Officials say the delays are occurring around the globe, 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 usually takes about six to nine months to produce vaccine once a flu strain has been identified.
The total amount of vaccine that has been shipped 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. However, the number of doses shipped is steadily increasing.
"We are nowhere near where we thought we'd be by now," CDC Director Thomas Frieden said Friday. "We share the frustration of people who have waited in line or called a number or checked a Web site and haven't been able to find a place to get vaccinated."
He declined to provide specific projections for delivery of more doses but said he expected the supply to be "much more widespread" within the next several weeks. "We have confidence that ultimately there will be enough vaccine for everybody who wants to be vaccinated to get vaccinated," he said.
The U.S. government has invested more than $2 billion to develop newer, faster methods of vaccine production, but these aren't yet ready for response to a pandemic. The delays raise questions as to how well the vaccine supply will be able to stem the current wave of infection.
The process has been slower than usually seen with seasonal vaccines. Viruses for both vaccines go through a purification process after being grown in eggs.
One problem is that Glaxo, which has contracted to provide 7.6 million doses of vaccine to the U.S., has yet to get Food and Drug Administration approval for its vaccine. A Glaxo spokeswoman said she couldn't speculate on the timing of approval. The FDA declined to comment.
Some suppliers have also experienced "brief interruptions in operations" of new production lines started up to handle the huge demand.