Is mRNA vaccine effective against Omicron variant of COVID-19? Study sheds light
USA: Amid the recent scare of the B.1.1.529 (omicron), the new COVID-19 variant, there is a need to assess the effectiveness of the current COVID-19 vaccines against Omicron. Considering this a team of researchers from South Africa (where the omicron variant was first identified), aimed to investigate the effectiveness of the BNT162b2 mRNA vaccine (Pfizer–BioNTech) against the omicron variant in preventing hospitalization for Covid-19. The study was published in the New England Journal of Medicine as a research letter on December 29, 2021.
For this purpose, the researchers estimated the vaccine effectiveness of two doses of the BNT162b2 vaccine (i.e., full vaccination) against hospitalization for Covid-19 caused by the omicron variant using data from Discovery Health, a South African managed care organization.
They compared the vaccine effectiveness against Covid-19 hospitalization associated with the omicron variant among fully vaccinated members, during the period from November 15 to December 7 in South Africa. In which, the researchers dubbed a proxy for dominance of the omicron variant (omicron proxy period), against estimates of vaccine effectiveness between September 1 and October 30, when the delta variant was dominant (comparator period).
In total, the researchers analyzed a total of 133,437 PCR test results that had been obtained during the comparator period, of which 28.6% were obtained at least 14 days after the patient had received the second dose of vaccine. They analyzed 78,173 PCR test results for the proxy omicron period, out of which 32,325 (41.4%) had been obtained at least 14 days after the second dose.
Key findings include:
- The overall test positivity was 6.4% during the comparator period and 24.4% during the proxy omicron period, whereas the Covid-19 admission rate was 10.8% and 2.2%, respectively, as a percentage of positive PCR test results.
- Patients with positive cases were younger during the proxy omicron period than during the comparator period.
- During the proxy omicron period, a vaccine effectiveness of 70% (95% confidence interval was found, a finding that was supported by the results of all sensitivity tests. This measure of vaccine effectiveness was significantly different from that during the comparator period, when the rate was 93% against hospitalization for Covid-19.
To conclude, during the proxy omicron period, the effectiveness of the Pfizer–BioNTech vaccine (albeit at a reduced level) was maintained against hospital admission for Covid-19 that was presumed to have been caused by the omicron variant versus the rate associated with the delta variant earlier in the year. This reduction in vaccine effectiveness may be mitigated by the addition of a booster dose of vaccine, the authors suggest.
Reference:
The study titled, "Effectiveness of BNT162b2 Vaccine against Omicron Variant in South Africa," is published in the New England Journal of Medicine.
DOI: 10.1056/NEJMc2119270
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