Yellow Fever Vaccination: No Booster Needed for Immunity

Joe Barber Jr, PhD

May 20, 2013

A report by the World Health Organization's (WHO's) Strategic Advisory Group of Experts (SAGE) on immunization reveals that a single yellow fever vaccination is sufficient for immunity against the disease.

A summary of the report was published online May 17 in the WHO's Weekly Epidemiological Record.

The SAGE working group reviewed the available data, including 2 systemic reviews, to determine whether booster vaccinations are needed every 10 years to confirm immunity to yellow fever. According to the currently available data, SAGE found that vaccination failures are extremely rare, and no evidence of clustering over time was noted.

"The conventional guidance has been that the yellow fever vaccination has had to be boosted after ten years," said Dr Helen Rees, chair of SAGE, in a WHO news release. "Looking at really very good evidence, it was quite clear to SAGE that in fact a single dose of yellow fever vaccine is effective. This is extremely important for countries where yellow fever is endemic, because it will allow them to reconsider their vaccine scheduling. It is also important for travelers."

The working group recommended that surveillance in endemic countries and clinical studies could help identify populations that would benefit from a booster vaccination. The group also requested that WHO revisit the International Health Regulations provisions concerning the validity of international certifications for yellow fever vaccination.

SAGE mentioned that although persons aged 60 years or older have a higher risk for yellow fever vaccine–associated viscerotropic disease, their overall risk remains relatively low. The group said that the risk–benefit relationship should be assessed for people aged 60 years or older who have not been previously vaccinated and for whom the vaccine is recommended.

Although yellow fever vaccination is not recommended for severely immunocompromised people, the group's data review confirmed that the vaccine was safe for this population, as the vaccine had been included in a mass vaccination program of HIV-infected children in Brazil without safety issues. The group concluded that the vaccine can be offered to all clinically healthy children and that HIV testing is not needed before administering the vaccine.

SAGE recommended additional research on the safety and efficacy of the vaccine, including the persistence of immunity in HIV-infected children and adults.

SAGE also recommended vaccination for pregnant or lactating women who may be traveling to endemic areas in addition to counseling for these women.

Concerning the administration of the yellow fever vaccine with other vaccines, the group noted that a study revealed that the efficacy of the yellow fever vaccine and the rubella and mumps components of the measles, mumps, and rubella vaccine are negatively affected when the vaccines are administered simultaneously, although separating the vaccinations by 30 days eliminated the effect. SAGE recommended additional studies on the administration of the yellow fever vaccine with other vaccines to inform vaccination programs.

"The control strategy for [yellow fever] should include sound epidemiologic surveillance, and delivery of [yellow fever] vaccine through a complementary and optimized combination of routine immunization and mass preventive campaigns," the group writes. SAGE stressed that all at-risk countries should set time-defined objectives for introducing the vaccine and establishing regional plans for controlling the disease.

Wkly Epidemiol Rec. 2013;80:201-216. Full text

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