Dengue vaccine in real-world

Amidst valid concerns from health advocates about the long-term safety and cost-effectiveness of the dengue vaccine Dengvaxia (CYD-TDV), the Department of Health (DOH) rolled out implementation of the dengue vaccination program for school children nine years old and older.

The Strategic Advisory Group of Experts (SAGE), a committee of recognized experts on immunization worldwide, which convenes twice a year to advise the World Health Organization (WHO) on the efficacy and safety of various types of immunization, met last April 12-14 and came out with their preliminary recommendations on April 16.

According to WHO Philippine representative Gundo Weiler during a press briefing at the Department of Health (DOH) on April 18, “the dengue vaccination effort that is currently ongoing in the Philippines is consistent with the recommendations made by the WHO expert group (SAGE). The effort focuses on three regions that have particularly high transmission.”

SAGE stated that Dengvaxia (CYD-TDV), the first approved vaccine for dengue, may be considered for use in geographic settings with high endemicity, as indicated by a seroprevalence of at least 50 percent or greater in the age group targeted for vaccination. The WHO expert group believes that introducing dengue vaccination in high transmission settings can have a substantial public health impact especially reducing severe dengue cases and the need for hospitalization.

The SAGE statements were expected to assure the public, including the various health advocates who appealed to Health Secretary Janette Garin that a more thorough evaluation of the cost-effectiveness and optimal population segment targeting be done first before actual implementation of the program is carried out.

However, some health advocates argue that the DOH and WHO might have missed the specific points the advocates tried to raise. They believed that many of these concerns have not really been answered by the SAGE recommendations, which were at most, general statements on how the vaccine’s overall effects could translate into an actual public health benefit. The SAGE statements stressed thought that the final decision whether a dengue vaccination program should be implemented or not must be based on country- and region-specific factors, as guided by pertinent and updated research data. Herein lies the problem—do we have reliable updated seroprevalence data to serve as guide which of our vast population should be targeted?

According to the SAGE, “the target age for routine vaccination should be defined by each country based on an assessment of dengue endemicity and programmatic feasibility of targeting particular ages. For highly endemic settings (e.g. seroprevalence at nine years of age of approximately 90 percent or greater), vaccination at ninr years of age is projected to maximize impact. In settings where seroprevalence at nine years of age is below 90 percent (but above 50 percent), vaccination at 11-14 years of age is preferable.”

Although dengue fever is endemic in various parts of the country, there should be specific national and regional age-stratified data on its seroprevalence. Based on the extensive clinical trials done in Asian and Latin American countries, the vaccine shows variable effectiveness and safety. Hence, the SAGE pegs its effectiveness and safety to specific seroprevalence data.

A search of the literatures shows only four seroprevalence reports published in 2005, 2006, 2009, 2010; and in all of them, the actual studies were done several years earlier.

Even if we include the study which was funded by the vaccine manufacturer, the dengue seroprevalences were less than 90 percent but more than 50 percent. Furthermore, the seroprevalences were not age-stratified. If we were to use these outdated data as basis for the dengue immunization program, then it should have been limited to the 11-14 years age group based on the SAGE recommendations. The big question though is: Are these data valid bases considering that they’re not updated (they’re 6-10 years old) and they’re not age-stratified?

Hopefully, the DOH has in its possession reliable, though unpublished, data on regional age-stratified seroprevalences which guided them in the dengue vaccination program. Otherwise, they should have these studies done first before carrying out a more extensive nationwide dengue vaccination program. Meanwhile, the more than 100,000 children who received the first dose of Dengvaxia, should have their vaccination completed; and the DOH should have a continuing surveillance program on these children to find out the real-world short- and long-term impact of this first vaccine for dengue.

Vital Signs Issue 86 Vol. 4, April 1-30 2016