With more than 23 million doses of swine flu vaccine now available, health officials are visiting vaccine plants to check for any more pending interruptions to what appears to be a slowly but steadily growing supply.

About 9 million doses trickled onto the market in the past week alone, and Health and Human Services Secretary Kathleen Sebelius said Wednesday that site visits and other checks suggest production problems "have in large part been fixed."

"We are checking and double-checking," she said, acknowledging how the limited supply makes it difficult for people to get vaccinated.

For about six weeks, the government repeatedly said there would be about 45 million doses of swine flu vaccine ready by mid-October, down from an initial early summer prediction of 120 million doses. Only around Columbus Day did officials get word from vaccine manufacturers that delays were worse than the companies had acknowledged - and long lines for scarce supplies persist around the country.

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The lesson from sharing what Sebelius called the earlier "pretty rosy scenarios": Be cautious about setting overly high expectations for the coming weeks. So while officials hope to be back on track in November, Sebelius offered no specific dose predictions Wednesday.

Anyone who stood in line unsuccessfully should "come back," she urged.

Although the new flu that scientists call the 2009 H1N1 strain is surging, there's no way to know when it will peak - and there could be another wave of illness after the first of the year or in the spring, she said.

The United States has ordered 250 million doses of swine flu vaccine. Some 25 million have been promised to developing countries, but Sebelius said the decision on when to begin that sharing won't be made until more supplies arrive to protect Americans.

Also Wednesday, the World Health Organization plans to distribute 200 million doses of swine flu vaccine to 100 developing countries.

WHO Secretary-General Margaret Chan says shipments could begin next month.

The WHO says nearly 5,000 swine flu deaths have been reported worldwide.