The WHO said this week it was up to U.S. government officials to decide whether to extend the expiration of first-line swine flu treatment Tamiflu by two years, as Roche is urging health officials to do.

The U.S., Canada, the European Union, Australia and Hong Kong have already pushed back Tamiflu's expiration date to seven from five years, after Roche showed that the drug's active ingredient is more stable and long-lasting than Roche initially said it was.

Meanwhile, WHO is urging that Tamifu be given only to pregnant women and to patients who are at high risk for pneumonia, since most people infected with the H1N1 (swine flu) virus suffer mild symptoms and recover rapidly. School kids may also be among the first to be vaccinated, since children who are contagious can spread the virus widely among their peers.

Vaccine Capacity Delayed

Meanwhile, WHO says it has no idea of how much vaccine will be available for the possible swine flu pandemic that could return to the Northern Hemisphere as a more virulent bug when the cold weather hits in mid-October.

Vaccine makers say that because the CDC initially gave them flu strains that were too weak to yield sufficient product, they are facing production delays.

WHO says that vaccine supply will hinge on whether one shot or two is needed. Officials believe two shots will be necessary to confer full flu protection. Currently, scientists who are testing the vaccines in clinical trials are trying to find the right dosage.

According to a CBS News report, U.S. officials had said they expected to have 120 million doses of swine flu vaccine ready in mid-October. CBS News says experts are currently predicting that only 45 million doses will be ready, with another 20 million shots ready every month after that.

Sources: WHO, CDC, Roche, CBS News