WASHINGTON (Reuters) – The flu drugs Tamiflu and Relenza may not be worthwhile to treat seasonal influenza in healthy adults, British researchers reported on Friday.

“Recommending the use of antiviral drugs for the treatment of people presenting with symptoms is unlikely to be the most appropriate course of action,” wrote Jane Burch of the University of York and colleagues.

Their study, published in the Lancet Infectious Diseases, supports an advisory from the World Health Organization that says healthy patients who get H1N1 swine flu without suffering complications do not need to be treated with antivirals.

Tamiflu, made by Switzerland’s Roche under license from Gilead Sciences Inc., is a pill that can both treat and prevent influenza A viruses of all kinds. Zanamivir, made by GlaxoSmithKline under license from Australia’s Biota and sold under the brand name Relenza, is an inhaled drug in the same class.

WHO strongly recommends both drugs for pregnant women, patients with underlying medical conditions and children under 5, as they are at increased risk of more severe illness.

Burch’s team reviewed many different published studies on Tamiflu and Relenza. “We present the results for healthy adults and people at-risk of influenza-related complications,” they wrote.

Both drugs shaved about half a day, on average, off the time patients were ill, they found. Influenza usually affects people for about a week.

The drugs worked a little better in people who have a high risk of complications, such as patients with diabetes or asthma, with Relenza cutting sickness by almost a day and Tamiflu by three-quarters of a day, on average.

This suggests the drugs should be reserved for people who need them the most, the researchers concluded.

Many countries have stockpiled both drugs. H1N1 swine flu has been declared a pandemic and is circulating globally. U.S. health officials said on Friday it was worsening in Japan, getting better in Britain and was still widely active in the United States.

Flu is rare in all three countries in August.

Global manufacturers do not expect to have vaccines ready until the end of September or October at the soonest.

(Editing by Chris Wilson)