COVID-19 hospitalizations appear to fall sharply after older adults receive the first shot in a two-dose vaccination, and drop by 60% after the second, reports The Times of Israel.

Israel has the world’s fastest COVID-19 vaccination drive so far, allowing a large-scale view of how vaccinations affect coronavirus transmission. Investigators from Maccabi Healthcare Services, Tel Aviv-Jaffa, looked at post-injection data from 50,000 patients aged 60 years and older. They compared COVID-19 hospital admission rates and infections soon after participants received their first dose in December and two days after the second shots were administered in January.

Rates began to plummet at Day 18 after the first shot, and fell by 60% two days after the second (day 23), the study authors reported. What’s more, the results among this senior cohort matched the company’s earlier findings in all-ages study, they said. 

Vaccination may not be the only reason for the drop in cases, said Galia Rahav, M.D., Ph.D., head of infectious diseases at Israel’s largest hospital, Sheba Medical Center. But the findings help at least to partly show what influence vaccination is having on infection rates when cases are high and new strains of the virus are spreading, she told The Times of Israel.

Federal authorities meanwhile are ramping up efforts to track new SARS-CoV-2 variants emerging across the world, according to the Centers for Disease Control and Prevention. The effort is in part to monitor the variants’ effect on COVID-19 vaccines, and efforts are particularly focused on the British strain B.1.1.7, which has arrived stateside and is expected by some experts to become the dominant strain in the United States by March. Officials also are tracking a variant first detected in South Africa that has not yet been detected in the U.S.

Moderna on Monday said lab studies showed its COVID-19 vaccine remains effective against the UK and South Africa variants, though it is less potent against the South Africa strain.