Governments from Beijing to Brussels are turning to vaccine passports as a way to safely reopen international travel or provide cover to businesses that require close contact or large gatherings. But given all the uncertainty about the relative efficacy or longevity of competing shots-especially in the face of new variants-the use of vaccination status as a societal get-out-of-jail card remains a leap of faith, medical professionals say. "It may be that the immunity against Covid-19 will differ from vaccine to vaccine, and since we haven't had these vaccines out there for very long, we may not be able to tell for two years," says Birger Forsberg, a professor of international health at the Karolinska Institutet in Stockholm. "You can speculate, you can make theoretical or immunological models, and so on, but as it is said, the proof of the pudding is in the eating."
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