Should we or should we not continue the government’s dengue vaccination program?
The controversy rages on, as some members of Congress threaten to block the passage of the 2017 budget of the Department of Health (DOH) because of the exclusion of the vaccine from their current active programs.
Doctors and health advocates, led by Dr. Tony Dans, Dr. Mercy Fabros and Dr. Tony Leachon, rose in protest and appealed to the legislators to consider the unresolved efficacy and safety issues of the vaccine.
We tackled this issue twice in our previous Medical Files columns (“A second thought on the dengue vaccine,” April 15; “Rejoinder on the dengue vaccine,” April 22), and we highlighted the “knowledge gap” on the vaccine’s long-term safety, particularly on Year 3 after its administration.
Reviewing the original paper of the clinical investigators of the vaccine published in the New England Journal of Medicine (NEJM), even these experts, who knew the details of the clinical trials, acknowledged that they do not have the answers to the hanging questions. They also stressed the need to continue monitoring cases and do further studies to provide the answers that can increase our confidence in the safety of the vaccine.
No new data
I requested my research staff to see if there were any new findings or follow-through analysis on the initial two phase 3 clinical trials on the Sanofi-manufactured vaccine, and they were not able to find any new published data.
In fact, just a few months ago, Scott Halstead, who is the acknowledged leading figure in dengue research in the past 50 years, reiterated the serious concern on the vaccine—that it may even enhance the development of dengue, rather than prevent it.
“It’s happened. We have a vaccine that enhances dengue,” he was quoted in an article published by the Center for Infectious Disease Research and Policy in the United States.
Antibody-dependent
The vaccine appears to cause antibody-dependent enhancement or ADE, a phenomenon in which the dengue vaccine literally predisposes the dengue-naive recipients of the vaccine to a more severe clinical expression of the disease.
Dr. Halstead was the first to identify this phenomenon, and he explained that in ADE, infection with one of the four strains of the dengue virus produces antibodies to that strain and cross-reactive antibodies to the other dengue strains.
“Over time, you make and keep protective levels of antibody from the initial infection, but you lose the cross-reactive antibodies,” added Dr. Halstead. “That allows a second dengue infection to cause severe illness, including dengue hemorrhagic fever.”
To illustrate that this adverse effect is highly probable, he cited the Cuban experience. In 1977, Cubans, a dengue-naive population, were infected with dengue 1. After 20 years, in 1997, there was an outbreak of dengue 2 in the city of Santiago, and hospital admissions for dengue were reported to be eight times higher for patients previously infected with dengue 1.
A long dengue-free interval is also not reassuring. “The longer the interval (between infection with different dengue strains), the more severe the disease,” warned Dr. Hallstead.
Immune response
A similar phenomenon has also been observed in mothers who’ve had two or more dengue infections. Cross-reactive antibodies are transferred to their babies, devoid of T cells, which are important in the immune response. What happens is that their children can have a more serious dengue infection once they get the virus.
‘Worse than an infection’
“The vaccine is even worse than an infection, because it has all different antibodies that wane over time,” Dr. Halstead warned in the article.
Dr. Halstead and Philip Russell, MD, PhD., the former director of the Walter Reed Army Institute of Research and commander of the US Army Medical Research and Development Command, as well as founding president and chair of the Sabin Vaccine Institute, published an article in the journal Vaccine in February, warning everyone of the highly possible adverse effects of the vaccine.
A five-fold risk of hospitalization for dengue in children five years and younger was a glaring red flag in the published phase 3 clinical trials of the vaccine. According to Dr. Russell, Sanofi Pasteur (the vaccine manufacturer) has failed to directly address this phenomenon.
In short, more clinical trials are needed to find out if the vaccine, which our legislators would like DOH to continue procuring, is really safe or not.
Meanwhile, spending P3 billion pesos for it may not be a good decision.