Drugmakers say they are on track to deliver as much H1N1 swine flu vaccine to the United States as they promised, despite concerns over production.

The U.S. has contracted with its five suppliers of seasonal influenza vaccine to also deliver H1N1 vaccine, but officials have sharply cut initial estimates of how much will be delivered this month and next.

Many U.S. states and cities say they have received about a tenth as much vaccine as they had expected by this time, but Novartis AG and AstraZeneca Plc said they were on track to meet their commitments.

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.

In September, U.S. officials said 40 million vaccine doses would be available by the end of October and they estimated 20 million doses a week would be delivered, with a goal of 250 million doses by the end of flu season in March or April.

Not only did we complete our commitment to provide seasonal vaccine ahead of schedule, we are making every effort to make as much H1N1vaccine available as quickly as possible, Novartis vaccines chief Andrin Oswald said in a statement.

GlaxoSmithKline Plc Chief Executive Andrew Witty said on Wednesday his company had initially experienced problems, 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 U.S., since it is still awaiting approval for its unadjuvanted vaccine from U.S. regulators.

Sanofi has said it is on track to deliver more than 75 million doses to the United States.

LOW YIELDS

Novartis said production was progressing despite low yields of the initial seed virus. 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, in line with commitments it made to U.S. authorities. 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.

As requested, Novartis is supplying the U.S. 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.

AstraZeneca's Chief Financial Officer Simon Lowth said it had already delivered 10 million doses of H1N1 vaccine to the U.S. and was on track for a total of 40 million by early 2010.

Unlike other vaccine firms, AstraZeneca's MedImmune unit supplies flu vaccine as a nasal spray rather than injection and uses a different system to make the vaccine.

It has not had problems with vaccine yields but is constrained by the number of spraying devices that can be manufactured.

MedImmune, which could produce about 200 million doses of its needle-free vaccine in bulk, is now talking to regulators about perfecting a dropper device to drip vaccines into the nose -- technology that has been used with other vaccines.

In early afternoon trade Novartis shares were down 0.37 percent, Sanofi-Aventis down 1.73 percent, Glaxo down 0.72 percent, and Astra Zeneca down 1.76 percent.

Medicine