Booster dose of Covaxin vaccine candidate neutralizes Omicron and Delta variants

In a recent study published on the medRxiv* preprint server, researchers evaluate the neutralization potential of sera samples from subjects boosted with the coronavirus disease 2019 (COVID-19) vaccine Covaxin against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant.

Study: Covaxin (BBV152) Vaccine Neutralizes SARS-CoV-2 Delta and Omicron variants. Image Credit: Golden Shrimp / Shutterstock.com

Background

Covaxin (BBV152) is an inactivated whole virion vaccine that elicits robust antibodies and cell-mediated immune memory responses against SARS-CoV-2. In adults, Covaxin is safe, well-tolerated, and associated with 77.8% and 93.4% efficacy against symptomatic and severe symptomatic SARS-CoV-2 infection, respectively.

Previous studies have demonstrated that sera samples from Covaxin vaccinees efficiently neutralized the SARS-CoV-2 Alpha, Beta, Delta, Zeta, and Kappa variants. However, the recent emergence of the SARS-CoV-2 Omicron variant, with more than 30 mutations in its spike (S) region, was associated with an increase in breakthrough infection rates in individuals vaccinated with the primary vaccination series and booster vaccination.

The lower neutralizing responses of vaccine-induced antibodies against Omicron might be associated with a higher risk of symptomatic SARS-CoV-2 infection, disease severity, and COVID-19-related hospital admission. Taken together, sufficient information regarding the Omicron neutralization potential of the Covaxin booster vaccine is not available yet.

About the study

In the present study, researchers evaluate the neutralizing capacity of sera samples from individuals who received a Covaxin booster after six months of primary vaccination series against the SARS-CoV-2 Omicron variant.

Thirteen sera samples were collected after 28 days of booster administration from an ongoing Phase II clinical trial, which randomized previously vaccinated subjects after six months and individuals who received the Covaxin booster dose on the 215^th day.

The neutralizing capacities of the Covaxin boosted sera samples against the SARS-CoV-2 D614G strain, as well as the Delta and Omicron variants, were evaluated using the live virus focus reduction neutralization test (FRNT). Further, the live virus neutralization assay also assessed the Omicron neutralizing capacity of the messenger ribonucleic acid (mRNA) vaccine boosted sera samples.

Study findings

Sera samples obtained from individuals who received the BBV152 booster vaccination successfully neutralized the SARS-CoV-2 Delta and Omicron variants, as well as the wild-type D614G strain in the live virus FRNT.

The geometric mean titers (GMT) of individuals boosted with Covaxin were 75 for Omicron, 480 for Delta, and 706 for the wild-type SARS-CoV-2 strain. Thus, the SARS-CoV-2 Delta and Omicron variants demonstrated a 1.5- and 9.4-fold GMT reduction compared to the D614G strain.

While 100% of the individuals boosted with Covaxin demonstrated neutralizing activity against the SARS-CoV-2 Delta variant, more than 90% neutralized the Omicron variant.

Moreover, the live virus neutralization assay showed that Covaxin boosted sera samples had similar neutralizing activity against the Omicron variant as the sera samples of individuals who received mRNA booster vaccination.

Neutralization antibody responses against D614G, B.1.617.2 (Delta), and B.1.1.529 (Omicron) SARS-CoV-2 variants post-Covaxin booster dosing.

Conclusions

The study findings demonstrate the presence of robust neutralizing antibody responses against the SARS-CoV-2 Omicron variant following the Covaxin booster vaccination. Further, the sera samples of Covaxin boosted individuals neutralized both the SARS-CoV-2 Delta and Omicron variants. Omicron neutralization was comparable between the Covaxin and mRNA booster vaccinated sera samples.

Overall, the study highlights the significance of booster vaccine campaigns considering the waning neutralizing capacity of the primary vaccination series and the emergence of heavily mutated SARS-CoV-2 variants like Omicron. The current study also provides evidence for Covaxin booster vaccination-associated Omicron neutralization.

However, the present study had some limitations including and small sample size. The important role of T-cell immunity in COVID-19 protection was also not accounted for in this study. Furthermore, the researchers also failed to demonstrate the correlation between the neutralization findings and COVID-19 clinical outcomes.

*Important notice

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.