LONDON (AP) — The World Health Organization says that the ongoing yellow fever outbreak in Africa is serious but does not warrant being declared an international health emergency.

Since it was first identified in Angola last December, yellow fever has spread to Congo and is believed to have sickened more than 6,300 people and killed about 400, despite millions of doses of vaccine having been sent repeatedly to Angola.

The U.N. health agency convened an emergency committee of experts to consider the outbreak's status on Wednesday and said after its conclusion that the increase of the mosquito-spread hemorrhagic fever appears to have slowed.

The vaccine shortage has now become so acute that officials have begun diluting the vaccine by 80 percent to stretch the supply.