China's Sinovac COVID-19 vaccine was reported to have a general efficacy of less than 60 percent in its late-stage clinical trial in Brazil.

According to Reuters, the news website UOL reported it on Monday, citing two people who saw the results. Sao Paulo's Butantan biomedical center dismissed the report as purely speculative as it prepares to issue a complete set of results on Tuesday.

Director of the Butantan biomedical center, Dimas Covas, said that ongoing analysis had produced a new general efficacy rate in addition to the clinical efficacy announced last week. The Butantan biomedical center is running a late-stage trial of the vaccine in Brazil. 

According to a Bloomberg report, Brazilian researchers said on Thursday that the vaccine was shown to be 78 percent effective against mild cases of COVID-19 and 100 percent effective against severe and moderate infection. 

Related story: Sinovac Vaccine From China Is 78% Effective in Brazil Trial, but Experts Say Details Remain Sketchy

Covas said the trial saw about 220 participants infected with the virus. Around 160 of these participants were placed in the placebo group, and almost 60 received the vaccine.

However, the disclosure did not provide the vaccine trial's complete picture since it was not shown how researchers calculated the efficacy rate. Officials did not also give a detailed breakdown of the study, which includes information about age groups and side effects of the shot.

They also did not specify when they would publish the full documentation of the trials. The Butantan Institute also declined to explain further, saying it had no information beyond what was released in the press conference earlier. 

Sinovac's Data Disclosure

Meanwhile, Beijing-based Sinovac did not immediately respond to inquiries, seeking further information about the ongoing late-stage trials.

Chinese vaccine developers' lack of timely and clear data disclosures have contributed to a lack of trust in their vaccines. An epidemiologist who worked for a long time at the U.S. Centers for Disease Control and Prevention, Denise Garrett, said the data released was not clear nor transparent.

"They presented secondary outcomes on preventing mild cases, serious ones, and hospitalizations, but not the efficacy in preventing disease," Garrett said in a CNBC report.

There was also skepticism about the Chinese vaccine in Brazil due to delayed announcement three times. Nearly half of Brazilians said that they would not take a COVID-19 vaccine developed by China.

Brazil's President Jair Bolsonaro also expressed his hesitation regarding the Sinovac vaccine, mentioning doubts of its origin. Bolsonaro was also known to have exchanged tirades with his political rival João Doria, the Sao Paulo's governor. 

The government of Sao Paulo is currently funding trials and production of the Sinovac vaccine shots. Immunizations have not yet started. Doria repeated that Sao Paulo is set to begin its vaccination program on Jan. 25.

Brazil has the world's second-deadliest COVID-19 outbreak next to the United States. The Latin American country has reported a death toll that passed 200,000 on Thursday.

Brazil is targeting to vaccinate 51 million people or about one-fourth of its total population. The Brazilian government intends to do the vaccination in the first half of 2021.

Other COVID-19 vaccines, such as Pfizer-BioNTech and Moderna, reported having up to 95 percent protection against COVID-19.

Read also: How Long Moderna's COVID-19 Vaccine Gives Protection Against the Virus?