The U.S. influenza season is starting slowly but it is still too early to tell how severe the outbreak will be as the nation faces a vaccine shortage, the head of the Centers for Disease Control and Prevention (CDC) said on Sunday.

Texas and New York have reported some localized outbreaks, and sporadic cases have turned up in some other states, Dr. Julie Gerberding told reporters at the American Public Health Association’s annual conference. No states yet have widespread activity, and some states have not reported any flu cases.

“We’re not getting off to a fast start,” Gerberding said, adding, “Flu is so unpredictable. I’m not making any predictions.”

Officials are closely watching flu activity as they try to direct remaining vaccine supplies to people most at risk of serious complications from the virus.

The U.S. government had hoped to have 100 million doses available for the current flu season but lost half that supply when maker Chiron Corp. was barred from shipping its vaccine after some doses were found to be contaminated.

The government now expects about 60 million flu shots will be distributed, after rival vaccine makers MedImmune and Aventis-Pasteur, a unit of Sanofi-Aventis, squeezed out some extra doses.

To track the flu’s spread, the CDC is starting to monitor sales of over-the-counter drugs that people with flu may want. A sudden spike in sales of such drugs could signal a flu outbreak.

“We think flu is an example where knowing what nonprescription drugs people are buying at the drugstores may be an earlier indicator than waiting until we see the hospitals fill up with the sickest patients,” Gerberding said.

The government has stockpiled antiviral drugs that could be distributed to treat flu patients or prevent new infections.

Flu kills an estimated 36,000 Americans each year and sends about 200,000 to the hospital.

Officials are looking at ways to avoid future vaccine shortages, including having the government buy millions of doses each year to entice more companies to make the shots. Demand fluctuates from year to year.

Several ideas are under consideration, Gerberding said.

She added that officials were “very concerned” the deadly bird flu in Asia may migrate to the United States and spread quickly.

The U.S. government ordered 2.4 million doses of a bird flu vaccine from Aventis and Chiron. Production is on schedule, Gerberding said. But the vaccine may not help if the flu virus mutates, she added.