus changes where the antibody attaches to it -- in this case, in SARS-CoV-2's spike protein -- then the antibody may no longer be able to recognize and neutralize the virus as well. The virus would then be described as resistant to neutralization, they added.

Currently, all approved Covid-19 vaccines work by teaching the body to produce an immune response, including antibodies, against the SARS-CoV-2 spike protein. While the ability of these variants to resist neutralizing antibodies is concerning, it doesn't mean the vaccines won't be effective.

"The body has other methods of immune protection besides antibodies," said Balazs.

"Our findings don't necessarily mean that vaccines won't prevent Covid, only that the antibody portion of the immune response may have trouble recognizing some of these new variants," Balazs added.