WHO officials meeting in Geneva Thursday said the yellow fever outbreak first identified in Angola in December was "serious" but decided against declaring a global emergency.

Since December, the potentially deadly virus (pictured above) spread by mosquitoes - that also transmit Zika and dengue fever - has killed nearly 300 people in Angola, among 2,267 cases of reported infection.

Doctors without Borders' director of operations Dr. Bart Janssens described the disease's pattern of spread from Angola as "very unusual" and warned that a potential worst-case scenario should not be dismissed.

University of Minnesota infectious diseases expert Michael Osterholm said "Africa is like a gas can waiting for the yellow fever match to hit it."

In Paris, Institut Pasteur entomologist Paul Reiter warned that the situation could spiral into something "globally catastrophic."

Mosquito counts had risen dramatically, but the world's ability to control them was "absolutely zilch," said Reiter.

'Intensive control measures' needed

Emerging from the WHO expert committee meeting in Geneva, the UN agency's emergency chief Bruce Aylward said the Angola-centered outbreak was "serious and of great concern and requires intensified control measures."

It could spread rapidly in urban areas, Aylward said, referring to the outbreak's predominance in Luanda, Angola's capital.

Committee chair Oyewale Tomori said the outbreak did not meet conditions for it being declared an international health emergency.

Assist local populations, urges RC

Also from Geneva, the International Federation of the Red Cross and Red Crescent said vulnerable populations in Africa must be helped to reduce the risk.

Red Cross health director Julie Hall said Red Cross branches in Angola, the Democratic Republic of Congo (DRC) and Uganda were helping communities eliminate mosquito breading grounds.

Queuing for vaccinations in Luanda province, Angola

The existing vaccine is regarded as effective but global stocks are limited.

Pharmaceutical companies have reportedly been urged by the WHO to boost stockpiles of yellow fever vaccines, from currently five million doses to up to 18 million within a few months.

Toxic cases fatal

About 15 percent of victims of the flu-like disease suffer a more toxic phase that can lead to kidney problems and even death.

Previous cases had been confined to tropical parts of Africa and Latin America. Until this year, yellow fever was never known to have jumped to Asia.

Eleven people have tested positive for yellow fever in China after returning from Angola.

ipj/rc (AFP, dpa, AP)