Results published in the NEJM confirmed recently-released data  from Israel showing that two doses of Pfizer and BioNTech's mRNA-based vaccine BNT162b2 cut the number of symptomatic COVID-19 infections by 94%, whilst also reducing severe illness by 92%. The study is the first analysis of a national COVID-19 vaccination strategy to be peer-reviewed.
Final results  from Pfizer and BioNTech's Phase III study released in November found that BNT162b2 demonstrated an efficacy rate of 95% in preventing COVID-19 in participants without evidence of prior SARS-CoV-2 infection. "We were surprised because we expected that in the real-world setting, where cold chain is not maintained perfectly and the population is older and sicker, that you will not get as good results as you got in the controlled clinical trials," remarked Ran Balicer, senior author on the latest trial, "but we did, and the vaccine worked as well in the real world."
The observational study looked at data from Clalit Health Services, the largest of four integrated healthcare organisations in Israel, and matched 596,618 people given BNT162b2 between December 20 and February 1 with the same number of unvaccinated controls.
Results showed that in the period from 14 through 20 days after the first dose, the vaccine reduced symptomatic COVID-19 infections by 57%, severe illness by 62% and hospitalisations by 74%, while the estimated effectiveness in preventing death from COVID-19 was 72%. At seven or more days after the second dose, the new data show that in addition to cutting symptomatic infection rates and the incidence of severe illness by over 90%, hospitalisations were reduced by 87%.
Balicer noted that researchers also found "the vaccine to be as effective in very different subgroups, in the young and in the old, in those with no co-morbidities and in those with few co-morbidities." Specifically, among people ≥ 70 years old, the rate of symptomatic illness was reduced by 44% in the period from 14 to 20 days after the first dose, jumping to 98% at seven or more days after the second. Individuals with one or two co-existing conditions saw similarly high efficacy, as did those who have three or more, with BNT162b2 reducing symptomatic illness in these two groups by 95% and 89%, respectively, at least a week after the second dose.
Further, findings from the study suggested that BNT162b2 is effective against the B.1.1.7 strain of SARS-CoV-2, which was first identified in the UK, as up to 80% of isolates in Israel consisted of this variant in the days before data extraction. The researchers said that "although we cannot provide a specific effectiveness estimate for the B.1.1.7 variant, the plateau observed during the later periods in the cumulative incidence curve for vaccinated persons suggests that the BNT162b2 vaccine is also effective for this variant." The authors noted that the B.1.351 variant, first detected in South Africa, was estimated to be rare in Israel at the time of data extraction.
Separately, Pfizer and BioNTech announced  that they have started to evaluate what effect a third dose of BNT162b2 will have on immunity against COVID-19 caused by the circulating and potential newly emerging SARS-CoV-2 variants.