Relying solely on the Chinese-manufactured Sinovac inactive vaccine is not enough to reduce transmission rates of COVID-19. Millions of people in 48 countries around the globe have been vaccinated by the mRNA vaccine.

Results from a new study by researchers at Yale and the Dominican Republic published in the journal Nature Medicine say that vaccinations with the Chinese-manufactured Sinovac inactive vaccine alone are of no help against the widely circulating Omicron variant.

The research is based on an analysis of blood serum from 101 individuals from the Dominican Republic. The analysis showed that Omicron infection produced no neutralizing antibodies among those who received the standard two-shot regimen of the Sinovac vaccine.

However, antibody levels against Omicron rose among individuals who had also received a booster shot of the mRNA vaccine made by Pfizer-BioNTech.

Yet, when scientists compared these samples with blood serum samples stored at Yale, they discovered that even samples from individuals who had received two shots of Sinovac and a booster had antibody levels that were only about the same as those who had received just the two shots of the mRNA vaccines, sans any booster shot.

Also, the researchers found that individuals who had been infected by earlier strains of the SARS-Cov-2 virus saw little immune protection against Omicron.

Complicating global efforts

These findings can complicate global efforts to combat the Omicron strain, which, though less dangerous than the Delta strain, is highly transmissible and is the dominant COVID-19 strain circulating in much of the world.

An additional booster shot — and possibly two — will be needed in areas where the Sinovac shot has been the chief source of vaccination, said the paper’s senior author, Akiko Iwasaki.

“Booster shots are clearly needed in this population because we know that even two doses of mRNA vaccines do not offer sufficient protection against infection with Omicron,” she said.

Omicron has proven particularly problematic to combat because it possesses 36 mutations on the spike proteins on its surface. The virus uses these surface spike proteins to enter cells. The mRNA vaccines available today have been designed to trigger antibody response when the body recognises the spike proteins.

Iwasaki stressed, however, that the human immune system still has other weapons it can use against COVID-19, such as T cells that can attack and kill infected cells and prevent severe disease.

“But we need antibodies to prevent infection and slow transmission of the virus,” she said.

The Chinese-manufactured Sinovac inactive vaccine is used in 48 countries to help reduce transmission rates of COVID-19.

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