“Vaccine passports” that exempt vaccinated people from regular COVID-19 testing would allow many infections to be missed, Israeli data suggest.

Researchers analyzed infection rates in citizens returning to Israel through Ben-Gurion airport, for whom PCR tests upon arrival are required regardless of vaccination status.

“Surprisingly,” in August 2021, the rate of positive tests among vaccinated travelers was more than double the rate among the unvaccinated, said Retsef Levi of the MIT Sloan School of Management, coauthor of a report posted on the SSRN server ahead of peer review.

Travelers who had received the second dose of the Pfizer/BioNTech vaccine within the past six months or who had received a booster dose were considered vaccinated. The group considered to be unvaccinated included the never-vaccinated and those whose most recent shot was more than six months prior, given evidence of waning vaccine efficacy by then.

In September, when the Israeli government was recommending booster shots for all adults, the positive-test rate dropped among vaccinated travelers and was about 3.5 times lower with vaccination than without. But by October, the positive-test rate in the vaccinated group, while still lower, had started to climb again, Levi said.

The data suggest that limiting frequent COVID-19 testing to unvaccinated people would “pose potential risks by reinforcing the misrepresentation that vaccinated individuals are protected from infections,” he said.