Sharjah24 - AFP: The Chinese CoronaVac jab, a key tool in Brazil's fight against Covid-19, is less effective against the Gamma variant first detected in the virus-ravaged South American country, a study said Friday.

Researchers found that antibodies generated by the vaccine work less well against the variant than a previous coronavirus strain, while Gamma may also be able to reinfect people who had previously had the virus. 

Gamma's capacity to evade these immune system responses even in immunised people suggest "the virus can potentially circulate in vaccinated individuals -- even in areas with high vaccination rates," the study authors said in a press release. 

In the small study, researchers at the University of Campinas in Brazil exposed both Gamma and a previous strain of the virus to antibodies in blood plasma from 53 vaccinated people and 21 people who had been previously infected with the virus.

In the vaccinated group, 18 people had received just one dose of CoronaVac, one of the main vaccines in Brazil's coronavirus response, while 20 had recently received a second jab and a further 15 had been vaccinated as part of the Sinovac clinical trial in August 2020.  

They found that Gamma was able to escape the antibodies of almost all the participants who had received only one dose, as well as those vaccinated in 2020.  

The antibodies from those more recently vaccinated were effective, but less so than against the previous virus strain. 

The study, published in The Lancet Microbe, also found that antibodies produced by previous infections had to be nine times higher to prevent infection by Gamma than to prevent illness from the previous strain.

The authors said those results mean people who have already survived a case of Covid-19 could be reinfected.

But they said since clinical trials suggest the vaccine is effective in preventing severe illness and death, it could be that the immune response is more complex.