Researchers Add New Drug Prophylactic Option Against Flu

ALEXANDRIA, Va. -- Didn't get your flu shot this season? A study published in the Feb. 1, 2004 issue of The Journal of Infectious Diseases supports the efficacy of an adjunct to influenza vaccination.

Researchers examined the common influenza season scenario of a household in which a family member was infected with influenza virus. They found that when the family member with influenza was treated with the antiviral drug oseltamivir, post-exposure oseltamivir prophylaxis of all other family members significantly reduced the frequency of virus transmission and illness in the household. Because households are important sites of influenza virus transmission, these results have implications for the management of influenza outbreaks in the community.

The prospective, open-label, randomized study was conducted in multiple centers in Europe and North America by Frederick G. Hayden, MD, of the University of Virginia and colleagues. They studied a total of 277 households with a suspected influenza introduction during the 2000-2001 season. These households had 298 ill index cases, 62 percent of whom were shown to be influenza-infected, and 812 contacts aged one year or older. In all households, the ill index member received a five-day course of oseltamivir treatment. In one-half of these households, the contacts received post-exposure prophylaxis with once-daily oseltamivir for 10 days; in the other half, the household contacts received treatment only if they developed symptoms of illness.

The researchers found that post-exposure prophylaxis combined with treatment of the ill household member was more effective in preventing subsequent influenza illness in contacts than treating the ill family member only. For all enrolled households, the protective efficacy of the post-exposure prophylaxis strategy was 63 percent, and prophylaxis reduced the number of individual contacts with laboratory-confirmed influenza illness by 73 percent.

Among other notable findings, the authors reported that oseltamivir was generally well tolerated in children and adults, although associated with some nausea and vomiting, and provided protection against illnesses caused by both influenza A and influenza B viruses. Oseltamivir use was not associated with transmission of drug-resistant virus, which had been a problem with some other antiviral drugs, the M2 protein inhibitors amantadine and rimantadine, when used for treatment and prophylaxis of influenza. However, early occurrence of illness in this study indicated that the treatment must be initiated quickly for optimal protection.

Hayden and colleagues noted that although oseltamivir post-exposure prophylaxis for influenza is not a substitute for vaccination, it may be valuable in certain situations because it affords immediate protection. They added that such situations include if vaccines are not available, in conjunction with vaccination late in the influenza season, before vaccine has induced an immune response, or if there is no immune response to the vaccine.

Source: Infectious Diseases Society of America (IDSA)