Dengue vaccine a ‘game-changer’
FDA approval gives physicians a vital new weapon to battle the potentially patal disease
ALMOST 60 years have passed since dengue was first identified in Thailand, in 1958, and the country has since come up with ways to prevent the disease through education and control of the mosquitoes that carry the virus.
However, dengue continues to afflict people in all provinces, men and women and every age group, throughout the year.
Now, though, the Food and Drug Administration’s approval of a safe and effective dengue vaccine is being hailed as a game-changer in terms of comprehensive prevention.
Any one of four viruses spread by mosquitoes can cause dengue. It is an acute condition that can develop into life-threatening haemorrhagic fever, resulting in bleeding, plasma leakage and complications to other parts of the body, including the brain and liver, which can lead to death within days.
“Over the last decade, the number of deaths from dengue has decreased due to more advanced medical technology,” notes Associate Professor Pratap Singhasivanon, dean of tropical medicine and Mahidol University.
“The number of patients, on the other hand, is increasing, especially among adults.
“Research shows that the overall number of asymptomatic cases is three times higher than symptomatic ones, and these cases are 10 times more likely to transmit the dengue virus via mosquitoes,” he says. “It is thus considered a key issue for public-health surveillance and prevention.”
The disease also hurts the country in economic terms. Thailand has spent more than Bt290 million on treating dengue, second only to Indonesia in Southeast Asia.
Thailand sees 80,000 to 100,000 dengue cases annually, 70 to 100 of them fatal.
It has also been discovered that initial infection with one type of virus doesn’t preclude further infection with the other three types. This can be attributed in part to the above-average number of mosquito larvae found in every part of Thailand.
This year, through August 16, nearly 30,000 dengue cases were reported, mostly among children aged five to 14 and young adults 15 to 24. The number of fatal cases in patients 15 years and up rose to 24, and in younger patients to 17.
The leading causes of death related to dengue include delay in seeing a doctor, taking non-steroidal anti-inflammatory (NSAID) drugs without a prescription, and having other medical problems, especially in adults with obesity or chronic disease.
Dr Panumard Yarnwaidsakul, deputy director-general of the Ministry of Public Health’s Department of Disease Control, suggests “Three steps to prevent three diseases”:
l Keep the house clean, especially places where mosquitoes might gather.
l Remove garbage, in which mosquitoes can breed.
l Keep water containers covered to prevent breeding.
Dr Panumard also recommends keeping well:
l Protect yourself from mosquito bites.
l Watch out for high fever, headaches, body and joint aches, red blotches on the skin, vomiting and stomach-ache.
l Go to hospital when you’re sick or have a high fever.
“The new vaccine is one of the World Health Organisation’s recommended preventive measures for countries with a high percentage of dengue infection rate, including Thailand,” says Associate Professor Tawee Chotpitayasunondh, president of the Paediatric Infectious Diseases Society of Thailand.
“The vaccine now approved for use helps prevent symptomatic cases caused by any of the four types of the virus by 65.6 per cent, reduces severe dengue cases by 93.2 per cent, and hospitalisation by 80.8 per cent.”
The vaccine schedule is three doses, given six months apart, with each dose yielding increasingly preventive results.
“Interestingly, the clinical data indicates the vaccine has 81.9 per cent efficacy in those who have been exposed to dengue, but has a lower efficacy of 52.5 per cent, in those who have never been exposed to dengue prior to vaccination,” says Dr Tawee.
“This is because the vaccine does not consist of a pure dengue virus, but is a mix of attenuated dengue virus and flavivirus, which is non-virulent. It helps the immune system recognise the dengue-infected cells in people who have been exposed to dengue before, boosting the immune system to prevent the four virus serotypes, with better efficacy than in those who have never been exposed to dengue before.
“On the other hand, any of the four serotypes is 100-per-cent virulent. The data imply that the vaccine does not cause dengue infection and therefore is not considered a first-time infection. Thus, it is safe and is approved for prevention by the WHO and Food and Drug Administration of Thailand.”