WHO: Fractional dosing for yellow fever vaccine proposed for emergencies

An approach, known as fractional dosing, is under consideration as a short-term measure in case of yellow fever vaccine shortages for use in emergencies.Experts agreed with the proposal at a meeting convened by WHO to consider potential shortages in yellow fever vaccine due to the outbreak in Angola and Democratic Republic of theCongo.

WHO Strategic Advisory Group of Experts (SAGE) on Immunization reviewed existing evidence that demonstrates that using a fifth of a standard vaccine dose would still provide protection against the disease for at least 12 months and possibly much longer.

This fractional approach is not proposed for routine immunization, as there is not yet enough data available to show that lower doses would confer the life-long protection provided by a vaccination with one full dose.

“Yellow fever outbreaks in Angola, Democratic Republic of the Congo and Uganda are placing unprecedented demands on vaccine supply for emergency vaccination campaigns to control the spread of the disease,” says Jon Abramson, chair of the WHO SAGE on Immunization.

“Right now we have enough vaccines in the global stockpile to cope with the ongoing outbreaks if there are no further extensions. However, given the wide spread of the disease in Angola and the potential for it to get out of control in the city of Kinshasa, in the Democratic Republic of the Congo, WHO and partners are seriously considering the use of this dose-sparing strategy to prevent transmission through large-scale vaccination campaigns.”

In the interim, SAGE found that the available evidence is sufficient to determine that fractional dosing of yellow fever vaccine to one fifth of the standard dose (0.1ml instead of 0.5ml) could be a safe and effective option for mass vaccination campaigns to control urban outbreaks in situations of acute vaccine shortage.

More research is needed to find out whether fractional doses would be effective in young children, who may have a weaker immune response to yellow fever vaccine. Practical issues on administering the reduced doses need further investigation, including obtaining the necessary supply of suitable syringes.

Yellow fever is the only disease specified in the International Health Regulations (IHR) for which countries may require proof of vaccination from travelers as a condition of entry.A yellow fever vaccine given at a fractional dose would not qualify for a yellow fever certificate under the IHR requirements. Travelers will need to obtain the full dose of the vaccine to be eligible for the yellow fever certificate.

The global stockpile, funded by Gavi, the Vaccine Alliance, has 6 million doses for emergency use per year and this has already been depleted twice since February of this year. To date, WHO and partners have sent around 18 million vaccine doses to Angola, Democratic Republic of the Congo and Uganda for emergency use to control the current outbreaks.

In addition to fractional dosing, WHO’s SAGE group is looking at ways to prevent yellow fever outbreaks on a long-term basis by strengthening mass vaccination catch-up campaigns in conjunction with improving routine childhood immunization in countries with yellow fever.

WHO’s response strategy to the ongoing outbreaks requires coordinated work with partners in five areas: surveillance and risk assessment, vaccination, case management, social mobilization and risk communication and vector control.

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