How Effective is the New HIV Vaccine?

| by National Institutes of Health

In an encouraging development, an investigational vaccine regimen has
been shown to be well-tolerated and to have a modest effect in
preventing HIV
infection in a clinical trial involving more than 16,000 adult
participants in Thailand. Following a final analysis of the trial data,
the Surgeon General of the U.S. Army, the trial sponsor, announced
today that the prime-boost investigational vaccine regimen was safe and
31 percent effective in preventing HIV infection.

"These new
findings represent an important step forward in HIV vaccine research,"
says Anthony S. Fauci, M.D., director of the National Institute of
Allergy and Infectious Diseases (NIAID), part of the NIH, which
provided major funding and other support for the study. "For the first
time, an investigational HIV vaccine has demonstrated some ability to
prevent HIV infection among vaccinated individuals. Additional research
is needed to better understand how this vaccine regimen reduced the
risk of HIV infection, but certainly this is an encouraging advance for
the HIV vaccine field."

"We thank the trial staff in Thailand
and the United States for their years of effort in successfully
conducting this study and the study participants and the people of
Thailand for their long-standing support of HIV vaccine research," Dr.
Fauci adds.

The Thai Phase III HIV vaccine study, also known as
RV144, opened in October 2003. The placebo-controlled trial tested the
safety and effectiveness of a prime-boost regimen of two vaccines:
ALVAC-HIV vaccine (the primer dose), a modified canarypox vaccine
developed by Sanofi Pasteur, based in Lyon, France, and AIDSVAX B/E
vaccine (the booster dose), a glycoprotein 120 vaccine developed by
Vaxgen Inc., and now licensed to Global Solutions for Infectious
Diseases (GSID), based in South San Francisco, Calif. The vaccines are
based on the subtype B and E HIV strains that commonly circulate in
Thailand. The subtype B HIV strain is the one most commonly found in
the United States.

Led by principal investigator Supachai
Rerks-Ngarm, M.D., of the Thai Ministry of Public Health’s Department
of Disease Control, the study was sponsored by the U.S. Army in
collaboration with NIAID, Sanofi Pasteur and GSID. The trial, conducted
in the Rayong and Chon Buri provinces of Thailand, enrolled 16,402 men
and women ages 18 to 30 years old at various levels of risk for HIV
infection. Study participants received the ALVAC HIV vaccine or placebo
at enrollment and again after 1 month, 3 months, and 6 months. The
AIDSVAX B/E vaccine or placebo was given to participants at 3 and 6
months. Participants were tested for HIV infection every 6 months for 3
years. During each clinic visit, they were counseled on how to avoid
becoming infected with HIV.

In the final analysis, 74 of 8,198
placebo recipients became infected with HIV compared with 51 of 8,197
participants who received the vaccine regimen. This level of
effectiveness in preventing HIV infection was found to be statistically
significant. The vaccine regimen had no effect, however, on the amount
of virus in the blood of volunteers who acquired HIV infection during
the study.

"The Thai study demonstrates why the HIV vaccine
field must take a balanced approach to conducting both the basic
research needed to discover and design new HIV vaccines and, when
appropriate, testing candidate vaccines in people," says Margaret I.
Johnston, Ph.D., director of NIAID’s Vaccine Research Program within
the Division of AIDS.
"Both avenues provide critical information that will continue to help
us better understand what is needed to develop a fully protective HIV

NIAID and the collaborating partners are working with
other scientific experts to determine next steps, including additional
research of the RV144 vaccine regimen and the need to consider the
impact of these new findings on other HIV vaccine candidates.

who acquired HIV infection while participating in the Thai trial have
been provided access to HIV care and treatment, including highly active
antiretroviral therapy based on the guidelines of the Thai Ministry of
Public Health.

For more information about the Thai Phase III HIV vaccine trial, please see:

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