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20 Oct 2009 10:23
Doctors who surprised the world of Aids research with a study showing a vaccine prevented some HIV infections released details of their findings on Tuesday and said careful review showed they held up.
Full details of the study, which showed the experimental vaccine prevented nearly one-third of infections among 16 000 ordinary Thai volunteers, were published in the New England Journal of Medicine.
“That’s a validation of the results,” said Dr. Jerome Kim, a United States Army colonel at the Walter Reed Army Institute of Research in Maryland, who helped lead the trial.
Kim and colleagues will present details to a meeting of Aids vaccine researchers in Paris on Tuesday.
The vaccine is a combination of Sanofi-Pasteur’s ALVAC canary pox/HIV vaccine and the failed HIV vaccine AIDSVAX, made by a San Francisco company called VaxGen and now owned by the nonprofit Global Solutions for Infectious Diseases.
The trial, sponsored by the US government and the Thai Ministry of Public Health, cut the risk of infection by 31,2% over three years, according to one analysis of the data.
Kim’s team stressed the effect was modest and hard to interpret, that the vaccine was nowhere near ready for commercial use, and may not work in Africa, where Aids is most common.
Days after the results were announced at an unusual news conference in Bangkok in September, some unnamed researchers were quoted by Science magazine and the Wall Street Journal as saying the study was weaker than at first presented.
At issue were the statistical methods used to analyze the data.
Kim’s team did three different analyses—one called an intention to treat analysis, one called a modified intention to treat analysis and one called a pro-protocol analysis.
Kim said the modified intention to treat analysis was the most accurate, as it excluded seven volunteers who were later found to have been infected with HIV before they were vaccinated.
People who questioned the findings, according to the media reports, said the pro-protocol and intention-to-treat analyses were statistically insignificant.
Kim said his team answered questions about this to the satisfaction of the independent reviewers at the journal—a process called peer review that is one of the services provided by medical and scientific journals.
In a commentary in the journal, Dr Raphael Dolin of Beth Israel Deaconess Medical Centre and Harvard Medical School in Boston said the study had been rigorously designed and conducted.
“Although the merits of each type of analysis can be debated, all three yielded a possible, albeit modest, effect of the vaccine in preventing HIV infection,” Dolin wrote.
What is still unclear is how long the protection lasts and how much each of the two vaccines contributed.
“We need to try to understand why we saw what we saw,” Kim said.
Some people who were vaccinated got infected anyway and have as much virus in the system as unvaccinated patients, which suggests that whatever it is in the immune system that protects from HIV infection, it is different from what is needed to control an infection.
The Aids virus infects an estimated 33-million people globally and has killed 25-million since it was identified in the 1980s.
Cocktails of drugs can control HIV but there is no cure.
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