A preliminary report from the Clalit Research Institute compared the infection data of 200 000 people aged 60 and over who were not vaccinated with the infection data of 200 000 people of the same age group who received one vaccine dose and were monitored for at least 11 days from the date of vaccination. On day 14 there was a “significant decrease of about 33% in the rate of positive tests for the coronavirus” among those who had been vaccinated. This decrease remained the same between days 15 and 17. The report has raised concerns, as published results have suggested that the efficacy of the Pfizer vaccine was 52.4% between the first and second dose (spaced 21 days apart), and data assessed by Public Health England indicated it could be as much as 89% protective from day 15 to 21. The Clalit Research Institute stressed, however, that its results included only people aged 60 and over—whereas Pfizer trials also included younger people—and that the findings have not yet been peer reviewed. Additionally, the Clalit study identified those infected according to laboratory tests of those who chose to be tested, while Pfizer’s studies only referred to the appearance of symptomatic disease. https://www.bmj.com/content/372/bmj.n217