“Are the current coronavirus disease 2019 (COVID-19) vaccines effective against Omicron?” is one of the major questions that have surfaced since the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant emerged.
Study: Third BNT162b2 vaccination neutralization of SARS-CoV-2 Omicron infection. Image Credit: Irina Shatilova/Shutterstock
Researchers at the Ministry of Health and Sheba Medical Center, Israel have conducted a small-scale study on healthcare workers to find the answer. The team observed that three doses of the BNT162b2 (Pfizer-BioNTech) mRNA vaccine are required to mount an effective antibody response against the Omicron variant. Moreover, the antibody response observed is four-fold less than that mounted against the Delta variant.
A pre-print version of the study has been published on the medRxiv* server, while the article undergoes peer review.
The emergence of the newest SARS-CoV-2 variant B.1.1.529, named Omicron by the World Health Organization (WHO), has flamed serious concerns among the public health authorities all across the globe. WHO has stated that Omicron has a growth advantage over the delta variant, as it is spreading at a much faster rate even in countries where delta prevalence is high.
While research is being rushed to assess the transmission and virulence potential of Omicron, additional studies are trying to ascertain the efficacy of COVID-19 vaccines against this variant. One such study to test the Omicron neutralization capacity of BNT162b2 mRNA vaccine, which was initially reported to have 95% efficacy against wild-type (WT) SARS-CoV-2, has recently been carried out by the Israeli team.
About the study
Neutralization efficacies of Omicron infected cells by the sera of two-dose BNT162b2 vaccinated and three-dose vaccinated healthcare workers were compared.
For the experiment, the team collected 20 serum samples from two groups of individuals: 5-6 months after the second vaccine dose from one group; one month after the third vaccine dose from the second group.
The serum antibodies were tested in vitro against the WT, Beta, Delta, and Omicron isolates by micro-neutralization assay.
Five to six months post second vaccine dose (group 1), the Geometric Mean Titers (GMT) of antibodies were 16.56, 1.27, 8, and 1.11 against WT, Beta, Delta, and Omicron variants, respectively. In group 2, GMTs of 891.4, 152.2, 430.5, and 107.6 were observed for WT, Beta, Delta, and Omicron variants, respectively, one month after the third dose.
BNT162b2 neutralization efficacy was greatly reduced 5-6 months after the second dose against all variants of concern (VOC) compared to WT SARS-CoV-2. Moreover, the vaccine demonstrated almost no antibody/humoral response against the Omicron variant at this time.
Interestingly, the neutralization efficiency against the beta and Omicron variants was alike, both after the second and the third vaccine dose.
Notably, the third BNT162b2 vaccine dose efficiently neutralized Omicron infection (Post-second dose GMT of 1.11 vs. Post-third dose GMT of 107.6)
We demonstrate the importance of a third dose, by showing a 100-fold increase in neutralization efficiency of Omicron following a third dose, with a 4-fold reduced neutralization compared to that against the Delta VOC”, concludes the team.
The team advises generalizing these results with caution as the results are derived from a very small cohort and are based on a single in vitro assay that measures only the antibody response. Nevertheless, the cell-mediated immunity might still be intact and working just fine in the background. Consequently, more studies in larger cohorts are needed to clarify the picture of the entire immune response.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.