Response to Letter:

The historic and epidemiological perspective of yellow fever (YF) in Kenya highlighted by Monath and colleagues is clearly relevant when deciding policy for its control and prevention in that country. However, the epidemiological descriptors (sylvatic spread, enzootic and silent transmission, potential outbreaks, and threat) are unsatisfactory terms for describing the risk of disease to individuals, and healthcare professionals, prior to vaccination. Current policy appears to be designed to prevent the international spread of YF and is therefore, I would argue, an inappropriate tool for dealing with the personal risk of YF (or the risk of vaccine-associated adverse events) in travelers. The World Health Organization’s (WHO) current recommendations, while recognizing a low risk in urban areas, are unrepresentative of the realistic risk of YF for the majority of the 1.5 million tourists to Kenya.

Policy makers protect populations and prevent disease spread; clinicians make decisions in the best interest of an individual, and they are accountable for any subsequent injury or neglect, including that associated with WHO policy.

An example of where a personal disease threat can be decided without an international policy is immunization against meningococcal meningitis, which is of similar clinical severity to YF. Sensibly, there is no WHO recommendation for all travelers to be immunized, and the decision to vaccinate is left to the health professional and traveler or as an entry requirement.

The current statement by WHO1 that “The risk to unvaccinated individuals who visit countries where there may be yellow fever transmission is far greater than the risk of a vaccine-related adverse event, and it remains important for all travellers at risk to be vaccinated” flies in the face of the YF risk (for tourists) in most of Kenya, bearing in mind the current knowledge of vaccine-associated adverse events. A more balanced approach is proposed by Lindsey and colleagues:2“vaccination should be limited to persons travelling to areas where the risk of yellow fever is expected to exceed the risk of serious adverse events after vaccination.” Monath and the expert panel can contribute to professional practice by providing an estimate of where (and when) in Kenya the YF threat is expected to exceed that of the vaccine risk for the average traveler. The health professional with this knowledge can discuss and decide the balance of risk and benefits of vaccination as is undertaken in most other aspects of travel medicine practice. The current national policy of immunization against YF appears to be a safety net for unknown epidemiological risk or future threat, but with the vaccine’s exceptional toxicity profile, this approach must be questioned.

Health professionals need to be released from the inflexible constraint of WHO policy on YF immunization where international regulations do not apply, so the clinician and traveler can decide the personal hazards between themselves.