Omicron and Delta variants are neutralised by a booster dose of Covaxin vaccine candidate.

Background :  Covaxin (BBV152) is an inactivated whole virion vaccine that produces strong antibodies and cell-mediated immunological memory responses against SARS-CoV-2. Covaxin is safe, well-tolerated, and effective against symptomatic and severe symptomatic SARS-CoV-2 infection in adults, with efficacy rates of 77.8% and 93.4 percent, respectively.

Sera samples from Covaxin vaccinees have been shown to effectively neutralise the SARS-CoV-2 Alpha, Beta, Delta, Zeta, and Kappa variants in previous research. However, the recent appearance of the SARS-CoV-2 Omicron variant, which has over 30 mutations in its spike (S) region, has been linked to an increase in breakthrough infection rates in people who have had both primary and booster vaccinations.

Lower neutralising responses of vaccine-induced anti-Omicron antibodies may be linked to an increased risk of symptomatic SARS-CoV-2 infection, illness severity, and COVID-19-related hospitalisation. Taken together, there isn't enough information about the Covaxin booster vaccine's Omicron neutralisation potential yet.

Concerning the research :  

The neutralising ability of sera samples from people who received a Covaxin booster after a six-month primary vaccination series against the SARS-CoV-2 Omicron variant is tested in this study.

An ongoing Phase II clinical investigation randomised previously vaccinated people after six months and those who received the Covaxin booster dosage on the 215th day, and thirteen sera samples were taken after 28 days of booster therapy

The live virus focus reduction neutralisation test was used to assess the neutralising abilities of Covaxin boosted sera samples against the SARS-CoV-2 D614G strain, as well as the Delta and Omicron variants (FRNT). The Omicron neutralising capacity of the messenger ribonucleic acid (mRNA) vaccine boosted sera samples was also tested using the live virus neutralisation assay.

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Findings of the research :  

In the live virus FRNT, sera samples from people who got the BBV152 booster vaccine successfully neutralised the SARS-CoV-2 Delta and Omicron variants, as well as the wild-type D614G strain.

Individuals boosted with Covaxin had geometric mean titers (GMT) of 75 for Omicron, 480 for Delta, and 706 for the wild-type SARS-CoV-2 strain. In comparison to the D614G strain, the SARS-CoV-2 Delta and Omicron variants showed a 1.5- and 9.4-fold reduction in GMT.

While 100% of those given Covaxin had neutralising efficacy against the SARS-CoV-2 Delta variant, more than 90% had neutralising activity against the Omicron version.

Furthermore, a live virus neutralisation assay revealed that Covaxin-boosted sera samples exhibited equal neutralising activity against the Omicron variant as sera samples from people who had not received the vaccine.

Conclusions : 

Following the Covaxin booster vaccination, the researchers discovered strong neutralising antibody responses against the SARS-CoV-2 Omicron variant. Furthermore, both the SARS-CoV-2 Delta and Omicron variants were neutralised by sera samples from Covaxin-boosted individuals. The neutralisation of Omicron in the Covaxin and mRNA booster vaccinated serum samples was equivalent.

Overall, the study emphasises the importance of booster vaccine campaigns in light of the initial immunisation series' declining neutralising capacity and the introduction of severely altered SARS-CoV-2 variants like Omicron. The current study also shows that Omicron neutralisation is linked to Covaxin booster immunisation.

The current study, however, had numerous drawbacks, including a small sample size. T-cell immunity's crucial involvement in COVID-19 protection was also overlooked in this investigation. Furthermore,