Yellow Fever

Yellow Fever

Eliminating Yellow Fever Epidemics (EYE) Strategy: Meeting demand for yellow fever vaccines :: A joint statement by WHO, UNICEF and Gavi
29 January 2018
Vaccination is the most powerful known measure for yellow fever prevention: a single dose can provide life-long immunity at a cost of approximately US$1. Ensuring adequate vaccine supply is available to reach all those at-risk is a constant challenge and the main purpose of the Eliminate Yellow Fever Epidemics (EYE) Strategy partnership, steered by WHO, UNICEF and Gavi, the Vaccine Alliance.

Yellow Fever vaccines are currently manufactured by four WHO-prequalified suppliers. Since 2001, annual yellow fever vaccine production has quadrupled from 20 million to 80 million doses. Output is estimated to increase even further in the coming years. Through the EYE partnership, 1,4 billion yellow fever vaccine doses are expected to be delivered to countries with high yellow fever risk by 2026.

Despite efforts to increase yellow fever vaccine production, there is still a risk that supply will fail to meet demand in Africa if demand reaches the highest projected levels, according to a Gavi study1. In seeking to address this eventuality, the EYE Partnership works closely with manufacturers and yellow fever at-risk countries to plan and ensure vaccines are available in the locations and volume required.

Expanded needs for yellow fever vaccine are a result of a resurgence of yellow fever epidemics in Africa and more recently in Latin America. These resurgences are due to a combination of changing epidemiology and other risk factors including population movement and climate change. These needs are being addressed through routine immunization, preventive mass campaigns, catch-up campaigns (where vaccine coverage is low) and outbreak response (when vaccines need to be supplied rapidly to avoid further spread of the disease).

The International Coordination Group (ICG) coordinates the timely and equitable provision of vaccines during outbreaks. It maintains an emergency stockpile of 6 million doses of yellow fever vaccine funded by Gavi, which is continually replenished.

Demand for yellow fever vaccine has also increased in recent years due to the growing number of countries implementing routine immunization programmes with the support of Gavi. Another important part of the rising demand is the result of efforts, carried out within the framework of the EYE Strategy, to guarantee that yellow fever at-risk countries effectively implement preventive mass vaccination campaigns of all age groups, which frequently require large supply.

With the aim of identifying areas at highest risk, a comprehensive risk analysis and prioritization methodology is being developed to identify areas which should be given priority for preventive mass campaigns. An inaugural meeting on this topic was held on 14-15 December 2017 gathering global experts in WHO, Geneva. Outcomes from the meeting, including risk maps, will support EYE to optimize the allocation of vaccine resources.

Within the framework of the EYE Strategy, detailed plans for vaccine roll-out based on epidemiological risks and priorities are being elaborated. They will support the matching of vaccine supply and demand. This effort is informed by previous work in this area, such as the introduction of the Meningococcal meningitis A vaccine in Africa (MenAfriVac), in 2011, an example of vaccine stock management within the framework of an integrated disease and outbreak control strategy.

WHO, UNICEF, Gavi and all EYE partners are committed to ensuring that every person at-risk of yellow fever is protected. Through combined effort, we are confident that yellow fever epidemics can be eliminated by 2026, and that vaccine supplies can be managed to adequately meet demand.

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Yellow fever: a major threat to public health
Editorial
The Lancet | 3 February 2018
The world’s largest fractional-dose vaccination campaign for yellow fever started on Jan 25 in Brazil, with the support of WHO. The campaign attempts to avoid the urban transmission cycle, not seen in the country since 1942. 33 people have died due to yellow fever between Jan 14 and 23, while the number of confirmed cases in the country has reached more than 130.

Although more cases of yellow fever were recorded in Brazil in 2016–17, the recent outbreak has extended into a much larger area, including highly populated cities, making it more threatening to public health. These large cities are infested by Aedes aegypti, the urban yellow fever vector, which can transmit the disease from person to person. The number of people at risk is also increasing in other tropical regions, such as South America and Africa.

Due to a global shortage of the vaccine, in outbreak emergencies WHO recommends fractional dosing to protect more people by using less antigen in each dose. Whereas studies have shown that a fifth of the standard dose can provide the same immunity as the standard full dose for at least 12 months, it is not clear how long the immunity ultimately lasts.

For routine immunisation, the standard full dose, recommended by WHO since 2013, is thought to confer lifelong protection, although supporting evidence for this view is not strong. Some Brazilian experts believe that a booster vaccine 10 years after the primary vaccination should be administered to guarantee lifetime protection.

As a zoonotic disease, with a reservoir in non-human primates, it is unlikely that yellow fever will be eradicated. However, epidemics can be prevented if populations are protected by routine immunisation and if mass vaccination campaigns are implemented quickly in response to an outbreak. A coalition of partners led by WHO, UNICEF, and Gavi, the Vaccine Alliance, aims to eliminate yellow fever epidemics worldwide by 2026. To achieve this goal, there is an urgent need for research to clarify the duration of protective levels of immunity provided by fractionated and full-dose yellow fever vaccines to support development of effective vaccination programmes.
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