Omicron during the holidays

Omicron and Vaccine Efficacy   

    

    Since the initial identification of the Omicron variant in South Africa on Nov. 9 2021, Omicron has been spreading fast across and within countries and is now the dominating variant in multiple regions around the world. In South Africa, 95% of all new positive test samples that have been genetically sequenced are identified as infection by the omicron variant. In the US, US federal health officials announced that Omicron accounted for 73% of new infections last week, a nearly 6 fold increase in only one week. With holiday break right at the corner, is it safe to celebrate with friends and family even if we are vaccinated? Scientists are acting fast to test the effectiveness of vaccines against the Omicron variant. In the recent paper published on medRxiv, a research group in Germany used an in vitro assay to test the neutralization efficacy of vaccine-elicited sera against Omicron.

Background Information

When we receive a COVID-19 vaccination, our body produces T cells and B cells specific against COVID virus and eliminates the virus from our body. One way to measure the protection of a vaccine is to check the level of antibodies for COVID that are produced by B cells. To evaluate the protective capacity, antibody-mediated neutralization efficacy against the Omicron variant was determined using a sera obtained from vaccinated travelers (Pfizer, Moderna or Oxford/AstraZeneca) returning from Zimbabwe. Their antibody levels were compared to that of individuals infected by the Delta variant.

Study Results

Overall, the neutralization efficacy of vaccine-elicited sera against Omicron was severely reduced across all vaccines tested in the study. Neutralization performed with sera from double or triple Pfizer vaccinated individuals (6, 0.5 or 3 months after last vaccination/booster) revealed an 11.4-, 37.0- and 24.5-fold reduction, respectively. Sera from double Moderna-vaccinated and additionally Pfizer-vaccinated individuals (sampled 6 or 0.5 months after last vaccination/booster) showed a 20- and 22.7-fold reduction in the neutralization capacity. Poor neutralization against Delta and no efficacy against Omicron were observed using sera from heterologous AstraZeneca/Pfizer-vaccinated individuals. Additionally, the group receiving a third Pfizer-vaccination showed a significant increase of Neutralizing Ab titers but a 27.1-fold reduction in neutralization against Omicron. Even using sera from double Pfizer-vaccinated and previously SARS-CoV-2-infected individuals, neutralization of Omicron was 32.8-fold reduced.

Implications

This preliminary data indicates that the available vaccines may not be as effective against the omicron variant as with the delta variant. However, data from this study indicates that a third dose of an mRNA based vaccine boosts antibody levels against both omicron and delta variants. Therefore, a good way to stay protected against these COVID-19 variants is to get a booster shot this winter break.

    As with any study, this study has its limitations. The assay used by researchers only tested antibodies produced by B cells but a vaccine generated response includes both T cells and B cells. It's possible that T cells may elicit a different immune response than B cells and that factor needs to be studied further.

More Real World Data

    Despite Omicron’s high transmission rate, studies have found that the variant appears to be less severe. Three separate teams of scientists on two continents have found that Omicron infections more often result in mild illness than earlier variants of the coronavirus. This offers hope that the current surge of cases may not be quite as catastrophic as feared despite skyrocketing caseloads. The results from studies that examined Omicron’s course through populations in South Africa, Scotland and England, all suggest that the variant was less likely to result in hospitalization. Studies based on earlier data from the Gauteng Province in South Africa suggest that Covid-19 cases caused by Omicron tend to be less severe than those associated with earlier variants. In the first four weeks of the Omicron wave, 5.7% of new cases were admitted to the hospital, compared with 15.6% in the Delta wave and 16.2% in the Beta wave. 

    South Africa also delivered more encouraging news last week with official reports suggesting that the wave of COVID-19 infections may have reached its peak as case counts have started falling, and are down by more than 20 percent.

    While it's good news that Omicron cases are beginning to fall in South Africa and the new variant is not as severe, it's important to remember that Omicron is also highly transmissible and experiences reduced efficacy with COVID-19 vaccines. Therefore, my advice to you this holiday season is to get your booster shot, wear a mask, avoid large crowds, but most importantly, enjoy the holiday.

Sources

1. Wilhelm, Alexander, et al. “Reduced Neutralization of SARS-COV-2 Omicron Variant by Vaccine Sera and Monoclonal Antibodies.” MedRxiv, Cold Spring Harbor Laboratory Press, 1 Jan. 2021, https://www.medrxiv.org/content/10.1101/2021.12.07.21267432v3.full-text.