An experimental vaccine that reduced the risk of HIV, the virus that causes Aids, by one-third in the people immunised made headlines across the world a fortnight ago. Most people wondered why. Sure, the biggest ever Phase-III trial done to test the safety and effectiveness of an HIV vaccine on humans showed 31.2 per cent lowered the risk of HIV infection among 16,000 healthy men and women in Thailand. But far too many ‘ifs’ remained.
One, it was obvious that the vaccine was still experimental, and needed a lot of tinkering before it could go into production, if at all. Two, it did not offer protection to the majority — 68.8 per cent — of the people inoculated.
Finally, the vaccine is designed to offer protection against HIV-1 subtype B, predominant in the US and Europe, and subtype E, common in Thailand and South East Asia. At this stage, scientists admitted they could, at best, just hope for the vaccine to work against HIV-1 subtype C, found in Africa and South Asia, regions where new infections are the fastest-growing in the world. Till clinical trials were done among these populations, we would not know. And if the trials did take place, they would take years, just as the Thailand trial took six years.
The reason for the euphoric response was simple: the success in Thailand came after a series of failed vaccine trials that made many scientists question whether a vaccine against HIV was possible at all. The Thailand results showed that for the first time in 26 years a vaccine could prevent infection in many of the estimated 6,800 people who get infected with HIV every day.
There are 33.2 million people with HIV in the world; 2.1 million of them are children. Vaccines against HIV have, at best, shown no effect. At worst, one large international trial even indicated an increased risk of HIV infection among the people vaccinated. The past two years — 2007 and 2008 — have been particularly disappointing, with two large large clinical trails being abandoned.
“If there is one area of the science of HIV that is still quite problematic, that has to do with vaccines,” said Anthony Fauci, director of the US National Institutes of Allergy and Infectious Diseases, in 2008 when he announced the discontinuation of the ambitious vaccine trial called PAVE 100 that had planned to enroll 8,500 volunteers in the US, South America, the Caribbean and eastern and southern Africa. “We have a lot of money, we have a lot of brilliant people thinking about it, why is it so difficult? The reason is that HIV is different — namely, the natural [human] immune response to HIV is inadequate.”
In 2007, the STEP HIV vaccine study was stopped after it was found that the experimental vaccine used (developed by Merck & Co. Inc) failed to prevent HIV infection or reduce viral load used to measure the severity of disease. In early 2004, the STEP trial had enrolled and vaccinated 3,000 healthy volunteers in Australia, Brazil, Canada, the Dominican Republic, Haiti, Jamaica, Peru, Puerto Rico and the US. In 2007, an independent data and safety monitoring board said the STEP study vaccine did not prevent HIV infection or affect severity of infection in those who became infected with HIV. And some of the immunised volunteers were found to be at a greater risk of getting HIV infected if they were naturally exposed to HIV.
The Thailand vaccine worked differently, using as it did a two-vaccine combination in a ‘prime-boost’ approach. If the immune response for the Thailand vaccine could be successfully heightened, said scientists gleefully, the vaccine will take another five years to hit the market. And when it does, governments need to ensure it reaches those who need it the most: adolescents and young adults, who are at most risk. The stigma around Aids may make it difficult to reach them — more so in India, where many people still believe HIV infection happens to impure people and the bold and young need little more than prayer and yoga to protect themselves against nasty viruses such as HIV.