In addition, questions about the transmission remain unresolved. Vaccinated people with asymptomatic or breakthrough infection may still be able to pass the virus to others, but it is not yet clear how often this happens.
Many experts said that until the science becomes more definitive, or until vaccination rates increase, it is best to err on the side of safety and routine testing. For example, at the Olympics, repeated testing could help protect the wider Japanese population, which has a relatively low vaccination rate, as well as support workers, who may be older and at higher risk.
“It’s the people I’m really most concerned about,” said Dr. Lisa Broseau, a Research consultant at the University of Minnesota’s Center for Infection Disease Research and Policy.
Not only can they contract the virus, putting pressure on the Japanese health care system, but they can also become sources of transmission: “Everyone is at risk, and everyone can potentially be infected,” she said.
All Olympic staff and volunteers have been given the opportunity to be vaccinated, according to the Tokyo 2020 Press Office, although officials did not provide data on how many shots were received.
Instead of testing less frequently, officials could rethink how they respond to positive tests, Dr Binny said. For example, if a person who has been vaccinated and asymptomatic tests positive, he or she should still be isolated – but perhaps close contacts can be monitored, rather than placed in quarantine.
“You’re trying to balance the disruptive nature of what you do when someone has tested positive against any benefit in slowing or stopping the spread of the virus,” Dr Binny said.