US activist group urges caution on vaccine trial results

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The results of the RV 144 HIV vaccine trial should be treated with caution until further data are presented, US advocacy organisation Treatment Action Group said on Friday, following the announcement that the combination of vaccines used in the study resulted in a 31.2% reduction in the risk of HIV infection.

“Based on the limited amount of information that has been released, it appears that the statistical significance [of the result] hangs on very few cases of HIV infection. TAG urges caution in interpreting the findings until more detailed information is available,“ the group stated in a press release.

Seventy-four out of 8198 volunteers in the placebo group became infected, compared with 51 out of 8197 volunteers who received a combination of two vaccines, ALVAC vCP1521 and AIDSVAX B/E. Participants in both the vaccine group and the placebo group received counselling on how to reduce their risk of HIV infection.


statistical significance

Statistical tests are used to judge whether the results of a study could be due to chance and would not be confirmed if the study was repeated. If result is probably not due to chance, the results are ‘statistically significant’. 


A pill or liquid which looks and tastes exactly like a real drug, but contains no active substance.


In HIV, different strains which can be grouped according to their genes. HIV-1 is classified into three ‘groups,’ M, N, and O. Most HIV-1 is in group M which is further divided into subtypes, A, B, C and D etc. Subtype B is most common in Europe and North America, whilst A, C and D are most important worldwide.


How well something works (in a research study). See also ‘effectiveness’.


The outer surface of a virus, also called the coat. Not all viruses have an envelope. In the case of HIV, the envelope contains two viral proteins (gp120 and gp41), which are initially produced as a single, larger protein (gp160) that is then cleaved in two. 

Although the difference in the risk of infection was statistically significant, the confidence intervals for the estimate were extremely wide.

Confidence intervals represent the range of values within which the efficacy could lie, according to statistical methods.

In this study, the confidence intervals ranged from 1.1% to 52.1%, suggesting at the lower limit the possibility that the vaccine was only 1.1% more effective in preventing infection than risk-reduction counselling alone.

Further results from the study will be presented at the International AIDS Vaccine conference in Paris, October 19th-22nd.

Data on the immunological correlates of protection from infection in study participants will be amongst the subjects reported, but investigators have warned that due to the small number of infections in the study, they will have limited ability to carry out sub-group analyses to determine the effects of gender, risk group or other variables on the risk of infection.

Trial investigators have also warned that the results should not be over-interpreted. In a conference call with journalists on Thursday, Dr Anthony Fauci emphasised that the vaccine construct used in the study, which used the viral envelope proteins from subtype B and E in order to stimulate antibody production, had been tailored to the types of HIV most commonly circulating in Thailand.

Quite different vaccines would need to be constructed for other regions of the world if the approach tested in this study were eventually deemed to be worth investigating in wider studies.

Further analysis of the study results is available here.

Background information on the study is available here, and information on the topic of HIV vaccine research is available here.