To date, 2,420 cases of yellow fever have been reported in Angola. Despite vaccination campaigns in cities like Luanda, Huambo, and Benguela, 298 people died here due to the disease.
In the current issue of the International Journal of Infectious Diseases, several noted infectious disease specialists from South Africa and Singapore discuss the etiology and epidemiology of yellow fever and offer some insights into the factors that could influence its progression into a full-scale epidemic, reports Science news Online.
The yellow fever vaccine is very effective, and immunization campaigns have been ongoing in Africa. But while over seven million people have been vaccinated for yellow fever, the outbreak in Angola has not been controlled, with new cases popping up almost daily.
The WHO, while concerned over the millions of people still not vaccinated, as well as references to a limited supply of the vaccine, fell short of declaring a global health emergency on May 19, says the New York Times.
“The committee was of the opinion that we have a serious issue on our hands,” said Dr. Oyewale Tomori, a Nigerian yellow fever expert who heads the advisory panel, “but it does not constitute a public health emergency of international concern.”
A difference of opinion over the outbreak’s seriousness
“Unfortunately, this is a misapprehension of the actual situation,” says the infectious disease experts in their journal paper, referring to the situation report issued by WHO after the May 19 meeting. In February of this year, a WHO expert, after visiting the country, reported that the true figures could be actually 10-50 times more, describing an outbreak with thousands of people sickened and hundreds of deaths.
Like diseases in the recent past, such as HIV/AIDS, Ebola, dengue, chikungunya, and Zika, it is far easier with international air travel to have a disease spread quickly to unvaccinated populations. And if yellow fever follows the path of other Aedes mosquito-borne diseases, we are looking at an epidemic waiting to happen.
Lead author Sean Wasserman, with the University of Cape Town, South Africa, warns: “The current scenario of a yellow fever outbreak in Angola, where there is a large Chinese workforce, most of whom are unvaccinated, coupled with high volumes of air travel to an environment conducive to transmission in Asia, is unprecedented in history. These conditions raise the alarming possibility of a YF epidemic, with a case fatality of up to 50 percent, in a region with a susceptible population of two billion people and where there is extremely limited infrastructure to respond effectively.”
As was reported in Digital Journal March 24, when someone infected with yellow fever enters another country, and that country has a mosquito species able to transmit the virus, and the right temperatures, plus the animal reservoir needed to maintain it, then the virus could spread. In other words, if a person with the virus is bitten by the right mosquito, the mosquito could end up being a vector for the disease.
Another concern cited in the paper was the inability to control mosquito populations, as evidenced in Brazil with the Zika virus. With a possible yellow fever epidemic on the horizon and the Zika virus already at epidemic proportions, many countries don’t have the resources to effectively control mosquitoes. The authors say they have little confidence in border controls being effective due to corruption and inefficiencies.
“In the final analysis, vaccination is the only solution, but there are concerns that the world may run out of doses,” according to Dr. Woodall and Dr. Yuill. “There could be a solution. Studies have shown that the vaccine is so potent that one fifth of a dose immunizes just as well – so an existing five-dose vial could protect 25 people. The WHO has the authority to declare the temporary use of the lower dose, which would usefully expand the supply.”
The article, “Yellow fever cases in Asia: primed for an epidemic,” was published in the current issue of the International Journal of Infectious Diseases.
