Joseph Mariathasan explores the impact of – and possible solution to – the growing dengue epidemic
Summer is approaching, and as thoughts for many turn to what preparations may be required for holidays in the sun, travellers to tropical regions may be looking at stocking up on malaria tablets. These can, in some cases, have rather nasty side effects, but those travelling to Sri Lanka, for example, may not need to bother, as it may become the first-ever tropical country to eliminate malaria officially (if no one is reported with it by October this year).
However, whilst malaria may be absent in Sri Lanka, and anti-malaria tablets can, if required, be taken for travel elsewhere, there is another mosquito-borne disease – dengue – that travellers need to be aware of. It causes a severe flu-like illness and can sometimes lead to a potentially lethal complication called dengue haemorrhagic fever. The WHO finds that Central and South America, South-East Asia and the Western Pacific are the most seriously affected regions in the world. What that means is that some 2.5bn people – two-fifths of the world’s population – are now at risk of acquiring dengue. That includes countries such as Brazil, currently preparing for the 2016 Olympics, and popular tourist destinations such as Thailand, with upwards of 25m visitors a year.
Estimates of people getting dengue each year are very unreliable, as the symptoms are easily confused with flu and in many cases may be very mild and, as such, unreported. Why dengue is becoming a serious burden for countries is that, according to WHO, up to 50m infections occur annually, with 500,000 cases of dengue haemorrhagic fever and 22,000 deaths, mainly among children. Prior to 1970, only nine countries had experienced cases of dengue haemorrhagic fever. Since then, the number has increased more than fourfold and continues to rise. Some academics have estimated actual dengue cases are probably closer to 400m a year, and there are approaching 100m that have pronounced symptoms. Others have estimated that dengue is now becoming more dangerous than malaria in terms of economic impact and morbidity.
Whilst dengue is becoming a major global health issue, there may also be a solution, or rather, a number of solutions. Vaccines are currently being developed by a number of companies, and clinical trials are well under way. The illness itself is caused by one of four variations (serotypes) of a virus. Catching one serotype gives a person immunity for life to that specific serotype. However, it also appears to raise the chances of complications if there is a subsequent infection by a different serotype, and that can result in dengue haemorrhagic fever, which can be fatal. Therefore, any vaccine has to be effective against all four serotypes to give complete immunity.
Given dengue’s economic impact, it is unsurprising there is a race to develop a dengue vaccine. Whoever succeeds will potentially save countless lives and alleviate much misery but also profit from an immense market opportunity. What is encouraging for everyone, including investors, is that there does appear to be a real chance of success within the next year or two. Currently, Sanofi Pasteur, the vaccines division of French pharmaceutical company Sanofi, has received a fair amount of attention because it has announced results for clinical trials of a vaccine that shows an overall efficacy against any symptomatic dengue disease of 60.8% in children and adolescents.
Whilst this may not sound like a solution, it reported a 95.5% protection against severe dengue and an 80.3% reduction in the risk of hospitalisation during the study. Sanofi Pasteur itself is so confident of its vaccine that it has built a new vaccine-manufacturing facility in France with the objective of reducing the time necessary to provide access to the vaccine once it is licensed. It became operational in 2014 with a production capacity of 100m doses of the vaccine per year. Sanofi, though, is not the only firm working on vaccines. It is highly likely that, within the next year or two, there will be announcements of breakthroughs by firms such as Japan’s Takeda Pharmaceutical, which is undertaking phase-III clinical trials in Sri Lanka and four other Asian countries. The race for a successful dengue virus is well and truly under way.
Joseph Mariathasan is a contributing editor at IPE