Nearly a year after the commencement of the Phase I clinical trial of an AIDS vaccine candidate in Pune, a similar trial on another vaccine candidate was initiated recently in Chennai by the Government of India and the International AIDS Vaccine Initiative (IAVI) combine. The second trial follows the suggestion of President Abdul Kalam that one more AIDS vaccine candidate be considered. This is the beginning of a strategy to test several vaccines in parallel rather than sequentially, which may greatly reduce the time taken to find an effective vaccine. Nearly a year’s time has already been saved by heeding the President’s advice, as the initial plan was to start the vaccine trial in India using Modified Vaccine Ankara (MVA) vector for carrying six genes of HIV. But with the MVA vaccine and related dossiers not ready last year, the trial at the National AIDS Research Institute (NARI) in Pune was started using the Adeno Associated Virus (AAV) vector that was under Phase I clinical trial in Germany and Belgium since December 2003. The Chennai clinical trial will be using the MVA vector. Though the vector used is a live one, it is in a highly weakened form and considered safe as it is not known to replicate in human cells. While the percentage of the Indian population that is naturally infected with the AAV and hence has developed antibodies against the vector is not known, the MVA does not naturally infect humans. But immune response against the MVA vector would be seen in those who have been immunised against smallpox.
The start of the Chennai trial coincides with the successful enrolment of all the 30 volunteers for the Pune trial. The completion of enrolment process can be considered significant as it shows that it is indeed possible to get volunteers for such a sensitive trial if it is done ethically. While the volunteers for the phase I trial belong to the category with a low risk of getting infected with HIV, the real challenge will come when the clinical trial enters the Phase III stage involving high-risk category people who are not infected. While the vaccine’s efficacy can be tested only when the volunteers engage in high-risk behaviour, ethics demand that they be counselled against such behaviour. How well those involved in the trials accomplish this delicate task and take care of those who get infected in the process will determine the future success of AIDS vaccine trials. Like in the case of the vector used in the Pune clinical trial, the MVA vector is likely to protect individuals from progressing to a diseased state by reducing the viral load even if it is unable to prevent individuals from getting infected. While a successful vaccine may be eight to ten years away if things go well, the primary focus should still be on prevention strategies. For quite some time to come, preventive strategies are going to be by far the simplest and most efficient ways of keeping AIDS in check.