In addition, questions about the transfer remain unresolved. Vaccinated people with asymptomatic or breakthrough infections may still be able to pass the virus on to others, but it is not yet clear how often that happens.
Until that science is more definitive, or until vaccination rates rise, it’s best to side with safety and regular testing, many experts said. At the Olympics, for example, frequent testing could help protect the wider Japanese population, which has relatively low vaccination rates, as well as support staff, who may be older and at higher risk.
“It’s really those people I’m most concerned about,” said Dr. Lisa Brosseau, a research consultant at the Center for Infection Disease Research and Policy at the University of Minnesota.
Not only can they contract the virus, putting pressure on Japan’s health care system, but they can also become a source of transmission: “Everyone is at risk and anyone could potentially be infected,” she said.
According to the Tokyo 2020 press service, all Olympic Games staff and volunteers have been offered the opportunity to get vaccinated, although officials have not provided details on how much the shots received.
Rather than testing less frequently, officials could rethink how they respond to positive tests, said Dr. Binney. For example, if someone has been vaccinated and tests positive asymptomatically, he or she should still be isolated – but perhaps close contacts could simply be monitored rather than quarantined.
“You’re trying to balance the disruptive nature of what you’re doing as someone who has been vaccinated to test positive with any gains in slowing or stopping the spread of the virus,” said Dr. Binney.