Omicron is a particularly difficult variant to fight because it has 36 mutations on the spike proteins on its surface – which the virus uses to enter cells. Existing mRNA vaccines are designed to trigger an antibody response when spike proteins are recognized.
This is not the case with the Sinovac vaccine (inactivated vaccine) and “vaccinations with Sinovac alone are of no use against the Omicron variant”, simply write the scientists in their press release. Their analysis of the blood sera of a hundred people vaccinated with Sinovac and infected with Omicron, identifies “no” neutralizing antibodies.
None no neutralizing antibodies against Omicron, after 2 doses of Sinovac
Specifically, the team analyzed the blood serum of 101 people from the Dominican Republic who had followed the standard 2-injection schedule of the Sinovac vaccine.
- While antibody levels against Omicron increased among those who also received a booster injection of the Pfizer-BioNTech mRNA vaccine, no neutralizing antibodies were identified in those participants who did not receive this booster.
- Comparison of these samples with blood serum samples stored at Yale, shows that even 2 injections of Sinovac + 1 booster with the Pfizer-BioNTech mRNA vaccine induces antibody levels only similar to those obtained with only 2 injections. mRNA vaccines (and without booster);
- the authors point out that previous studies have shown that after a few months, the 2-dose schedule with an mRNA vaccine – and therefore without a booster – offers only limited protection against Omicron.
- Finally, the study also shows that people previously infected with previous strains of the SARS-Cov-2 virus only developed weak natural immunity against Omicron.
What can we conclude from this? Taken together, these results call, after 2 doses of the Sinovac vaccine to perform a booster or booster, or 3rd dose with an mRNA vaccine. These data will no doubt help to better 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.
“The extra booster – and maybe even 2 injections?– is clearly needed in areas of the world where the Sinovac vaccine has been preferred”, writes the lead author, Dr. Akiko Iwasaki, professor of immunobiology. The author points out, 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 serious disease.
“But we need antibodies to prevent infection and slow the transmission of the virus.”