Millions of people around the world have received two injections of Sinovac, the Chinese-made vaccine that is used in 48 countries to help reduce transmission rates of Covid-19.
However, those vaccines alone are not helpful against the Omicron variant, a new study by researchers at Yale University and the Dominican Republic shows. The results are published in the journal
«Nature Medicine» .
An analysis of blood serum from 101 people in the Dominican Republic showed that Omicron infection did not produce neutralizing antibodies among those who received the standard regimen of two injections of the Sinovac vaccine. Antibody levels against Omicron increased among those who also received a booster shot of the mRNA vaccine made by Pfizer-BioNTech.
But when the researchers compared these samples to blood serum samples stored in
Yalefound that even those who had received two injections of Sinovac and a booster had antibody levels that were about the same as those who had received two injections of the mRNA vaccines but no booster. In other studies, the two-injection mRNA regimen without a boost has been shown to offer only limited protection against Omicron.
Additionally, the researchers found that people who had been infected by earlier strains of the SARS-Cov-2 virus had little immune protection against Omicron.
The findings are likely to complicate global efforts to combat the Omicron strain, which has supplanted the more dangerous but less transmissible Delta strain as the most dominant circulating virus in much of the world. An additional booster shot, and possibly two, is clearly needed in areas of the world where the Sinovac shot has been the main source of vaccination, he said. Akiko Iwasaki, professor of immunobiology at Waldemar Von Zedtwitz y main author of the article.
“Booster injections are clearly necessary in this population because we know that even two doses of mRNA vaccines do not offer enough protection against Omicron infection,” Iwasaki said.
Omicron has proven particularly problematic to combat because it has 36 mutations in spike proteins on its surface, which the virus uses to enter cells, the researchers say. Existing mRNA vaccines are designed to trigger an antibody response when spike proteins are recognized.
However, Iwasaki stressed 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 serious illness.