The medical history of the 20th century has demonstrated beyond all doubt that infectious diseases can be controlled through vaccination. The eradication of smallpox and the elimination of polio testify to the power of global vaccination campaigns.
When Aids was first recognised in 1981 and the causative virus, HIV, isolated in 1983, it was anticipated that recombinant DNA technology and US Bio-Tech companies would rapidly develop an HIV vaccine. Alas, after 25 years of intense research and over $6bn spent, we still do not have a vaccine against HIV.
So, the report from Thailand which shows that a new vaccine for HIV gave 30 per cent protection against infection is the first piece of good news in this gruelling campaign.
The Thai vaccine comprises two separate components.
The first (the prime) is an injection of live virus, ALVAC, a pox virus distantly related to the virus used in the smallpox vaccine eradication modified to express three genes from HIV, and the second (the boost) is the outer coat or envelope of the HIV. Each of these components has been studied before, without success. However, the combination prime-boost studied in 16,000 subjects in Thailand seems to have reduced the risk of acquiring HIV by 30 per cent.
This result will not be good enough to license this particular vaccine; all current licensed vaccines are more than 80 per cent effective. However, this is the first time that vaccination has led to any protective effect, and the door is now open to understand how the vaccine protected, and then how to improve the vaccine to get a greater protection against HIV.
Vaccines work by stimulating the body’s immune system to generate an immune reaction to the virus, so that when the body is exposed to the virus naturally, they already have a pre-existing immunity, and are protected from infection.
In the case of this Thai HIV vaccine, we do not yet know what type of immunity was associated with the 30 per cent protection seen. This information will, hopefully, be reported at a conference next month in Paris. This information will be critical to future progress. The two components of the Thai vaccine, ALVAC and gp120, are both considered to be relatively weak, and many products exist currently in research labs which are more potent.
Now that the barrier to HIV vaccine has opened a crack, knowledge of the type of immunity should open the door to rapid testing of potentially better HIV vaccine candidates.
Testing these newer products will also be lengthy, expensive and slow.
However, the result of this trial, the first ever protection induced by vaccination in HIV infection, will inject a new optimism into researchers and funders alike.