The U.S. Olympic and Paralympic Committee’s medical chief said he was ‘quite happy with the rate of vaccination.

About 100 U.S. Olympic athletes slated to be in Tokyo for the Games are not vaccinated against COVID-19, according to the U.S. Olympic and Paralympic Committee’s medical chief.

Of the 567 athletes who completed their health histories, 83% responded that they were vaccinated against the coronavirus, medical director Jonathan Finnoff said just hours before Friday’s opening ceremony, according to the Associated Press.

Nearly 49% of the entire U.S. population is fully vaccinated, according to estimates from the Centers for Disease Control and Prevention.

The Olympics did not require athletes to get vaccinated before the Games, which were delayed due to the COVID-19 pandemic. Ahead of the opening ceremony, Tokyo was reporting its highest increase in new cases since January.

Olympics officials estimate that 85% of athletes in the Olympic Village are vaccinated against the coronavirus.

The World Health Organization this week remained optimistic about the Games while warning that they aren’t “zero risks” after some athletes tested positive for the virus.

“The mark of success in the coming fortnight is not zero cases, and I know that some cases have already been detected,” WHO Director-General Tedros Adhanom Ghebreyesus said during an International Olympic Committee meeting. “The mark of success is making sure that any cases are identified, isolated, traced, and cared for as quickly as possible, and onward transmission is interrupted.”