Data from 1.2 million members of Israel’s largest health-maintenance organization shows the Pfizer-BioNTech vaccine is 94 percent effective in preventing symptomatic Covid-19 and 92% effective in preventing serious disease in vaccinated people who do get infected.

The study from Clalit Research Institute of Clalit Health Services is thought to be the biggest yet in evaluating how well the vaccine works in the real world.

The survey by the Clalit Health Services HMO compared 600,000 individuals who’d received both doses to 600,000 who were unvaccinated. Of the vaccinated group, 170,000 were over age 60 and 430,000 between 16 and 59.

Epidemiologist Dr. Ran Balicer, founding director of Clalit Research Institute, explained that this is the first time the Pfizer vaccine’s effectiveness in preventing Covid-19 symptoms – not just infections — was studied by comparing vaccinated people with a control group of individuals of similar characteristics.

Balicer and his team analyzed the data with a team from Harvard University.

He tweeted on Sunday, when the study was released: “We need to turn the spotlight now on the young age group, aged 40-60, who have not yet been vaccinated. These are about 500,000 people, 27% of their peers, who do not always perceive themselves as a population at risk, but are now 31% of the [Covid patients on] respirators. One in 30 people at this age who becomes infected will be hospitalized with a serious illness. Go get vaccinated!”