The BNT162b2 vaccine (Pfizer/BioNTech) has previously shown a 95% efficacy against COVID-19. This efficacy has been changing with the surge of new variants and, at present, its effectiveness against the Omicron variant ─ currently the most prevalent ─ remains unknown.
To carry out this study, researchers compared serum samples obtained from participants who had received two doses vs participants who had received three.
Micro-neutralization assays comparing vaccine effectiveness against the wild variant (beta), the Delta and the new variant Omicron were done in two groups of health care workers.
One group had received the complete conventional two-dose scheme (165.6 days from first to second shot) while the other group had also received the booster shot (mean 25 days since application).
Healthcare workers receiving the booster shot showed greater neutralization, both in the wild variant group and the others, compared against patients with two shots.
However, the vaccine had less neutralizing capacity, with both two and three shots, against variants of concern, including Omicron.
This should not discourage us, since the booster shot has multiplied virus neutralizing capacity by 100, even though this figure might be below its efficacy against other variants.
Lastly, third dose durability against Covid-19 remains unknown.
Reference: Ital Nemet et al. N Engl J Med. 2021 Dec 29. Online ahead of print. doi: 10.1056/NEJMc2119358.
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