The Brazil trial found the Sinovac vaccine was 50.4 percent effective

The coronavirus vaccine developed by Chinese company Sinovac Biotech is only 50.4 percent effective in preventing COVID-19 symptoms in a Brazilian trial, researchers said on Tuesday, barely enough to gain regulatory approval and far below the rate announced last week.

The latest results represent a major disappointment to Brazil, as the Chinese vaccine is one of two vaccines that the federal government is lining up to start immunization during the second wave of the second most dangerous outbreak of COVID-19 in the world.

Many scientists and observers have criticized the Butantan Institute, a vital medical center, for releasing partial statements just days before that generated unrealistic expectations. Confusion may add to suspicions in Brazil about the Chinese vaccine, which President Jair Bolsonaro has criticized, questioning its “origins”.

“We have a good vaccine. Not the best vaccine in the world,” said microbiologist Natalia Pasternak, criticizing Botantan’s winning rhetoric, “Not the perfect vaccine.”

Last week, Brazilian researchers celebrated results showing 78% efficacy against “mild to severe” COVID-19 cases, a rate they later described as “clinical efficacy”.

But they said nothing at the time about a group of “very mild” infections among those who had received the vaccine but did not require medical help.

Ricardo Palacios, medical director of clinical research in Butantan, said Tuesday that the new, less effective results included data on these “very mild” cases.

“We need better contacts,” said Gonzalo Vicena Neto, a professor of public health at the University of São Paulo and former president of the Brazilian health regulator Anvisa.

The partial disclosure of Chinese vaccine trials worldwide has raised concerns that they have not undergone the same general scrutiny as alternatives developed by US and European manufacturers.

Palacios and officials in the state government of São Paulo, which funds Bhutantan, confirmed that none of the vaccinated volunteers had been hospitalized due to symptoms of COVID-19.

Public health experts said this alone would be a relief to Brazilian hospitals, which are struggling under the pressure of soaring case numbers. However, it will take longer to curb the epidemic with a vaccine that allows for many mild cases.

“It is a vaccine that will start the process of overcoming the epidemic,” Pasternak said.

Delays and disappointments

Researchers in Bhutantan delayed announcing their results three times, and blamed the confidentiality clause in a contract with Senovac.

Meanwhile, Turkish researchers said last month that the vaccine was 91.25 percent effective based on an interim analysis. Indonesia gave approval for the emergency use of the vaccine on Monday based on interim data showing it is 65 percent effective.

Butantan officials said the design of the Brazilian study, which focused on frontline health workers during the severe outbreak in Brazil and involved elderly volunteers, made it impossible to directly compare results with other trials or vaccines.

Workers unload boxes of Chinese COVID-19 vaccine from a truck to a storage building in Banda Aceh. The country gave regulatory approval to vaccinate on Tuesday [Hotli Simanjuntak/EPA]

However, the COVID-19 vaccines used by Pfizer Inc together with its partners BioNTech SE and Moderna Inc have proven to be 95 percent effective at preventing disease in their critical late-stage 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 immunization program is currently based on the Chinese vaccine and the vaccine developed by the University of Oxford and AstraZeneca.

Anvisa, which has stipulated a rate of at least 50 percent efficacy for vaccines in the pandemic, has already pressed Butantan for more details of its study after it applied for permission to use the emergency on Friday.

AstraZeneca failed to deliver the active ingredients to Brazil over the weekend, leaving the government scrambling to import the final doses of the vaccine from India to begin vaccination.

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