LONDON (REUTERS) - Existing vaccines may protect against the Brazilian variant of the coronavirus, according to a University of Oxford study which also highlighted how a variant first found in South Africa poses the biggest headache for vaccine makers.

The study was released on a pre-print server, and had not been peer-reviewed.

Coronavirus variants with specific mutations to the spike protein are of concern because scientists worry they will reduce the efficacy of vaccines, as well as immunity gained from prior infection.

The scientists used blood samples from people with antibodies generated by both Covid-19 infection and the Oxford-AstraZeneca and Pfizer-BioNTech vaccines that are being rolled out in Britain.

The data showed a nearly threefold reduction in the level of virus neturalisation by antibodies generated by the vaccines for the P.1 Brazil variant - similar to the reduction seen with the variant first identified in Kent, Britain.

"These data suggest that natural- and vaccine-induced antibodies can still neutralise these variants, but at lower levels," it said.

"Importantly, the P.1 'Brazilian' strain may be less resistant to these antibodies than first feared."

The variant first identified in South Africa triggered a much larger reduction in virus neutralisation, with a ninefold reduction in Oxford-AstraZeneca's vaccine, and a 7.6-fold reduction for Pfizer-BioNTech.

Last month, South Africa put use of AstraZeneca's shot on hold after data showed that it gave minimal protection against mild-to-moderate infection caused by the country's dominant variant.

The authors of the study said that developing vaccines against the South Africa variant, known as B.1.351, should be the "greatest priority for vaccine developers globally".

Professor Andrew Pollard, chief investigator of the Oxford University vaccine trial, said the study provided "new insights that help us be prepared to respond to further challenges to our health from the pandemic virus, if we need to do so".