China’s Covid vaccine was only 50.4 per cent effective at preventing symptomatic infections in a Brazilian trial, researchers have revealed just days after the scientists claimed it was 78 per cent effective against ‘mild to severe’ cases.
Sinovac Biotech’s results are barely sufficient for the 50 per cent minimum for regulatory approval and well below the rate announced last week.
The news is a major disappointment for Brazil, as the Chinese vaccine is one of two that the federal government had lined up to administer during their deadly Covid surge.
China’s Covid vaccine was only 50.4 per cent effective at preventing symptomatic infections in a Brazilian trial
Many have criticised the Butantan biomedical center for releasing partial data just days ago that generated unrealistic expectations.
The results came from a trial of 13,000 people in Brazil in the most advanced final phase of testing.
Last week, the Brazilian researchers had celebrated results showing 78% efficacy against ‘mild-to-severe’ COVID-19 cases, a rate they later described as ‘clinical efficacy’.
The trial saw 220 people infected of which 160 were in the placebo group and 60 received the vaccine.
But it has now been revealed their results last week did not include data from a group of ‘very mild’ infections from those who had received the vaccine but did not need medical assistance.
With the inclusion of this data, the success rate has now dropped to 50.4 per cent, although the laboratory insists the vaccine is still 78 per cent effective in preventing mild cases that would need treatment.
It is still not clear how the efficacy rate was calculated by the Brazilian officials and a detailed breakdown of the study, showing age groups and side effects, has not been published.
The confusion may add to skepticism in Brazil about the Chinese vaccine, which President Jair Bolsonaro has criticized, questioning its ‘origins.’
Many have criticised the Butantan biomedical center for releasing partial data just days ago that generated unrealistic expectations
‘We have a good vaccine. Not the best vaccine in the world. Not the ideal vaccine,’ said microbiologist Natalia Pasternak, criticizing Butantan’s triumphant tone.
Ricardo Palacios, medical director for clinical research at Butantan, said on Tuesday that the new lower efficacy finding included data on those ‘very mild’ cases.
‘We need better communicators,’ said Gonzalo Vecina Neto, a professor of public health at the University of Sao Paulo and former head of Brazilian health regulator Anvisa.
Piecemeal disclosures about Chinese vaccine trials globally have raised concerns that they are not subject to the same public scrutiny as US and European alternatives.
Palacios and officials in the Sao Paulo state government, which funds Butantan, emphasized the good news that none of the volunteers inoculated with CoronaVac had to be hospitalized with COVID-19 symptoms.
Public health experts said that alone will be a relief for Brazilian hospitals that are buckling under the strain of surging case loads. However, it will take longer to curb the pandemic with a vaccine that allows so many mild cases.
The news is a major disappointment for Brazil, as the Chinese vaccine is one of two that the federal government had lined up to administer
‘It’s a vaccine that will start the process of overcoming the pandemic,’ Pasternak said.
Sinovac and CNBG’s vaccines use an inactivated version of the coronavirus to stimulate the body’s immune response. They can be stored at refrigerator temperature, making them potentially better choices for distribution and use in the developing world
Researchers at Butantan delayed announcement of their results three times, blaming a confidentiality clause in a contract with Sinovac.
In the meantime, Turkish researchers said last month that CoronaVac was 91.25 per cent effective based on an interim analysis. Indonesia gave the vaccine emergency use approval on Monday based on interim data showing it is 65 per cent effective.
Butantan officials said the design of the Brazilian study, focusing on frontline health workers during a severe outbreak in Brazil and including elderly volunteers, made it impossible to compare the results directly with other trials or vaccines.
Still, Covid-19 vaccines in use from Pfizer Inc with partner BioNTech SE and Moderna Inc proved to be about 95 per cent effective in preventing illness in their pivotal late-state trials.
The disappointing CoronaVac data is the latest setback for vaccination efforts in Brazil, where more than 200,000 people have died since the outbreak began – the worst death toll outside the United States.
Brazil’s national immunisation programme currently relies on CoronaVac and the vaccine developed by Oxford University and AstraZeneca Plc – neither of which has received regulatory approval in Brazil.
Anvisa, which has stipulated an efficacy rate of at least 50 per cent for vaccines in the pandemic, has already pressed Butantan for more details of its study, after it filed for emergency use authorization on Friday.
The regulator said it will meet on Sunday to decide on emergency use requests for CoronaVac and the British vaccine.
AstraZeneca failed to deliver active ingredients to Brazil over the weekend, leaving the government scrambling to import finished doses of the vaccine from India to begin inoculations.