CVS Caremark says it is making flu shots available starting Tuesday, which is three or four weeks earlier than usual.

The company said appointments for the flu vaccine will be available at all 500 of its walk-in MinuteClinics, and at scheduled events in many of its 6,900 drugstores. The vaccine is intended to prevent the seasonal flu and is separate from vaccines for swine flu. CVS said a swine flu vaccine could be ready by mid-October.

Dr. Troy Brennan, CVS's Chief Medical Officer, said the seasonal flu shot will be available throughout the fall. The Centers for Disease Control and Prevention recommend the vaccine for children, the elderly, caregivers, pregnant women, and people with weak immune systems or many other chronic health problems.

CVS said it will hold more than 9,000 "flu shot clinic events" at its stores, where pharmacists or other health care workers will give the injections. Those events will start Sept. 15, and a schedule will be available at the Woonsocket, R.I., company's Web site.

Brennan said most of the experts he has spoken to are expecting greater demand for the vaccine this year because of the swine flu pandemic. Several companies are testing swine flu vaccines, which may be administered as one shot or two.

The flu shot contains flu virus particles that are already dead, the CDC says, so it is not possible to get the flu from the vaccine.

According to the agency, about 226,000 Americans are hospitalized with the flu each year, and about 36,000 die.