The H1N1 flu vaccine is becoming more available, but it is still being outpaced by the virus itself, the head of the U.S. Centers for Disease Control and Prevention said Tuesday.

“Essentially what we’re seeing is that the virus continues to be spreading across the country and we are seeing a steady increase in the availability of the vaccine, but not as quickly as we’d like it to be,” CDC Director Thomas Frieden said during an afternoon press briefing.

The government has received 31.8 million doses of H1N1 vaccine and expects to receive several million more by the end of the week, Frieden said.

Pennsylvania last week had to discard 6,000 doses of H1N1 vaccine because it was not properly refrigerated. With the U.S. already facing a shortage, Frieden said every dose is important, but that relatively few mishaps have occurred since the vaccine became available.

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“It’s obviously frustrating and we regret when any loss of vaccine occurs, but we’ve shipped out 30 million doses and only a few incidences of improper handling have occurred,” he said. “This is why it’s important that proper tracking and monitoring of the vaccine are done, and why we can’t rapidly send out dosages, because not every provider has a refrigerator that can monitor the temperature of the vaccine properly.”

At least 114 children have died from H1N1 flu complications since the spring, the CDC said last week. The government has released more Tamiflu for children to remedy spot shortages of the children's version of the flu medication. Tamiflu has been shown to reduce the severity of flu symptoms if used within 72 hours of coming down with the virus.

Frieden said virtually all of the flu spreading throughout the U.S. at this time is H1N1.

“There’s almost no seasonal flu so far,” he said. “We’ve seen a few strains here and there, but overwhelmingly H1N1 is the strain circulating and it continues to be very tightly matched with vaccine.”

Frieden says there has been an unprecedented demand for the seasonal flu vaccine this year -- the CDC expects as many as 114 million Americans to get vaccinated -- and the government has already shipped 90 million doses.

More than 1,000 Americans have died from H1N1 since it was first diagnosed in April. About 36,000 Americans, most of them elderly or people with underlying health conditions, die each year from seasonal flu.

Frieden said people in high risk groups, especially those with asthma, should seek immediate medical attention if they experience flu-like symptoms.

“We know that the majority of hospitalizations from H1N1 are in people with asthma and we also know that half of people with asthma who get H1N1 do not seek medical attention,” Frieden said, referring to a telephone survey conducted by the CDC in which 50 percent of asthmatics said they did not seek medical attention for flu-like symptoms.

Frieden said the majority of hospitalizations continue to involve children and people under the age of 25. He added that though the elderly are less likely to get H1N1 than younger adults and children, the virus can be as deadly to them if they do come down with it.