The vaccine’s effectiveness can be assessed by the level of antibodies that can neutralize the infection. Studies have shown that vaccines provide less protection against the Omicron strain than the original Wuhan strain:
- Sera from persons vaccinated with two doses of Pfizer-BioNTech or Moderna vaccine have 22-30 times lower neutralizing activity against Omicron.
- Serum neutralizing titers of participants vaccinated with AstraZeneca fell below a detectable threshold.
- In persons vaccinated with CoronaVac, neutralizing antibodies to Omicron were utterly absent.
However, some studies offer hope:
- The administration of three doses of vaccine or a combination of disease and vaccination significantly increases the titer of neutralizing antibodies to Omicron.
- Analysis of sera from individuals vaccinated with Pfizer-BioNTech, Moderna, or Janssen showed a 23-122-fold decrease in neutralizing activity against the Omicron strain. With a combination of infection and vaccination, the titers of neutralizing antibodies decreased only 4-13 times.
Which Vaccine Neutralizes Omicron Better: Sputnik V Or Pfizer-Biontech?
Italian and Russian scientists compared the neutralizing activity of sera against the Omicron strain in COVID-19-free individuals vaccinated with two doses of Sputnik V or Pfizer-BioNTech and in individuals vaccinated with Sputnik V with a history of COVID-19.
Median time after the second dose of vaccine: 91 days (56-122) for Sputnik V and 90 days (14-180) for Pfizer-BioNTech. IgG antibodies were detected in all samples, and IgG levels were comparable between the Sputnik V and Pfizer-BioNTech groups. The levels of neutralizing antibodies to the Wuhan strain of coronavirus were also similar.
The dynamics of IgG in the groups differed. IgG levels after vaccination with Sputnik V were stable. After immunization with Pfizer-BioNTech, the IgG response peaked after 2 weeks, and after 3 and 6 months, the IgG level decreased significantly.
Compared to the Wuhan strain, the level of neutralizing antibodies to the Omicron strain was reduced for vaccines:
- Sputnik V – 8.1 times;
- Pfizer-BioNTech – 21.4 times.
Neutralizing antibodies to the Omicron strain were found in the serum of 74.2% of those vaccinated with Sputnik V and 56.9% of those vaccinated with Pfizer-BioNTech.
Omicron Neutralization Depends on The Time After Receiving The Second Dose of Vaccine
In the sera of persons vaccinated with the second dose of Sputnik V less than 3 months ago, the level of neutralizing antibodies to the Omicron strain decreased by 7.6 times. Neutralizing antibodies to Omicron were detected in 80% of samples. In the sera of persons who received the second dose of Sputnik V 3-6 months ago, the level of neutralizing antibodies decreased by 8.8 times. Neutralizing antibodies were detected in 68.8% of the samples.
Two weeks after administering the 2nd dose of Pfizer-BioNTech, the level of neutralizing antibodies to the Omicron strain decreased by 20.3 times. Neutralizing antibodies to Omicron were detected in 76.5% of samples. At 3 and 6 months after the second dose of Pfizer-BioNTech, the level of neutralizing antibodies decreased by 19 and 25.3 times, respectively. Neutralizing antibodies were found in 58.8% and 35.3% of the samples, respectively.
The combination of COVID-19 infection and vaccination with Sputnik V most effectively protects against Omicron
Russian scientists studied the level of neutralizing antibodies in the blood sera of people vaccinated with Sputnik V and who underwent COVID-19. The study included asymptomatic, mild, or moderate cases of COVID-19 before or after vaccination, as well as patients recovering from COVID-19.
The titers of neutralizing antibodies to the Omicron strain decreased:
- In Sputnik V and asymptomatic form of COVID-19 – by 6.7 times. Neutralizing antibodies to Omicron were found in 87.5% of the samples.
- In Sputnik V and symptomatic form of COVID-19 – by 5 times. Neutralizing antibodies were detected in 100% of the samples.
- In patients recovering from COVID-19 – by 6 times. Neutralizing antibodies were detected in 60.9% of the samples.
Conclusion
Two doses of the vaccine elicit an antibody response that neutralizes the Omicron strain, which may be enough to protect against hospitalization and death with COVID-19. Vaccine studies show that Omicron is much milder in vaccinated people.
However, it is unclear whether the levels of antibodies that have developed in response to vaccination are sufficient to protect against infection with Omicron. According to the UK Health Safety Authority, the use of booster doses of the vaccine can reduce the severity and frequency of cases of COVID-19 caused by the Omicron strain.
Concerning vaccination strategies against novel strains of SARS-CoV-2, studies indicate that heterologous vaccination may improve the immune response compared to homologous. Thus, the Johnson & Johnson vaccine increases the immunogenicity of Pfizer-BioNTech, especially against the Omicron strain.
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