Mexico has decided to approve the use of a vaccine against the dengue virus. This is the first vaccine to be actually used to protect against contracting dengue fever, and Mexico is the first country to officially authorise its use. The vaccine is now approved for use after going through trials involving 40,000 persons and will be given initially in Mexico to persons between the ages of nine and 45. It will be administered in areas where dengue fever is endemic, that is, prevalent.
The development of the vaccine is a welcome advancement in public health and is certainly good news for parts of the world including the Caribbean, where dengue is endemic. The vaccine named Dengvaxia was developed by French pharmaceutical company Sanofi, which has declared it “a historic milestone for our company, for the global public health community and, most importantly, for half the world’s population who lives at risk of dengue.” The company took 20 years to develop the vaccine.
Dengue fever seems to be seasonal in our region. There are periodic outbreaks of the disease. It is spread by the Aedes aegypti mosquito so the outbreaks in the Caribbean usually correspond to wet weather and conditions favourable for increased breeding of mosquitos. When severe, dengue fever can lead to hospitalisation. Around the world, approximately 22,000 deaths annually are attributable to the disease. The disease itself is very debilitating, especially as the symptoms are painful as indicated by its secondary name of “break bone fever.”
Most people who contact dengue always recall the pain more than anything else. The public health burden of dengue fever is considerable considering the large numbers of persons usually affected, which the World Health Organisation (WHO) estimates at 400 million globally. It could cause strain on healthcare capacity during times of the year when the incidence of the disease is high. Additionally, it would have an economic impact on productivity during outbreaks as large numbers of persons are usually affected, and the nature of the disease would reduce the ability of affected persons to carry out their normal work.
The vaccine will protect against the four strains of dengue, including the most severe type known as dengue haemorrhagic fever, which can cause organ failure and internal bleeding. However, the effectiveness of the vaccine is just 60.8 percent which is not as effective a rate as in some other vaccines which can have up to 95 percent effectiveness. Sanofi says in their trials, the vaccine “prevented nine out of 10 cases of severe dengue and eight out of 10 hospitalizations due to dengue” in the nine-16 age group.
Considering that, according to the WHO, the severe form of the disease (dengue haemorrhagic fever) is the leading cause of illness and death in children in some Asian and Latin American countries, the results for this age group suggest that it would be a useful treatment for children. Some of the concerns regarding the treatment of dengue fever are its rapid spread into parts of the world where it was originally unknown and the fact that it has four different strains of the virus. Changing weather patterns are believed to be contributing to the geographical spread of the disease. More travel and interaction of persons is also a contributing factor.
Before 1970, only nine countries had experienced severe epidemics. Dengue is now prevalent in more than100 countries, according to WHO information. The different strains of the virus make it possible for persons to be infected more than once. If you contract one type of dengue, you will never get that type again, but this immunity will protect only for a while against the other types of dengue. There is also the belief that repeated infections could lead to contracting the most severe form of the disease. In this regard then, the vaccine would overcome that immunity concern as it protects against all four strains of the disease.
While the areas of the world most plagued by the disease may welcome the arrival of a vaccine, the cost of the vaccine would be an important consideration. There is no information from Sanofi on the cost of the vaccine. The current interventions of use of insecticides, reducing potential mosquito breeding sites around the home and in communities and other control measures should not be abandoned. It is better to have a two-pronged approach of prevention and treatment. It should be noted too that the trial had only included persons nine to 45 years. Dengue can infect all age groups so other measures to reduce the spread of the disease have to be maintained.
The use of the vaccine may have an impact in that it would reduce the number of infected persons who can therefore spread the disease. Meanwhile, attention should remain fixed on the Aedes aegypti mosquito and reduction of its numbers. This is not just important for control of dengue fever, but the same mosquito is also the carrier of the virus for yellow fever, chikungunya, and zika. The latter two previously unknown have reached us here in the Caribbean. So the fight against the mosquito itself must continue as vaccines can take decades to be developed. Controlling the mosquito will help to control the spread of all the various diseases that it helps to transmit.
Dengue sufferers and healthcare officials will be watching to see how Mexico fares with the use of the new vaccine. If Mexico reports significant positive impact, other countries may be persuaded to adopt the use of Dengvaxia. For some, of course, the cost will always be an important factor to consider compared with the benefits, as some countries may have more burdens on the healthcare system than others. Some may have fewer numbers of persons requiring hospitalisation. Each country would have to make decisions relevant to the impact of dengue on their populations. Despite all the considerations, those persons who have ever suffered from dengue fever are probably wishing that the vaccine had been available earlier.
Contributed by Terry Nisbett
