By November, the U.S. will have only half the doses of H1N1 swine flu vaccine originally predicted, officials from the Department of Health and Human Services now say.

By Oct. 15, the U.S. now expects to have 45 million doses of the new vaccine on hand. Every week after that, another 20 million doses should roll in until the nation has all 195 million doses it's contracted for from five vaccine makers.

This means that at the end of October, there should be 85 million doses -- just over half the 160 million doses predicted by that date.

There was always an asterisk next to the prediction of 160 million swine flu doses by November. That's because vaccine production is a multi-step process in which a lot can go wrong.

Officials originally felt smug when it turned out that the original H1N1 swine flu vaccine seed strains didn't grow well -- that was included in their prediction.

But there have been new setbacks:

• Four of the five manufacturers providing the vaccine to the U.S. took longer than expected to produce the vaccine's key ingredient.
• One of the five manufacturers is still finishing up production of seasonal flu vaccine, which must be completed before switching to H1N1 swine flu vaccine production.
• It's taken longer than expected to develop potency tests for H1N1 swine flu vaccine.
• One of the manufacturers -- Australia's CSL, under contract to provide 19% of the U.S. supply -- won't be sending vaccine to the U.S. until it has fulfilled demand in Australia, where flu season is in full swing.

There's good news from MedImmune, which makes the live attenuated flu vaccine called FluMist. Production is ahead of schedule on the H1N1 version of this vaccine, which is administered by nasal inhaler. The snag here is that there aren't enough inhalers for all the new doses. The FDA must give the nod to giving the vaccine in the nose-drop form tested in early clinical trials.

By the end of the year, the U.S. will have all 195 million H1N1 swine flu doses it originally ordered. Whether that's enough, or too much, depends on demand.

Right now, the U.S. is bracing for a resurgence of the pandemic. The new flu strikes young people most often, and schools and universities across the nation are opening. All flu bugs like cool dry air -- and fall weather is on the way.

If, as expected, there's a new wave of H1N1 swine flu -- and if it doesn't peak before the vaccine becomes widely available -- demand for the vaccine will be high (as it now is in Australia). But interest may wane if the next wave of the flu pandemic peaks before most people can get the vaccine.

It seems likely that people will need two doses, given three weeks apart, for protection. That means even those at the front of the vaccine-priority line won't be fully protected until late November, four to six weeks after their first shot.

Ongoing clinical trials will soon answer the question of whether one or two doses is needed, and whether the vaccine appears as safe a the seasonal flu vaccines on which it's based.

Meanwhile, states are making plans for widespread vaccination against both seasonal and pandemic flu.