Swiss drugmaker Novartis AG is on track to deliver pandemic H1N1 swine flu vaccine to the United States in line with its commitments, despite low yields of the initial seed virus, it said on Thursday.

Many U.S. states and cities say they have received about a tenth as much vaccine as they had expected by this time and the delays may discourage people who are lining up to get their shots, officials have said.

Novartis said it will produce 90 million units of bulk antigen, which is expected to result in 60 million finished vaccine doses, due in part to overfills in the filling process.

It has already shipped more than 7.5 million doses and expects to reach 25 to 30 million by the end of November.

LiveShots Blog: H1N1

Full Coverage H1N1 — Click here

How to Avoid Getting the Flu

"The deliveries are in line with commitments made to the U.S. Department of Health and Human Services," the group said in a statement.

As requested, Novartis is supplying the United States with unadjuvanted vaccine, which does not contain an additive. But it is has also started delivering its own adjuvant, which could be used with the vaccine to double the number of doses produced.

Initially, Novartis was achieving only 23 percent of the average yield obtained with seasonal vaccines when it started making H1N1 shots. But the company said it had been using a new seed virus since the middle of September, which provides an improved yield of 63 percent.

To date, 42 million bulk units of vaccine have been produced and the full run of 90 million is expected to be completed by December.

Most major vaccine producers have been struggling with low H1N1 yields, leading to lower than expected shipments and a scramble for supplies in some markets.

GlaxoSmithKline Plc Chief Executive Andrew Witty said on Wednesday his company had experienced similar problems early on, but yields were now improving and he predicted the final yield would be "pretty good" compared with historic flu strains.

Glaxo is one of the world's largest manufacturers of flu vaccines, along with Sanofi-Aventis and Novartis. It is not, however, a big source of vaccine for the United States, since it is still awaiting approval for its unadjuvanted vaccine from U.S. regulators.