Antivirals work best if given within 24 to 48 hours. (CBC)

Antiviral drugs for swine flu patients may be wasted on the elderly in some cases, but treating younger people could help save lives, Italian researchers say.

Writing in the journal BMC Infectious Diseases, the researchers said their mathematical model suggested giving antiviral drugs to the elderly would not significantly reduce mortality and may lead to an increase in resistance.

So far, antivirals are the most effective intervention in the H1N1 flu pandemic, as no vaccine is currently available, said study author Stefano Merler of the Bruno Kessler Foundation, a research organization in Trento, Italy.

But for antivirals to work, countries need to stockpile large amounts of doses.

"Our work demonstrates that even in countries where the antiviral stockpile is not sufficient to treat 25 per cent of the population, the minimum level suggested by the [World Health Organization], it is possible to reduce morbidity and excess mortality by prioritizing the use of antivirals by age," Merler said in a release from the journal's publisher, BioMed Central.

"Although a policy of age-specific prioritization of antiviral use will be controversial ethically, it may be the most efficient use of stockpiled therapies."

Italy, for example, only has enough drugs to treat 12 per cent of its population. By combining Canada's antiviral stockpile, emergency supplies and other stores, officials estimate there is enough to treat about one-quarter of the Canadian population.

Obtaining early estimates of the overall impact of the epidemic and age-specific death rates could prove important in optimizing use of antivirals, the researchers concluded in the study.

The model looked at the effects of flu outbreaks of varying virulence. Depending on how the virus behaved, treating people over age 65 may not lead to a significant reduction in the total number of cases, while treating those over the age of two would, the study suggested.

Early detection key

The researchers also suggested that health officials do a better job of diagnosing, tracking and treating cases quickly, since the antivirals work best if given within 24 to 48 hours.

"Our study also highlights the importance of the early detection of cases," they wrote in study.

"In fact, great effort should be made in order to establish a surveillance system able to detect and treat cases as soon as possible since a delay of more than 24 hours could make both antiviral treatment and prophylaxis very inefficient."

Two antiviral medications, zanamivir, sold under the brand name Relenza, and oseltamivir, sold under the brand name Tamiflu, are included in stockpiles.

Both drugs can reduce the risk of death among people at serious risk of flu complications, including those over 65, the very young, people with asthma and other chronic diseases and pregnant women.

Most health officials recommend using the drugs to prevent infection only for people who are at high risk of complications and have been in close contact with someone confirmed to be infected.

Vaccine needs

Health officials are also weighing who should be first to get swine flu shots when there aren't enough for everyone. It's expected there will be a global shortage of potential swine flu vaccine, due in part to less than expected yields from manufacturers growing it in eggs.

"We will be ordering enough vaccine for those Canadians who at this point in time we anticipate will want and need the vaccine," Dr. Arlene King, Ontario's chief medical officer of health, said Monday.

"We are working through who are the groups that are at risk, how many people have already been exposed and thus don't need it," added Allison Stuart of Ontario's Ministry of Health. Blood samples from Quebec and British Columbia will also be reviewed to determine how many people have already been infected and are therefore immune.

On Wednesday, a federal vaccine advisory group will meet in the U.S. to determine who should be first in line for swine flu shots. Health care workers are at the top of the list, and pregnant women could also be included since they have suffered and died from the swine flu at disproportionately high rates.

An estimated 816 people have died with swine-flu infections to date, according to the WHO's latest tally. As of Monday, the number of deaths in Canada related to swine flu was 57.