Sinovac Covid-19 shot claimed to be more than 50% effective, but data withheld

A 50 per cent efficacy rate is the minimum standard set by US regulators for emergency authorisation of Covid vaccines. PHOTO: REUTERS

BRASILIA (BLOOMBERG) - A Covid-19 vaccine developed by Chinese pharmaceutical firm Sinovac Biotech Ltd was found to be more than 50 per cent effective in a Brazilian clinical trial, though researchers delayed releasing more information at the request of the company.

A 50 per cent efficacy rate is the minimum standard set by US regulators for emergency authorisation of Covid vaccines.

Messenger RNA vaccines from Moderna Inc and Pfizer Inc have produced far better results, reducing symptomatic Covid cases by well over 90 per cent in giant trials.

Chinese vaccine developers have been slow compared with their western peers in releasing efficacy data on their shots.

As millions of healthy people count on transparency in trials before taking a shot, the lack of more specific results from Sinovac's trial risks eroding confidence in vaccines from China.

Hong Kong on Wednesday (Dec 23) said residents will be allowed to choose which shot they want to take among several candidates that will likely include Sinovac's.

The lack of transparency in reporting the Brazil trial results "is totally unacceptable", and wouldn't pass muster in the US, Dr Eric Topol, a clinical trials expert and director of the Scripps Research Translational Institute, said in a phone interview.

"This doesn't have a good look to it at all."

Sinovac didn't respond to calls outside of office hours.

A spokesman said earlier this week that the company could only disclose efficacy data after they are reviewed by Chinese regulators.


The late-stage trial of Sinovac's vaccine in Brazil, involving about 13,000 participants, suggested the shot is "safe and effective", authorities at the Butantan Institute and from the state of Sao Paulo said.

They were asked to not disseminate the information until it was thoroughly reviewed in China as part of a contractual agreement, they said.

"Our goal was for the shot to be more than 50 per cent effective," state Health Secretary Jean Gorinchteyn said at a press conference.

"A vaccine that reaches at least that is already cause for celebration."

The group that received the vaccine in Brazil's trial had no severe cases of Covid-19, and the main side effect reported was mild pain at the injection site, said Professor Dimas Covas, the head of Butantan.

Efficacy is above the threshold needed for a vaccine to be registered by Brazil health regulator Anvisa, which still has to approve the shot, he said.

The trial produced efficacy data that differed from tests carried out in other countries, Dr Gorinchteyn said, without elaborating.

He added that Sinovac's review of the data is slated to take 15 days, but could take less than that, and shouldn't delay the planned Jan 25 start of inoculations with the Sinovac shot.


"Sinovac has several ongoing trials, and it's important it gives the data consistency," Prof Covas said.

"The company can't analyse data from the same vaccine using different criteria, and can't have three different efficacy rates for the same vaccine."

The request by China to delay the efficacy announcement and share the data came at about 9pm local time on Tuesday, researchers said.

Sinovac is also running trials in Indonesia and Turkey.

It is routine for trials of a drug or vaccine conducted in different groups of patients or locations to produce slightly different results, and research groups typically report results of independent trials separately.

Yet while Butantan and state authorities reiterated their optimism for the shot, Dr Topol said the fact that Brazilian authorities would only say that the vaccine is more than 50 per cent effective, but not provide any more detail, suggests that Sinovac efficacy results may not be as good as those achieved by Pfizer and Moderna Inc.


Sinovac is betting on a successful vaccine to inoculate more people around the world and save lives, especially in developing countries like Brazil that will have limited access to the Pfizer and Moderna shots.

Vaccines from Sinovac and other Chinese companies could also help their home country win geopolitical influence and restore an image tarnished by the criticism of its initial response to the virus.

Sinovac's shot is potentially more suited to developing countries because it can be kept at normal refrigerator temperatures.

In contrast, the mRNA vaccines from Pfizer and Moderna require deep-freeze conditions for storage and transportation, making distribution more complicated.

The data delay is also a blow to Sao Paulo Governor Joao Doria's plan to obtain swift approval and begin vaccinating the state of some 45 million people in January.

He's attempting to move quickly while the central government drags its feet on supply agreements and concrete vaccination dates.

Millions of doses of Sinovac's vaccine, called CoronaVac, have already been shipped to Sao Paulo.

The Sinovac vaccine has been at the centre of a political dispute between Mr Doria and President Jair Bolsonaro, who says a vaccine from China can't be trusted.

Mr Bolsonaro, who doesn't plan to take any coronavirus vaccine after being infected earlier this year, has openly bickered with Mr Doria, seen as a contender for presidential elections in 2022.

In addition to Brazil's central government, Butantan is in talks to sell the vaccine to Argentina, Uruguay, Peru, Ecuador and Honduras.

Chile is in talks directly with the Chinese company, according to Prof Covas.

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