Despite long lines and limited supplies of theH1N1 flu vaccine, U.S. efforts against the disease are not too late, Health and Human Services Secretary Kathleen Sebelius said on Monday.

Sebelius acknowledged frustrating waits to get the vaccine, but said some 16.5 million doses are now being made available, with efforts to get more.

I never like to see people inconvenienced, Sebelius said on ABC's Good Morning America. If we had found the virus a little earlier, we could have started a little earlier.

Asked whether this effort might be too late in light of one estimate that the H1N1 flu virus will peak by October 31, Sebelius said, I don't think it's too late ... What we saw in 1950s (flu pandemic) was that there was a big outbreak in fall and then a new wave in the spring.

With a future wave of H1N1 possible, vaccination is still useful, Sebelius said.

She acknowledged that four out of five sources of the vaccine are outside the United States, but said an additional U.S. plant will be making the vaccine in 2010.

Certainly it's a concern that we rely on other nations to purchase the vaccine, Sebelius said.

In response to a question about whether the United States should have taken more aggressive measures earlier, Sebelius told NBC's Today program that it was unclear early on just how deadly this virus would be.

She noted that 1,000 people have died from this disease in the United States but added, This is not presenting in most people to be a seriously lethal disease.

Anne Schuchat of the U.S. Centers for Disease Control, speaking on CNN, advised healthy adults over 25 and senior citizens to wait and allow more vulnerable patients -- children, young adults, healthcare workers, pregnant women, adults with chronic conditions and parents and others who take care of infants -- to receive the vaccine first.

President Barack Obama has declared 2009 H1N1 swine flu a national emergency which the White House said will make it easier for U.S. medical facilities to handle a surge in flu patients by allowing the waiver of some requirements of Medicare, Medicaid and other federal health insurance programs as needed.