GENEVA (AP) — Infection rates for the Middle East respiratory syndrome are slowing and scientists are working to stop the dangerous coronavirus from spreading further internationally, a top U.N. health official says.

Most of the 824 confirmed cases of MERS since 2013, including at least 286 deaths, could have been prevented, Dr. Keiji Fukuda, assistant director-general of the World Health Organization, told The Associated Press.

About 40 percent of the people who became infected have died, he said, calling that "a much higher-than-normal fatality rate" for a virus.

"I hope that within the next year or so we really have another significant level of understanding about the virus and how to stop it," said Fukuda, a U.S.-trained physician and former U.N. special adviser on pandemic influenza.

"If we take a look at all of the people that we know got infected (in hospitals), probably the vast majority of those people's infections could have been prevented," he added.

On the other hand, Fukuda says WHO still doesn't understand well enough how people are getting infected in their communities.

Most of the cases have occurred in Saudi Arabia and the virus is thought to be primarily acquired through contact with camels, although he said scientists should do more to find out whether other animals might serve as a reservoir for the virus.

Saudi Arabia has greatly improved its surveillance efforts since a surge of MERS cases in April, Fukuda said, but added more efforts were need ahead of the Muslim pilgrimage season when millions travel to Saudi Arabia.

Pilgrims, particularly those with underlying medical problems, should be made aware of the MERS threat because the Hajj "always has the potential for either bringing in infections or carrying out infections," Fukuda said.

He said researchers are starting to develop a vaccine but that's probably years away from fruition.