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Pfizer booster has 95.3% efficacy against COVID-19 relative to two doses

Embargoed until: Publicly released:
Peer-reviewed: This work was reviewed and scrutinised by relevant independent experts.

Randomised controlled trial: Subjects are randomly assigned to a test group, which receives the treatment, or a control group, which commonly receives a placebo. In 'blind' trials, participants do not know which group they are in; in ‘double blind’ trials, the experimenters do not know either. Blinding trials helps removes bias.

People: This is a study based on research using people.

The Pfizer booster has an efficacy of 95.3 per cent relative to the first two doses, according to the company's ongoing Phase 3 trial results. The randomised controlled trial followed 5000 double-dosed people who received the booster, and 5000 who received a placebo, about 10 months after their initial vaccinations. The researchers say among those who hadn't previously had COVID-19, six boosted participants tested positive during the trial compared to 123 placebo participants. The trial took place when Delta was the dominant COVID-19 variant.

Journal/conference: New England Journal of Medicine

Link to research (DOI): 10.1056/NEJMoa2200674

Organisation/s: Pfizer, USA

Funder: Funded by BioNTech and Pfizer; C4591031 ClinicalTrials.gov number, NCT04955626.

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