Massachusetts is one state that the CDC had identified as having high activity of influenza-like illness based on the week ending December 29, but downgraded it to "moderate" activity in Friday's update.

Boston Mayor Thomas Menino had declared a public health emergency in the city Wednesday because of the flu.

Since October 1, there have been 700 confirmed influenza cases among Boston residents, according to Menino's office; that's 10 times more than were seen in all of last year's flu season.

There have been 18 flu-related deaths this season in Massachusetts, CNN affiliate WCVB reported. Hospitalization rates are higher than in the last two years, Kevin Cranston of the state's Bureau of Infectious Diseases told WCVB. Most deaths have been in older patients, he said.

Menino is collaborating with the Boston Public Health Commission and community health centers to offer free vaccination clinics this weekend. The mayor urged residents to stay home from work or school if they are sick, and to get flu shots.

"This is the worst flu season we've seen since 2009, and people should take the threat of flu seriously," Menino said in a statement. More than 4% of emergency department visits at Boston hospitals are from flu cases, up from 1% during non-flu season.

Massachusetts General Hospital has already counted 532 cases of flu among patients, which is more than the Boston hospital saw in any of the previous three flu seasons, spokeswoman Kristen Stanton said Wednesday.

Signs posted throughout the hospital discourage anyone from visiting who has a cough or fever, she said, and anyone who does visit with those symptoms must wear a mask and perform hand hygiene. All staff must wear a mask when caring for possible flu patients, and staff members who have not been vaccinated must wear a mask while caring for any patient.

As an extra precaution amid flu fears, Bishop Robert P. Deeley of Boston sent a note to all pastors in the Boston Archdiocese suggesting that during the Sign of Peace, "the faithful, instead of a handshake, may bow to the persons nearby." Similarly, in Washington, a note from the Archdiocese's communications office says that parishioners don't have to shake hands or receive communion from the chalice.

"Those who are sick may wish to watch the Sunday TV Mass on their television at home and pray in solidarity with their parish community," the statement said.

Deaths in other states

The CDC only tracks pediatric flu-related deaths, but some individual states release reports of influenza deaths among adults.

The Oklahoma Department of Health said Thursday the state has had eight influenza-linked deaths since September 30, while the Minnesota Department of Health has recorded 27 flu-related deaths.

"We are clearly at a high level of influenza activity in the state," Minnesota Health Commissioner Dr. Edward Ehlinger said in a statement. "But it's important to keep this year in perspective: What is occurring has happened before."

The number of flu-related deaths elsewhere, according to state health officials:

-- Pennsylvania has had 22 deaths. Most of the deaths were among people older than 65.

-- Indiana has 13 confirmed adult deaths and two pediatric deaths.

-- Arkansas has seven confirmed flu fatalities.

-- South Carolina has counted 22 deaths.

-- In Illinois, there have been six deaths.

-- In Michigan, there have been four pediatric deaths.

Type of flu

The type of flu that is going around is called H3N2, which is often linked to more serious disease, compared with some other flu varieties, Fauci said.

That type of flu matches up well to the vaccine that is being distributed and given out throughout the United States.

People may get more complications from this particular strain of H3N2, "which may make them ill for a longer period of time," Dr. Michael Jhung, medical epidemiologist in the influenza division at the CDC, told CNN's Mary Snow.