(CNN) Pfizer-BioNTech's Covid-19 vaccine appears to reduce symptomatic coronavirus infections by more than 90% in the real world, Israeli researchers said Sunday.
The findings, while preliminary, suggest that the vaccine remains remarkably effective in a mass vaccination campaign -- outside the carefully controlled conditions of a clinical trial.
The Clalit Research Institute, part of a large Israeli health system, analyzed data on 1.2 million people, about half of whom had received the Pfizer-BioNTech vaccine. Researchers compared patients who received the vaccine with similar individuals who hadn't.
The rate of symptomatic Covid-19 -- meaning people who were infected with the coronavirus and felt sick -- decreased by 94% among people who received two doses of the vaccine, according to a press release from Clalit. The rate of serious illness decreased by 92%.
Full details of the study weren't immediately available, and the research hasn't yet been peer-reviewed. Still, the findings are consistent with data from Pfizer's own vaccine trial, which found that the vaccine conferred 95% protection against symptomatic Covid-19.
"The affirmation is really important, " says CNN Medical Analyst Dr. Leana Wen, an emergency physician and visiting professor at George Washington University Milken Institute School of Public Health.
"You want to make sure that the study results that we initially were seeing in tens of thousands of people is reflected when, when the population is in the millions."
In the Pfizer trial, researchers randomly assigned patients to receive either the vaccine or a placebo. Then they looked to see how many people got sick in each group, and found that the vaccine sharply reduced illness.
Dr. Eric Topol, executive vice president of Scripps Research Institute, said this is another important aspect reflected in the Israeli study.
"It's highly significant telling us that vaccination, in the real world at scale, achieves remarkable reduction of severe Covid, hospitalizations, and fatalities, fully validating the randomized trial on mRNA vaccines."
Pfizer's study was a randomized controlled trial, the gold standard in clinical research. The Israeli study, on the other hand, was observational, meaning researchers didn't randomly pick who got the vaccine and who didn't.
That can pose problems; people who choose to get vaccinated, for example, may also be more likely to take other steps to protect themselves.
Researchers said they tried to account for those types of effects, however. And observational studies are important because they can offer certain insight into how well vaccines protect people under real-world conditions.
One of those real-world conditions include the presence of new variants, something Wen says is another reason these findings could be important.
"As I understand most of the the strains that are found in Israel at this point are of the B.1.1.7 variant. And so seeing this level of effectiveness, even in a population that has such a high level of that B.1.1.7 variant, is very good news," added Wen, although the researchers have not directly addressed variants in their findings thus far.
Pfizer said it will conduct its own analysis of its vaccine in real-world settings worldwide, including Israel.
"It is our understanding that more than half of the current circulating strains in Israel are the UK variant so our ongoing real-world vaccine effectiveness studies there will reflect the effectiveness against that strain. We will share the analysis from Pfizer when we have the full set of results," the company said in a statement.