BASEL, Switzerland -- Swiss drugmaker Novartis AG said Thursday it is on track to meet its U.S. government order for swine flu vaccine, seeking to calm fears in recent weeks that shipments and vaccination programs may be delayed.

The Basel-based company said it already has delivered more than 7.5 million doses of vaccine for the A(H1N1) flu that the World Health Organization vaccines declared a pandemic in June.

Novartis said it expects to send 25-30 million doses to the United States by the end of November.

"If you look at the U.S. market, there's been a lot of confusion around about how much was to be delivered by when," said spokesman Eric Althoff. "In fact, we're exactly where we told the government we would be."

U.S. authorities said earlier this month they had received only about 23 million of the predicted 45 million vaccine doses from Novartis and other vaccine makers by mid-October. The delay has caused many U.S. states to postpone mass vaccinations, and worried patients have bombarded doctors with calls asking when a shot would be available.

"It's made a lot of headlines in the U.S.," said Althoff. "Every contract takes into account that you're making a commitment with many unknown variants, and one of the variants was the yield, which then delays the amount of vaccine available at one given time."

In fact, the amount of seed virus Novartis was able to produce was initially far below expectations, though the yield has since been increased, said Althoff.

"The (U.S.) government has always been updated on this progress," he said.

Novartis shares were down 0.9 percent at 52.85 Swiss francs ($51.53) on the Zurich exchange Thursday.