A new, long-term study found no evidence that a Yellow Fever virus vaccination in dengue-endemic areas increased the risk of Severe Dengue Fever.

This is good news since serological interactions between the dengue virus and other flaviviruses, such as Yellow Fever, could drive antibody-dependent enhancements, which is associated with disease severity in dengue infections.

Severe Dengue affects most Asian and Latin American countries and has become a leading cause of hospitalization and death among children and adults in these regions, says the World Health Organization (WHO).

Additionally, both dengue and Yellow Fever virus outbreaks have been reported in similar countries during 2019.

This study evaluated the severity of 11,448 lab-confirmed dengue cases reported in São José do Rio Preto, Brazil.

7,370 patients had been vaccinated for Yellow Fever and they were compared to 4,078 unvaccinated patients.

These researchers regressed dengue severity against Yellow Fever (YF) vaccine status and a number of demographic, clinical, and laboratory variables as controls between 1998 and 2006.

And, they also evaluated the association between YF vaccination status and the clinical and laboratory symptoms of dengue patients.

The study did not find any evidence of increased risk for severe dengue in patients vaccinated against YF (odds ratio = 1.00; 95% confidence interval = 0.87–1.14).

According to the WHO, from July 2018 through March 2019, Brazil recorded a Yellow Fever case-fatality ratio of 23 percent.

In the USA, there are 2 FDA Yellow Fever vaccines available during 2019, YF-Vax and Stamaril.

Recently, the US Food and Drug Administration (FDA) approved the dengue vaccine Dengvaxia for use in the USA for individuals 9 through 16 years of age.

Dengvaxia has already been approved in 19 countries and the European Union.

Sanofi Pasteur’s Dengvaxia is a live, attenuated vaccine that is administered as 3 separate injections, with the initial dose followed by two additional shots given 6 and 12 months later.

Dengvaxia was determined to be approximately 76 percent effective in preventing symptomatic, laboratory-confirmed dengue disease in individuals 9 through 16 years of age who previously had laboratory-confirmed dengue disease.

Dengvaxia is not approved for use in individuals not previously infected by any of the dengue virus 4 serotypes or for whom their immunization information is unknown.

This study was published in Travel Medicine and Infectious Disease on May 8, 2019.

No conflicts of interest were disclosed by these researchers.