President Obama has declared the swine flu outbreak a national emergency. But if you're still waiting to get the swine flu vaccine, looks like you're going to have to wait a bit longer:

Less than half of the swine-flu vaccine expected to be shipped to doctors, hospitals and clinics in the U.S. this month has been shipped so far. The disease now is widespread in 46 states and the U.S. death toll has passed 1,000.

The delays are occurring around the globe, officials said, and are due to a series of manufacturing difficulties, as vaccine makers scramble to fill vast orders using an old technology that requires growing virus in chicken eggs.

It takes about six to nine months to produce vaccine once a flu strain has been identified.

A total of 11.3 million doses of vaccine had been shipped to U.S. doctors, hospitals, and clinics as of Wednesday, according to the federal Centers for Disease Control and Prevention, out of a total of 14.1 million doses that manufacturers had shipped to warehouses by that time.

By Friday, 16.1 million doses of vaccine for what is also called H1N1 flu had been shipped to warehouses, the CDC said.

The total is far below the government's most recent estimate that by the end of this month, about 28 million to 30 million doses would be ready.

That estimate itself is a revision, made last week, from a prior expectation of about 40 million doses by the end of the month. However, the number of doses shipped is steadily increasing.