GENEVA (AP) _ Scientists are working to develop a vaccine to stop the deadly Middle East Respiratory Syndrome, also known as MERS.

In late April, the first case of MERS in the United States was found here in Indiana. The patient, who flew back from Saudi Arabia, caused a breif panic as he was being tested at the Community Hospital in Munster.

About 40 percent of people who became infected have died. Scientists are still trying to understand the virus and why it spreads.

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. “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.

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.

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