WASHINGTON, Aug. 17 (UPI) -- An outbreak of yellow fever in Angola and the Democratic Republic of Congo has grown so significant in recent months that international officials are now moving to vaccinate large numbers of people to stem the spread of the disease.
The World Health Organization is marshaling forces to vaccinate more than 14 million people in the two African countries before the start of the rainy season in September, when the potential for contracting yellow fever may increase, the agency said in a press release on Tuesday.
More than 400 people have died and thousands more have been sickened since the start of the outbreak, which has led officials to ramp up a vaccination campaign much faster than would normally be done.
More than 13 million people in Angola and more than 3 million in the DRC have received the vaccine already, which the WHO said has been crucial to stopping the quick spread of the disease. The next steps are preventive vaccination in areas considered at greater risk, they say.
"Considering that there is a very safe and effective vaccine, this campaign is an essential step to containing the spread of the outbreak, but vigilance will remain crucial in the upcoming months," Axelle Ronsse, emergency coordinator for Doctor's Without Borders, said in a press release.
Doctor's Without Borders is one of 56 global groups that has worked with the WHO to distribute the vaccine in the two countries.
Normally, WHO officials say, just planning a vaccination campaign of this size can take from three to six months. The campaign is expected to require 41,000 health workers and volunteers, more than 500 vehicles and 17.3 million syringes at more than 8,000 vaccination sites.
The outbreak has resulted in global reserves of the yellow fever vaccine being refilled twice since the beginning of the year, and supplies of the vaccine remain limited due to the six-month manufacturing process.
In order to protect as many people as possible before the start of the rainy season in September, the WHO is using factional dosing -- giving people just enough of the vaccine to protect them for at least 12 months, but likely longer -- in order to stretch the existing supply as far as possible.
"Protecting as many people as possible is at the heart of this strategy," William Perea, coordinator for the control of epidemic diseases unit at the WHO, said in a press release. "With a limited supply we need to use these vaccines very carefully."