HIV Vaccine Fails in South African Test

By Reuters Staff

March 25, 2021

NEW YORK (Reuters Health) - An experimental vaccine designed to block infection with HIV has failed in a South African study of more than 5,400 volunteers.

The phase 2b-3 trial of the vaccine, known as ALVAC-gp120, followed people over 24 months, during which 138 (or 5.1%) in the vaccine group developed HIV compared to 133 (or 4.9%) of placebo recipients (P=0.84).

Vaccinations were halted in January, 2020, after the study met the pre-specified criteria for non-efficacy.

A previous trial, known as RV144, conducted in Thailand from 2003 to 2009, which used a similar vaccine, had produced results suggesting a modest efficacy of 31.2% against the AIDS virus. However, the effectiveness of that vaccine was only temporary.

The South African study, known as HVTN 702, tried to protect volunteers against a different variant of HIV-1 that was circulating in the region.

Both vaccines employed a canarypox vector.

In an editorial in the New England Journal of Medicine, where the South African study appears, Dr. Mark Feinberg, president of IAVI, a nonprofit scientific research group also known as the International AIDS Vaccine Initiative, said several reasons may explain why the new test showed even less efficacy than the Thai study.

There may be "vaccine-related differences in both the canarypox vector and recombinant gp120 components that were used, differences in the adjuvant that was used, or both; virus-related differences, including a greater circulating viral diversity in South Africa than in Thailand; and differences in the trial population, including a higher infection incidence and potential differences in risk behaviors and host susceptibility," Dr. Feinberg said.

SOURCES: and The New England Journal of Medicine, online March 24, 2021.