What Does It Mean That the Chinese Vaccine Gives Different Results in Different Countries?

Scientists say that CoronaVac, developed by the Chinese biotechnology company Sinovac, could reduce severe Covid-19 cases, particularly in countries with intense outbreaks.

The release last week of the long-awaited results on the effectiveness of CoronaVac brought disappointment and confusion. However, researchers say that the vaccine could help reduce deaths from this disease.

Brazilian researchers reported that CoronaVac, developed by Sinovac, prevented severe and mild Covid-19 disease by 50.4% in late-stage clinical trials. This is much lower than the 90% effectiveness of other vaccines developed.

The CoronaVac vaccine statistic obtained in Brazil is much lower than in the initial trials of the same vaccine in Turkey and Indonesia, and its effectiveness is below the level initially reported by Brazil. The Butantan Institute in San Paulo announced on 7 January that the vaccine was 78% effective in preventing disease, but this week it emerged that the statistics had been determined using a narrowly defined group of people requiring medical care.

Researchers say that, if the latest results are confirmed, administering the 2-dose vaccine in countries with intense outbreaks, such as Brazil and Turkey, could be immediately beneficial. Hilda Bastian, who works at the Faculty of Medicine at Bond University in Australia, says, “For communities that are truly desperate and have no other option, this vaccine is a wonderful thing.”

In the trials in Brazil, Covid-19 cases were reported in 252 of the 9200 healthcare workers participating in the study. (Of these cases, 85 were vaccinated and 167 were in the placebo group.) None of the vaccinated participants was hospitalized because of severe Covid-19. Paul Offit, a vaccine scientist at the Children's Hospital in Pennsylvania, said that, if the data were confirmed, the vaccine could play a role in preventing disease in every country.

Results and Expert Comments

Prof. Dr. Murat Akova, a researcher in infectious diseases and clinical microbiology at Hacettepe University Faculty of Medicine and the coordinator of the CoronaVac vaccine in Turkey, said, “The data from Brazil are important for Turkey, which plans to begin vaccination under emergency use authorization on 13 January.”

“Brazil's delay in reporting its trial results means that Turkey relied on the early results of its own vaccine effectiveness trials when it agreed to distribute CoronaVac.” he adds. In late November, Turkey reported that the vaccine's effectiveness in preventing symptomatic disease was, based on 29 COVID-19 cases in trials involving 1322 volunteers, 91.2% according to its findings.

Dr. Murat Akova adds, “The results in Brazil were disappointing compared with the leading 2 mRNA vaccines developed by Pfizer-Biontec and Moderna, because those vaccines were more than 90% effective. However, CoronaVac is still valuable for Turkey because it will prevent many cases of severe COVID-19.”

Jarir At Thobari, a vaccine scientist at Gadjah Mada University in Indonesia, says, “Indonesia has also authorized the emergency use of CoronaVac and began using it in its national vaccination program on 13 January. Based on results from vaccine effectiveness trials involving 1600 people, with 25 COVID-19 patients, the vaccine's effectiveness in preventing symptomatic disease was found to be 65.3%.” He also says that, given Indonesia's large population, many people could benefit from the vaccine at 65% effectiveness.

The Different Results Are Not Actually Surprising

Scientists say that these mixed results are not surprising for a vaccine with low effectiveness studied in relatively small numbers of people. Different results were also reported in trials of the COVID-19 vaccine developed by the University of Oxford and the pharmaceutical company AstraZenca. Dr. Hilda Bastian says, “If you have a truly highly effective vaccine, you do not need to work with very many participants to obtain a clear result. But when results are mixed, you need a larger number of participants to understand what is happening.”

2 Important Reasons for the Different Results

1. Including the trials in Brazil, researchers say that CoronaVac's lower effectiveness compared with other vaccines may be due to administering 2 doses 2 weeks apart. This means that participants were not given enough time to reach a high level of immunity.
2. The groups participating in the trials also matter. For example, a study involving only healthcare workers, who are more exposed to the virus, report side effects and are tested, would probably detect milder infections. The situation would be different in studies in Indonesia and Turkey that also included the public in vaccination.

Other Benefits of CoronaVac

Adrian Esterman, a biostatistician at the University of South Australia, says that the launch of CoronaVac, which uses an inactivated form of SARS-CoV-2, could lead to more widespread use of this vaccine in other countries.

Also, while the Pfizer-Biontech vaccine must be stored at -70 degrees, CoronaVac can be kept under refrigerator conditions, which makes its distribution easier. In light of recently reported data, CoronaVac appears safe, with only a few people experiencing mild symptoms such as headaches.

Dr. Hilda Bastian adds that a World Health Organization (WHO) team has reviewed Sinovac's vaccine manufacturing practices in China and that global distribution will accelerate if WHO lists the vaccines for emergency use.

RELATED TOPICS

• Covid-19 Current Statistics for the World and Turkey
• Breaking News and Scientific Developments about Coronavirus

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