The first dose of the Pfizer vaccine is 85 percent effective against coronavirus infection between two and four weeks after vaccination, a study published in the medical journal Lancet said.
That study was conducted on health care workers at a hospital in Israel.
The hospital, on December 19, had launched a major vaccination campaign rated as the fastest in the world.
Israeli studies have found that the Pfizer vaccine is 95 percent effective a week after the second injection, while the Lancet report targeted more than 9,000 medical workers at a Sheba hospital near Tel Aviv.
About 7,000 received the first dose and the rest were not taken.
From the group, 170 were tested with Covid-19 after tests performed only on those who showed symptoms or had been in contact with coronavirus carriers.
Fifty-two of them were found to have not been vaccinated.
Comparing the two groups, Sheba’s study found that the vaccine was 47 percent effective between one and 14 days after vaccination, rising to 85 percent after 15 to 28 days.
However, scientists are still studying whether people can get a full vaccine to pass on the virus to others.
Israel has delivered a bullet of the Pfizer / BioNTech vaccine to 4.23 million residents, or 47 percent of its nine million population, 2.85 million of whom received the full course of two jobs recommended, health ministry statistics say latest shows.
(with comments from groups)