Some hospitals have achieved 90 percent but many fall short. A government health advisory panel has urged those below 90 percent to consider a mandatory program.
Also, the accreditation body over hospitals requires them to offer flu vaccines to workers, and those failing to do that and improve vaccination rates could lose accreditation.
Starting this year, the government's Centers for Medicare & Medicaid Services is requiring hospitals to report employees' flu vaccination rates as a means to boost the rates, the CDC's Bridges said. Eventually the data will be posted on the agency's "Hospital Compare" website.
Several leading doctor groups support mandatory flu shots for workers. And the American Medical Association in November endorsed mandatory shots for those with direct patient contact in nursing homes; elderly patients are particularly vulnerable to flu-related complications. The American Nurses Association supports mandates if they're adopted at the state level and affect all hospitals, but also says exceptions should be allowed for medical or religious reasons.
Mandates for vaccinating health care workers against other diseases, including measles, mumps and hepatitis, are widely accepted. But some workers have less faith that flu shots work — partly because there are several types of flu virus that often differ each season and manufacturers must reformulate vaccines to try and match the circulating strains.
While not 100 percent effective, this year's vaccine is a good match, the CDC's Bridges said.
Several states have laws or regulations requiring flu vaccination for health care workers but only three — Arkansas, Maine and Rhode Island — spell out penalties for those who refuse, according to Alexandra Stewart, a George Washington University expert in immunization policy and co-author of a study appearing this month in the journal Vaccine.
Rhode Island's regulation, enacted in December, may be the toughest and is being challenged in court by a health workers union. The rule allows exemptions for religious or medical reasons, but requires unvaccinated workers in contact with patients to wear face masks during flu season. Employees who refuse the masks can be fined $100 and may face a complaint or reprimand for unprofessional conduct that could result in losing their professional license.
Some Rhode Island hospitals post signs announcing that workers wearing masks have not received flu shots. Opponents say the masks violate their health privacy.
"We really strongly support the goal of increasing vaccination rates among health care workers and among the population as a whole," but it should be voluntary, said SEIU Healthcare Employees Union spokesman Chas Walker.
Supporters of health care worker mandates note that to protect public health, courts have endorsed forced vaccination laws affecting the general population during disease outbreaks, and have upheld vaccination requirements for schoolchildren.
Cases involving flu vaccine mandates for health workers have had less success. A 2009 New York state regulation mandating health care worker vaccinations for swine flu and seasonal flu was challenged in court but was later rescinded because of a vaccine shortage. And labor unions have challenged individual hospital mandates enacted without collective bargaining; an appeals court upheld that argument in 2007 in a widely cited case involving Virginia Mason Hospital in Seattle.
Calhoun, the Illinois nurse, says she is unsure of her options.
"Most of the hospitals in my area are all implementing these policies," she said. "This conflict could end the career I have dedicated myself to."
R.I. union lawsuit against mandatory vaccines: http://www.seiu1199ne.org/files/2013/01/FluLawsuitRI.pdf
AP Medical Writer Lindsey Tanner can be reached at http://www.twitter.com/LindseyTanner