The British Olympic Association is still trying to convince some athletes to get vaccinated against Covid-19 before next month's Tokyo Olympics, chief executive Andy Anson said.
The BOA said earlier this month it was on track to ensure all athletes and staff were fully vaccinated before the Olympics.
The Tokyo Games, delayed last year because of the Covid-19 pandemic, will begin on July 23.
"We're trying to convince them it's the right thing to do," Anson told the BBC on Friday. "People have got the right to choose, and we have to respect that. But it's not necessarily that helpful."
Japan has largely avoided the kind of explosive Covid-19 outbreaks that have devastated other countries, but its vaccine roll-out was initially slow and the medical system has been pushed to the brink in some places.
Many Japanese people remain sceptical about the possibility of holding even a scaled-down Games safely during the pandemic. Organisers have excluded foreign spectators and limited the number of domestic ones for the event.
Anson said the Athletes' Village in Tokyo will be "probably the toughest environment in sports at this time".
"We are putting in place very strict protocols along with the organisers to make sure, to the fullest extent possible, we follow the rules of isolation, distancing, and just keeping in our own 'semi bubbles,'" he said.
On Wednesday, a second member of Uganda's Olympic delegation, an athlete, tested positive for Covid-19 after arriving in Japan.
It comes after a first member of Uganda's Olympic team tested positive and was denied entry into Japan, in the first detected infection among arriving athletes for the Games that begin in five weeks.