Geneva: As of December 12, 2021, seven recent studies have provided evidence of vaccine performance against the Omicron variant: 1 vaccine efficacy/effectiveness (VE) study and 6 neutralization studies. While all studies are preliminary and more data are needed to confirm findings, the World Health Organization stated today that these preliminary laboratory results suggest that the effectiveness of COVID-19 vaccines against infection with the Omicron variant may be reduced.
Two doses of AstraZeneca-Vaxzevria not effective at preventing symptomatic disease due to Omicron.
The first study of real-world VE against the Omicron variant (not yet peer-reviewed) provides preliminary evidence of reduced effectiveness of AstraZeneca-Vaxzevria and Pfizer BioNTech-Comirnaty against symptomatic disease due to Omicron. No data on VE against severe disease was reported. This test-negative case-control study conducted in the United Kingdom found evidence that two doses of AstraZeneca-Vaxzevria was not effective at preventing symptomatic disease due to Omicron, at >15 weeks after the second dose. However, the authors noted that early data for AstraZeneca-Vaxzevria are likely biased due to small numbers and because persons receiving two doses of the vaccine likely reflect an older population and those with more co-morbidities. VE of Pfizer BioNTech-Comirnaty against symptomatic disease was similar to Delta (88.0%, 95% CI: 65.9-95.8%) 2-9 weeks post complete vaccination,
but then fell to 48.5% (24.3-65.0%) at 10-14 weeks post second dose (compared to VE of 77.7%, 95% CI: 76.3-79%, against Delta 10-14 weeks post vaccination). VE against symptomatic disease due to Omicron remained 34-37% from 15-to-25+ weeks post second dose, without evidence of further decrease. Two weeks after receiving a third dose of Pfizer BioNTech-Comirnaty, VE against symptomatic disease due to Omicron increased to 71.4% (41.8-86.0%) among those who had received a primary series of AstraZeneca-Vaxzevria and to 75.5% (95%CI: 56.1 to 86.3%) among those who had received a primary series of Pfizer BioNTech-Comirnaty; in contrast, VE of a third dose against symptomatic disease due to Delta was 93-94% when added to either primary series.
According to WHO, while these results indicate reduced VE of AstraZeneca-Vaxzevria and Pfizer BioNTech-Comirnaty against Omicron, significant bias cannot be ruled out; differences in age and risk among early cases of Omicron among vaccinated versus unvaccinated persons, as well as the predominance of early Omicron cases among travelers and their close contacts, could explain some of the results.
Moreover, due to the small number of Omicron cases detected to date, these early VE estimates are subject to significant uncertainty with wide confidence intervals.
Six studies (not yet peer reviewed) have assessed the ability of blood collected from vaccinated persons to neutralize the Omicron variant.
- One study found an average 41.3-fold reduction in neutralization capacity relative to the ancestral SARS-CoV-2
strain in 12 samples collected 10-39 days after complete vaccination with the Pfizer BioNTech-Comirnaty primary (two-dose) series. - A second study conducted by Pfizer, found a 25.8-fold reduction relative to the ancestral strain among approximately 20 samples collected 3 weeks after completion of the Pfizer BioNTech-Comirnaty primary series. The reduction was only 2.6-fold among samples collected from persons who had received a third dose of Pfizer BioNTech-Comirnaty one month prior to sample collection.
- A third study found that neutralization capacity against Omicron was reduced by 33.5-fold relative to the ancestral strain in persons receiving 2 doses of Pfizer BioNTech-Comirnaty, while the majority of samples from persons receiving two doses of AstraZeneca-Vaxzevria, failed to neutralize the variant.
- A fourth study found that blood collected from individuals who were previously vaccinated with 2 doses of mRNA vaccine 1.3 months prior showed a 127-fold reduction in capacity to neutralize Omicron relative to the ancestral strain; samples collected from persons vaccinated with Janssen-Ad26.COV 2.S 1 month prior failed to neutralize Omicron.
- A fifth study found 20-fold, 11.4- fold, and 10-fold reductions in neutralization capacity compared to Delta for two doses of Moderna-mRNA-1273, fortwo doses of Pfizer BioNTech-Comirnaty, and for a single dose of AstraZeneca-Vaxzevria followed by second dose of Pfizer BioNTech-Comirnaty, respectively, among 14-19 samples collected from persons who had received their second dose 6-7 months prior. Previous studies have found a median 3-fold reduction (IQR 2-4) of these vaccines against Delta relative to the ancestral strain. Adding a third dose of Pfizer BioNTech-Comirnaty to each of three primary vaccination series evaluated, an increase in neutralizing antibodies was observed relative to two doses, however, neutralization capacity against Omicron relative to Delta was still reduced by 23- to 37-fold.
- Finally, a sixth study found that blood collected from persons vaccinated with 2 doses of AstraZeneca-Vaxzevria, 2 doses of Moderna-mRNA-1273, 2 doses of Pfizer BioNTech-Comirnaty, or 1 dose of AstraZeneca-Vaxzevria followed by a second dose of Pfizer BioNTech-Comirnaty had reduced capacity to neutralize Omicron as compared to Alpha, Beta, and Delta variants; a much smaller reduction in neutralization capacity against Omicron was observed for blood collected from persons who had been previously infected and then vaccinated or previously vaccinated and then infected. Of note, these neutralization studies used different assays, sera at variable times after vaccination, and most included sera from a small number of persons.
– global bihari bureau
