Efforts to make an HIV vaccine were dealt a severe blow in September when a 3,000-person trial of a Merck vaccine failed. An analysis later showed that that not only did the vaccine fail to protect against HIV, it may have made some trial participants more susceptible to the virus. One theory, currently under investigation, is that a cold virus used in the vaccine to help stimulate the immune system may have somehow stimulated HIV replication, rather than provoking a defense against HIV. An examination of the theory is to be presented at a conference in February.

Meanwhile, other vaccine trials using the cold virus “vector” have been slowed down. Most other potential HIV vaccines in the pipeline are in more rudimentary stages of development. Seth Berkley, director of the International AIDS Vaccine Initiative, said that during vaccine trials, researchers now recommend that all male participants get circumcised as part of the preventive effort. “It ought to be done, but you can’t cram it down peoples’ throats,” he said.