The Biden administration’s push to roll out coronavirus vaccine booster shots this month has largely been shaped by unpublished data from Israel’s vaccination campaign, according to two individuals familiar with the matter.

The Israel data, which is set to be made public as soon as this week, shows that the Pfizer vaccine’s ability to prevent severe disease and hospitalization is waning over time — as is the shot’s protection against mild and moderate disease, the two sources said. The country began administering boosters to people over 60 in July and has now expanded it to people over 30, but it has released relatively little information so far about the effect of the booster campaign.

The Biden administration has long relied on data from Israel, which has one of the highest vaccination rates in the world, to inform its Covid-19 response. Top officials from the White House, the Centers for Disease Control and Prevention and the Food and Drug Administration have analyzed the latest Israeli data for weeks, concluding that the U.S. should begin administering boosters this fall, another senior administration official said.

Although the CDC has published a series of targeted studies that suggest Covid-19 vaccines’ effectiveness against infection is decreasing, particularly in the elderly, the Israeli data is more comprehensive and more alarming, three sources who have reviewed the data told POLITICO on Monday.