Cold Virus Foiled AIDS Vaccine

A promising AIDS vaccine that failed in trials—actually increasing rather than reducing risk of infection—turned out to be ineffective in people who had immunity to a common cold virus, developers reported yesterday. The Merck vaccine contained an altered version of that virus, and study subjects with existing immunities to it saw increased risk of contracting HIV, the the Washington Post reports.

Of 800 test subjects with immunity to the cold virus, 21 contracted HIV, compared with nine given a placebo—a large-enough number to shut down the study, and raise questions as to when, if ever, another vaccine should be human tested. Scientists are debating whether to “unblind” the US portion of the study, revealing which of 3,000 participants received the vaccine. (More AIDS vaccine stories.)