LOS ANGELES — The odds of a third wave of pandemic H1N1 influenza hitting this spring seem to be declining, but authorities are concerned that the virus is still spreading — albeit at a reduced rate from its peak — and is not disappearing as would be expected in a normal influenza outbreak, federal officials said Friday.

“I think the most likely scenario now … is ongoing transmission of the virus, which continues to circulate,” said Dr. Anne Schuchat, director of the Centers for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases. “It is impossible for me to say whether we will have a very large peak in disease, but we also don’t seem to be seeing a disappearance of this disease,” she said.

“My sense is that we are not at all out of the woods because the virus continues to circulate. The chances of a larger wave are difficult to predict, but they may be less likely than continuing circulation of the virus.”

Her thoughts seem to mirror those of the American public. A new poll from the Harvard School of Public Health shows that only 18 percent of Americans think it is “very likely” that there will be a third wave of swine flu.

Still, with continued circulation, “vaccination remains a good idea,” Schuchat said.

For the third week in a row, flu activity has remained below normal levels for this time of year, with no states reporting widespread activity. Also for the third week, visits to physicians’ offices for influenzalike illnesses have remained low. Such illnesses accounted for 1.9 percent of all visits to doctors’ offices in the week ending Jan. 30, well below the 2.3 percent level that authorities consider indicative of an epidemic.

The most concerning statistic is that deaths from pneumonia and influenza have remained above normal for the third consecutive week, particularly among the elderly. This may mean that the virus is finally beginning to make its way into the elderly population, which is most susceptible to adverse effects, but which seemed to have some degree of immunity to the virus.

Testing so far, however, has not been able to show whether the deaths are attributable to swine flu or to other viruses that also circulate at this time of year.

Another nine pediatric deaths associated with flu were reported during the week, bringing the total of laboratory confirmed deaths of children to 321. Some of those deaths occurred earlier in the season, however. Officials believe that more than 1,000 children have so far died from influenza since the pandemic began last April.

About 155 million doses of vaccine are now available, she said, 124 million doses have been shipped, and an estimated 70 million people have been vaccinated, about 23.4 percent of Americans. Because some people have received two doses, a total of 76 million doses have been administered.