August 24, 2017
2 min read

Gaps persist in global yellow fever vaccination coverage

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Notable gaps in vaccination persist in areas at risk of yellow fever virus transmission, with approximately 393.7 million to 472.9 million people still in need of immunization to reach 80% population coverage recommended by WHO, according to recent findings.

“In many yellow fever risk areas, vaccine coverage remains too low to prevent outbreaks,” Freya M. Shearer, DPhil candidate from the Big Data Institute at Li Ka Shing Center for Health Information and Discovery, and colleagues wrote in The Lancet Infectious Diseases. “The course of the Angolan outbreak and international response reiterates the need for a sustained policy of preventive vaccination of at-risk populations to reduce the risk of epidemics.”

Researchers examined global yellow fever vaccination coverage from 1970 through 2016 to calculate how many individuals still require vaccination to reach the population coverage thresholds for outbreak prevention recommended by WHO. They performed an adjusted retrospective analysis using data compiled from WHO reports and health-service-provider registries that included yellow fever vaccination information between May 1, 1939, to Oct. 29, 2016. Shearer and colleagues calculated three population coverage values representing alternative scenarios to account for any uncertainty in how vaccine campaigns were targeted. They then combined that information with demographic data and tracked vaccination coverage through time across countries at risk of yellow fever transmission.

Their analysis revealed significant increases in yellow fever vaccine coverage since 1970. However, prominent gaps still exist in coverage within risk zones in Africa and Latin America. An assessment of yellow fever vaccination coverage by age group in 2016 showed improvement of routine infant vaccination programs in protecting children at the country level, but also revealed gaps in adult populations for most countries. Many individuals (between 393.7 million and 472.9 million) require vaccination in areas at risk of yellow fever virus transmission to reach WHO’s recommended 80% population coverage threshold, the researchers said. This represents between 43% and 52% of the population within the areas at risk, compared with between 66% and 76% of the population who would have needed immunization in 1970.

“The results of this study highlight both important progress and gaps in yellow fever vaccination coverage within risk zones and provide credible estimates of the doses required for supplementary campaigns,” Shearer and colleagues wrote. “The risk of a yellow fever epidemic can be eliminated if effective vector control, vaccination and disease surveillance are enforced and maintained.”

Annelies Wilder-Smith

In a related commentary, Annelies Wilder-Smith, MD, PhD, MIH, professor of infectious diseases at Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, and president of the International Society of Travel Medicine, wrote that this study provides policymakers with the data crucially needed to control yellow fever.

“Absent or erratic control of proof of yellow fever vaccination at entry, falsified vaccine certificates, flawed risk assessments in travel medicine clinics, changing travel patterns and attitudes of travelers and inadequate information by travel medicine providers have led to preventable cases of yellow fever in travelers, which contributes to the spread into new areas,” she wrote. “Although the pre-emptive protection of endemic populations should be the main thrust, efforts should also be enhanced to contain outbreaks rapidly and to stop international spread. The onus is on the world to avoid vaccine shortfalls in the future.” – by Savannah Demko

Disclosures : Shearer reports no relevant financial disclosures. Please see the study for all other authors’ relevant disclosures. Wilder-Smith reports no relevant financial disclosures.