Competitive Exams: Current Affairs 2011: Dengue Vaccine

Dengue Vaccine

Dengue, according to the World Health Organisation, is the most rapidly spreading mosquito-borne viral disease in the world.

In the last five decades, the incidence has jumped 30-fold. The disease is now endemic in over 100 countries, placing two-fifths of the world's population at risk.

Not only is the number of cases increasing as the disease spreads to new areas but explosive outbreaks are occurring, the global agency notes.

Over the years, dengue has become endemic across much of India. But to keep the death rate down, it is essential that signs of severe forms of the disease, such as a rash and small bleeding spots on the skin, be recognised. Such people must be immediately admitted to a hospital that can provide supportive treatment, he says.

However, hospitals can become heavily burdened when a large number of people become infected during outbreaks.

While vaccines are available against yellow fever and Japanese encephalitis, caused by closely related viruses, a vaccine against dengue has proved remarkably hard to develop. Nevertheless, a number of different approaches to producing vaccines against it are being tested, from live but weakened viruses to killed viruses, and giving bits of viral protein. Some of these are already in clinical trials.

One hurdle to any prospective vaccine is that the virus comes in four varieties known as serotypes. A person who recovers after being infected with one serotype develops lifelong immunity only to that form of the virus, not the others.

The paradigm has been to make a vaccine that contains the four different viruses and get simultaneous immunisation against each of them.

Dengue has the most amazing perversion of the immune response. The cells that were supposed to scout out and kill the viruses as well as the antibodies that were supposed to destroy them were forming an unholy complex to defeat the immune system.

Thai scientists have successfully produced the world's first dengue hemorrhagic fever vaccine and will let the private sector improve it for the effective treatment of patients. The Thailand Ministry of Science and Technology has introduced the world's first live attenuated dengue hemorrhagic fever vaccine developed by

Thailand researchers.

This was achieved by combining attenuated DNA with a protein structure that stimulates immunity against the dengue hemorrhagic fever caused by the present strain of the dengue virus. The newly developed vaccine is expected to better protect people from the dengue hemorrhagic fever.

But the challenge of developing a dengue vaccine may not end with successfully completing human trials and getting a licence for public use.

Trials will need to address the risk of persons acquiring or developing severe dengue as a direct consequence of vaccination, noted a summary of a WHO

Technical Consultation published in the journal, Vaccine, in 2008. Long-term follow-up of those who participated in vaccine trials would be a powerful way of conforming or rejecting such a risk. Such follow-up should be planned in advance, it said.

Dengue vaccine, more than almost any other, is going to require sustained, longterm follow up:

If a safe and effective vaccine becomes available, it would be possible to consider immunising children and young adults in parts of India where the disease is endemic. It is people in these age groups, rather than older adults, who are the most affected by severe forms of dengue and among whom most of the mortality occurs.

Courtesy: The Hindu and Times of India