PARIS – 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, said a study today.
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 previously had the virus.
Its capacity to evade immune system responses even in vaccinated people suggest that “the virus can potentially circulate in vaccinated individuals – even in areas with high vaccination rates”, said the study’s authors in a press release.
In the small study, researchers at 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 who were previously infected.
In the vaccinated group, 18 received just one dose of CoronaVac – one of the main vaccines in Brazil’s Covid-19 response – while 20 recently received a second jab and a further 15 were vaccinated as part of the Sinovac clinical trial last August.
They found that Gamma was able to escape the antibodies of almost all the participants who received only one dose, as well as those vaccinated last year.
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 must be nine times higher to prevent infection by Gamma than to prevent illness from the previous strain.
The authors said the results mean people who have already survived Covid-19 could be reinfected.
However, they said, since clinical trials suggest that the vaccine is effective in preventing severe illness and death, it could be that the immune response is more complex.
Every dose counts
CoronaVac was approved by the World Health Organisation (WHO) for emergency use last month.
At the time, WHO said it had a 51% efficacy against symptomatic disease and 100% against hospitalisation.
But, results from CoronaVac Phase 3 trials in Turkey – which did not take variants into account – published in the Lancet today showed that two doses have an efficacy of 83.5% in protecting against symptomatic infections.
It also found that the vaccine is 100% effective against hospitalisation.
The study involved 6,559 participants who received the vaccine and 3,470 who were given a placebo.
All are adults aged between 18 and 59 who were given doses 14 days apart.
The authors said the limitations of the trial include the participants being under 60 and low-risk, calling for further research to test efficacy among older adults and under-18s, as well as against new variants.
“The world needs every possible dose of any safe and effective vaccine against SARS-CoV-2.”
Both papers are to be presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases. – AFP, July 9, 2021
