By Laurie Sullivan
Science is coming to the aid of travellers with new vaccines soon to offer protection against three of the world’s most common mosquito-borne diseases – dengue fever, malaria, and Chikungunya fever.
While travellers will benefit directly, it will be the reduction in cases among local people in hard-hit countries that will ultimately lower the risk of infection for international visitors, too.
To date this year, 1324 Aussies have experienced a debilitating bout of dengue fever, 264 have contracted malaria, and 63 have returned home infected with the Chikungunya virus. All of them, except for a small percentage of dengue cases in North Queensland, were contracted during overseas travel.
New malaria and dengue vaccines are being assessed by drug regulators prior to release, while an advanced Chikungunya vaccine is undergoing trials. Each is the result of decades of research.
Preventing bites always crucial
However, they won’t be a magic bullet, Dr Eddy Bajrovic, Medical Director of Travelvax Australia, warned.
“These vaccines won’t offer 100% protection,” he said.
“In fact, their effectiveness varies considerably. So, taking measures to prevent bites and eliminate mosquito breeding sites around their accommodation will always be important for travellers visiting popular holiday destinations in Asia, Africa, the Pacific, the Caribbean, and Latin America.
“If, as promised, these new vaccines are affordably priced so that they’re widely used, they will lower the number of cases and fatalities among local people. And, that will mean fewer cases among travellers, too.”
DENGUE: VIVE LE VACCIN
French pharmaceutical maker, Sanofi Pasteur has announced that it will seek licensing approval for a dengue vaccine next year following a series of large-scale clinical trials involving 31,000 volunteers across 10 dengue-endemic countries in Asia and Latin America. The results were published in the New England Journal of Medicine.
The vaccine's effectiveness against the four dengue virus serotypes – Dengue 1,2,3, and 4 – ranged from 42.3% (type 2) to 77.7% (type 4), for an overall effectiveness of 61%. More encouragingly, it was 95.5% effective against severe disease in those who received at least one dose, and 80% effective against hospitalisation for dengue.
The rise and rise of dengue
Across the globe, the number of dengue cases has risen dramatically in recent decades and over 2.5 billion people – more than 40% of the world's population – are now at risk. According to the World Health Organisation (WHO), an estimated 500,000 people are hospitalised due to severe dengue and around 2.5% die each year.
The world’s first dengue vaccine could be available in the second half of 2015 – several years ahead of rivals. Sanofi has invested more than $1.7 billion into development over two decades and can produce up to 100 million doses a year in a purpose-built plant in southern France.
MALARIA: A WORK IN PROGRESS
The world’s first malaria vaccine has been even longer in the making. After 30 years, British company, GlaxoSmithKline (GSK) said its malaria vaccine, RTS,S is being evaluated by the European Medicines Agency in collaboration with the WHO for use in Africa.
It has been long hoped that scientists could develop an effective vaccine against the mosquito-borne parasitic disease, which kills more than 600,000 people a year – mainly infants in the poorest parts of sub-Saharan Africa.
RTS,S won’t eradicate malaria, which caused an estimated 627,000 deaths in 2012 (mainly among young African children). A final-stage trial in babies aged six to 12 weeks showed it was only 30% effective. GSK concedes RTS,S represents an advance in malaria control, but will need to be used alongside other control measures, such as bed nets and anti-malarial medicines.
GSK has committed to market the vaccine at a low price that covers the cost of manufacture, plus a small return of around 5%, which it will flow back into research and development for second-generation malaria vaccines, or vaccines targeting other neglected tropical diseases.
Philanthropist backs next-gen vaccines, treatments
Meanwhile, US philanthropist Bill Gates is also supporting the development of next-gen malaria vaccines with a $150 million donation to the PATH Malaria Vaccine Initiative and $29 million to the Clinton Health Access Initiative to support malaria elimination efforts in southern Africa and the Greater Mekong sub-region of Southeast Asia.
The Gates Foundation is also targeting a host of neglected infectious diseases transmitted by insects with a donation of $60 million to the Drugs for Neglected Diseases Initiative. The program aims to develop safe, effective, affordable, and easy-to-use treatments for onchocerciasis, and lymphatic filariasis, human African trypanosomiasis, and visceral leishmaniasis.
CHIKUNGUNYA: VACCINE SHOWS EARLY PROMISE
A vaccine against Chikungunya is still some years away, but at least one promising candidate is in development.
And, it can’t come too soon. The mosquito-borne virus causes large-scale outbreaks and so far this year has infected around 888,000 people, including 153 deaths, in a relentless sweep through the Caribbean and the Americas this year.
Last month it returned to the Pacific, with over 3000 people affected by an epidemic that’s already reached French Polynesia, American Samoa, Samoa, and Tokelau, a territory of New Zealand in just weeks.
Clinical trials show promising results
After highly successful animal trials, scientists at the US National Institute of Allergy and Infectious Diseases (NIAID) began limited human clinical trials using a particle vaccine in 2011. Chikungunya-neutralising antibodies were detected in all volunteers following the second injection, with a significant boost of antibodies following the third injection.
The researchers, whose study recently appeared online in the Lancet, said antibodies persisted in all volunteers – even those who received the lowest dosage – for almost a year at levels similar to those seen in recovered patients.
Work is continuing: Unlike its early trial vaccine, NIAID’s next formulation will almost certainly incorporate an adjuvant — a substance added to most vaccines to enhance the immune response in the recipient. That would mean similar results could be achieved using lower dosages, thus reducing costs.
“Clearly, there will be no single solution,” Dr Bajrovic said.
“But, these vaccines could play an important part in reining in diseases that cause enormous hardship and suffering to people in the poorest countries. Even bringing them under control would bring huge benefits in health and economic development.”