The variant of the new coronavirus identified in SA can resist, or "escape," antibodies that neutralise earlier versions of the virus, scientists have found.

It "exhibits complete escape" from three classes of monoclonal antibodies manufactured for treating Covid-19 patients, and it shows "substantial or complete" resistance to neutralising antibodies in blood donated by Covid-19 survivors, the scientists reported on Tuesday on bioRxiv ahead of peer review.

Similarities between this variant and another variant identified in Brazil suggest the variant identified in the South American country will show similar resistance, they added.

Liam Smeeth of the London School of Hygiene and Tropical Medicine, who was not involved in the study, noted that these were laboratory tests, and it would be unwise to extrapolate the findings to humans at this point.

"The data do raise the possibility that the protection gained from past infection with Covid-19 may be lower for re-infection with the variant found in South Africa," he said.

"The data also suggest that the existing vaccines could be less effective against 501. V2."

He called for large studies among populations where the variant is common. 

The Covid-19 vaccine from Pfizer Inc and BioNTech SE is likely to protect against the more infectious variant of the virus discovered in Britain and now spreading around the world, according to laboratory tests.

Researchers took blood samples from 16 people who had received the vaccine and exposed the blood to a synthetic virus, or pseudovirus, that was engineered to have 10 mutations found in the UK variant.

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The antibodies that had developed in response to the vaccine effectively neutralised the pseudovirus, according to a report posted on Tuesday on bioRxiv ahead of peer review.

"This makes it very unlikely that the variant found in the UK will escape from the protection provided by the vaccine," said Jonathan Stoye, a virus scientist at Britain's Francis Crick Institute who was not involved in the research.

Similar experiments are needed with the more concerning variant first found in South Africa, he suggested. AstraZeneca Plc, Moderna Inc and CureVac NV are also testing whether their respective vaccines will protect against the fast-spreading variants. 

Meanwhile, a new study has found that people who have recovered from Covid-19 can likely mount a fast and effective response to the virus if they encounter it again because their immune system's "B cells" will remember how to make the antibodies needed to fight it.

Researchers tracked 87 Covid-19 survivors for six months and found that while levels of antibodies to the virus may decline over time, the number of memory B cells remains unchanged.

The antibodies produced by these cells are more potent than the patients' original antibodies and may be more resistant to mutations in the spike protein the virus uses to break into cells, they said.

For example, they found, the antibodies could recognize and neutralise at least one of the mutations in the variant of the virus found in South Africa.

This variant has caused concern among health experts.

Even if antibody levels fall, B cells will remember how to make them when necessary, according to study leader Michel Nussenzweig of Rockefeller University, whose findings were reported on Monday in Nature.

If this is true at six months, as in this study, it is safe to assume it is probably still true for longer periods, he added.

Therefore, people who have recovered from Covid-19 "may become infected but the immune system will be prepped to fight off the infection," Nussenzweig said.

Researchers also said the more full an intensive care unit (ICU) is with Covid-19 patients, the higher the mortality rate among those patients.