A team of researchers has identified an antibody that is highly protective at low doses against a wide range of viral Covid-19 variants.

Moreover, the antibody attaches to a part of the virus that differs little across the variants, meaning that it is unlikely for resistance to arise at this spot.

The findings, published in the journal Immunity, could be a step toward developing new antibody-based therapies that are less likely to lose their potency as the virus mutates.

"Current antibodies may work against some but not all variants," said researcher Michael S. Diamond from the Washington University in St. Louis in the US.

"The virus will likely continue to evolve over time and space. Having broadly neutralizing, effective antibodies that work individually and can be paired to make new combinations will likely prevent resistance," Diamond added.

To find neutralising antibodies that work against a wide range of variants, the researchers began by immunising mice with a key part of the spike protein known as the receptor-binding domain.

Then, they extracted antibody-producing cells and obtained 43 antibodies from them that recognize the receptor-binding domain.

The researchers screened the 43 antibodies by measuring how well they prevented the original variant of SARS-CoV-2 from infecting cells in a dish.

Nine of the most potent neutralizing antibodies were then tested in mice to see whether they could protect animals infected with the original SARS-CoV-2 from disease. Multiple antibodies passed both tests, with varying degrees of potency.

The researchers selected the two antibodies that were most effective at protecting mice from disease and tested them against a panel of viral variants.

The panel comprised viruses with spike proteins representing all four variants of concern (alpha, beta, gamma and delta), two variants of interest (kappa and iota), and several unnamed variants that are being monitored as potential threats.

One antibody, SARS2-38, easily neutralized all the variants. Moreover, a humanized version of SARS2-38 protected mice against disease caused by two variants -- kappa and a virus containing the spike protein from the beta variant.

The beta variant is notoriously resistant to antibodies, so its inability to resist SARS2-38 is particularly remarkable, the researchers noted.