The United States has based the early direction of its Covid-19 booster strategy on data from other countries, but why? Betsy Ladyzhets highlights the debate and confusion over the U.S. booster policy for FiveThirtyEight.

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The U.S. has relied on data from other countries for its Covid-19 booster strategy

The United States has largely relied on data from other countries, particularly Israel and the United Kingdom, to inform its decisions on Covid-19 booster shots, Ladyzhets writes—even when the information may be "less than ideal" for the purpose.

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For example, scientists from Israel's Ministry of Health and Weizmann Institute presented data from the country's booster shot campaign of the Pfizer-BioNTech vaccine to FDA's vaccine advisory committee last month during a meeting to discuss booster doses of Moderna's and Johnson & Johnson's vaccines.

However, not all FDA's advisors were convinced by Israel's data, which focused on a different vaccine and a smaller, more homogenous population who had received the vaccine earlier than the U.S. population, Ladyzhets writes.

"What they're seeing in Israel is not necessarily what we're seeing here in the U.S.," said Archana Chatterjee, dean of Chicago Medical School and a member of the advisory committee. While Chatterjee said Israel's data is "interesting and compelling," she noted the country differs from the United States on several key characteristics, including a higher vaccination rate and a larger proportion of breakthrough cases leading to hospitalizations before boosters were available. (And for her part, Chatterjee said her votes in favor of booster shots were based on other data.)

How Israel, the U.K. differ from the U.S.

According to Ladyzhets, in addition to Israel, the United States has also turned to the United Kingdom for Covid-19 data because the nation, like Israel, has a universal health care system, which allows it to collect comprehensive health care data in one centralized system.

"During the pandemic, very rapidly, detailed datasets were created that link primary care records, secondary care records, national testing data, and vaccination data," said Jonathan Sterne, a statistician at the University of Bristol.

This standardized Covid-19 data "enabled extraordinary research based on the whole population," Sterne said, since researchers could access anonymized health records for the whole country, including information on a patient's most recent Covid-19 test and their body mass index.

In comparison, the United States does not have a standardized system for health care data, Ladyzhets writes. Instead, all 50 states, along with hundreds of local health departments and thousands of hospitals, have their own different systems.

In addition, integrating records from different sources is difficult because each database uses its own data fields and definitions, Ladyzhets writes, meaning that some information may be recorded differently or even excluded. For example, as of Nov. 7, CDC is missing race and ethnicity data for 35% of Covid-19 cases reported to its database. 

"In the U.S., everything is incredibly fragmented," said Zoë McLaren, a health economist at the University of Maryland. "And so you get a very fragmented view of what's going on in the country." (Ladyzhets, FiveThirtyEight, 11/9)