A new dengue vaccine should only be used in people who were previously infected, WHO says

The World Health Organization (WHO) in Geneva, Switzerland, put the brakes on implementation of the world’s first dengue vaccine today when it recommended it only be used in people who have previously been infected with the disease—a move that will shrink the potential market for the vaccine’s producer, Sanofi Pasteur.

Dengue is most dangerous when a person is infected a second (or subsequent) time. Studies have shown that giving the vaccine to people who have never been infected before can leave them vulnerable to a severe reaction if they are subsequently infected. (The vaccine doesn’t confer full protection to the virus.)

The new recommendation, announced today by WHO’s Strategic Advisory Group of Experts (SAGE) on Immunization, is consistent with a warning that Sanofi Pasteur announced in November 2017. But some observers worry that the recommendation could mean the end of the vaccine. No rapid, reliable test for previous dengue infection is available, so the new guidelines mean that the vaccine can’t be widely used; that could lead the company to stop making the vaccine. So far, however, Sanofi Pasteur has expressed confidence in the vaccine.

SAGE is confident that its recommendation will spur development of a diagnostic test, the group’s chairman, Alejandro Cravioto of the National Autonomous University of Mexico in Mexico City, said at a press conference today. In the meantime, he said, “It is for the company to decide how they cope with this.” One of the reasons for the new recommendation is that it’s very important to maintain public confidence in the safety of the vaccine, Cravioto said. The Philippines halted its dengue vaccination campaign in December 2017 and demanded the company reimburse the $70 million the country spent to vaccinate 830,000 children—and that it cover medical expenses for children who develop severe disease.

Cravioto said three new clinical trials of a malaria vaccine called RTS,S, are ready to launch in Ghana, Kenya, and Malawi. Those trials will test the safety and feasibility of giving children four doses of the vaccine, which provides only partial protection against the disease.