Health officials from the U.S. Centers for Disease Control and Prevention said Thursday that the H1N1 virus is still circulating, and although activity has decreased, Americans cannot afford to become complacent.

"We want more people to get the vaccine," said Dr. Anne Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases. "There are 136 million doses available; we have an ample supply in most of the country. Most states have opened up the vaccine to anyone who wants it."

Schuchat said there is still widespread H1N1 flu activity in four states: Delaware, Maine, New Jersey and Virginia.

"We still have more activity than usual, but we’re certainly below where we were weeks ago," she added. "And we haven’t seen an emergence of seasonal flu... although we’ve seen an uptick in pneumonia in influenza deaths last week. That isn’t something we usually see during the Christmas holiday."

The H1N1 virus sickened more than 50 million Americans and killed 10,000 in the first seven months of the pandemic.

Schuchat pointed to late 1957, a time when health officials gave the public the all-clear after a heavy flu season, but then saw an increase in the coming weeks.

Schuchat said right now experts do not think H1N1 activity will increase, but it’s in everyone’s best interest to receive the vaccine.

"I wish I could tell you when this particular strain will stop circulating, but I can't," Schuchat said.

Sunday marks the start of National Influenza Vaccination Week.