A Brazilian man received the Sinovac COVID-19 vaccine in August 2020 as part of his efficacy trial.
SILVIO AVILA / AFP via Getty Images
By Jon Cohen, Sofia Moutinho
Science‘s COVID-19 reports are supported by the Pulitzer Center and the Heising-Simons Foundation.
In the third of a series of conflicting advertisements about a Chinese-made COVID-19 candidate vaccine, Brazilian researchers reported today that the results of their effectiveness trial were less impressive than they claimed last week. When analyzed by stricter criteria than those used previously, the vaccine’s effectiveness against all forms of COVID-19, including mild cases, dropped from about 78% to 50%.
The vaccine still seemed to give almost 100% protection against illnesses serious enough to require hospitalization, although the study has accumulated very few of these cases for this result to reach statistical significance. Commenting at today’s press conference, microbiologist Natália Pasternak Taschner, president of the Question of Science Institute, a Brazilian non-profit organization that aims to support public policies based on scientific evidence, said it was a “clear and clean study” and she stressed that she wants the vaccine for her and her parents. “It goes without saying that this is the best vaccine in the world,” said Pasternak, who was not involved in the trial. “We have to say that this is our vaccine and it is a good vaccine to start the process of controlling the pandemic.”
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The vaccine, produced by Sinovac Biotech in China, contains a chemically inactivated version of SARS-CoV-2, the virus that causes COVID-19. At last week’s press conference that announced the 78% effectiveness, Dimas Tadeu Covas, head of the Butantan Institute – São Paulo state vaccine that is conducting the study with Sinovac – gave some details. (The information was even more schematic at a news conference last month, when the team said only that the effectiveness was over 50%.) But, when pressed by journalists, he replied that that number came from about 220 cases of symptomatic disease. Today, the researchers revealed that the 78% number actually derived from the analysis of COVID-19 cases in which people sought assistance for symptoms and tested positive for the virus – 31 of those cases among the placebo recipients in the study and seven in the vaccinated group .
A more detailed analysis that included study participants who tested positive but had symptoms so mild that they did not seek help, found 167 cases of COVID-19 in the placebo group and 85 in people who received the vaccine, for an estimated effectiveness of 50, 34%. Even considering the statistical uncertainties, this is considerably below the efficacies of more than 90% of three other COVID-19 vaccines already authorized.
But Esper Kallas, a study investigator based on the main campus of the University of São Paulo who spoke at the press conference, notes that, as the definitions of a positive case vary between trials, “there may not be an accurate comparability between studies.” In Brazil’s judgment, the liberal definition of a case “put things on the most difficult test,” said Ricardo Palácios, from Butantan, who served as the study’s clinical director. “It’s like comparing someone who runs a kilometer on paved ground to someone who runs a kilometer with obstacles.”
The guidelines of the World Health Organization and several countries state that a 50% effective COVID-19 vaccine with a lower limit of 30% meets the standards for initial authorization. “It has all the requirements to justify its emergency use,” said Covas. Brazil has one of the most devastating COVID-19 epidemics in the world, and Covas and several other speakers at the news conference said they expected the Sinovac vaccine – which Butantan is now producing – to spread quickly. No vaccine has yet been authorized in Brazil, but regulators are also reviewing data on the effectiveness of a vaccine made by AstraZeneca and the University of Oxford.
Covas said that the report of the new data on the Chinese vaccine shows “our total commitment and transparency in this process”. Previously, Sinovac had asked Butantan not to disclose details of the study so that the company could analyze the data more closely, which led to claims that Brazilian researchers were gagged by the company. Sinovac did not respond to repeated requests for comment from Science.
Kallas notes that the analysis of the current case does not run until November 28, 2020 and “much more” data is now available. The efficacy trials of the Sinovac COVID-19 vaccine are also underway in Turkey and Indonesia and present even more preliminary data. Researchers in Turkey reported on December 24 that they found 91.5% effective with their first 29 cases, and Indonesia reported 65% effective in 25 cases. Indonesia yesterday gave authorization for emergency use of the vaccine.
Epidemiologist Ethel Maciel, from the Federal University of Espírito Santo, said that the choice to disclose vaccine data in different press conferences with vague numbers was harmful. “People started to suspect and were left with many doubts that encouraged the population’s distrust of vaccines”, says Maciel, who works on the federal vaccination plan.
“We need more than ever to reduce moderate and severe cases and, for that, the vaccine is very good”, he says. “But we are going to need a lot of vaccinated people to reduce transmission.”