The flu is sweeping across the nation earlier than normal this year, and the North Shore is not immune.

Health officials nationally are warning of a harsh flu season, which usually peaks in midwinter. The state’s Department of Public Health says the state is one of many reporting above-average flu hospitalization rates.

State public health officials have reported 18 flu-related deaths, and the city of Boston yesterday declared a public health emergency.

“We are seeing lots of it with different variations of symptoms,” said Dr. Phillip Rice, vice chairman of the emergency department at the North Shore Medical Center in Salem. “This is much worse than anything we’ve seen in the last decade.”

Rice said they’ve had to adjust staffing at the hospital to accommodate all the flu-related patients.

“It’s all hands on deck,” he said.

Because the virus mutates every year, it is unknown why the peak season might hit earlier or later in any given year, Rice said.

Officials at Beverly Hospital could not be reached for comment yesterday.

Massachusetts was one of 29 states reporting high levels of “influenza-like illness,” according to the most recent weekly flu advisory issued by the Centers for Disease Control and Prevention.

The estimated rate of flu-related hospitalizations in the U.S. was 8.1 per 100,000 people, which is high for this time of year, according to Dr. Joe Bresee, chief of the epidemiology and prevention branch of the CDC’s influenza division. The agency’s next advisory will be issued tomorrow.

Like many other health officials, Rice recommended people get a flu shot, while cautioning that vaccines will not guarantee people won’t come down with the flu.

Sharon Cameron, Peabody’s director of health and human services, said the city had seen a dramatic increase in the number of confirmed flu cases in that city.

Like many other towns and cities, they have been holding vaccination clinics and spreading prevention awareness since before the flu season.

“We are noticing that people are paying closer attention because of the declaration in Boston (yesterday),” she said.

Cameron said the vaccine is widely available at locations throughout the region, including doctor’s offices, pharmacies and local health departments.

Larry Ramdin, health agent in Salem, said Salem hosts flu clinics every Thursday. Residents and those who work in the city can get free vaccinations if they show an insurance card, he said.

“It has peaked earlier, so there are more cases nationally,” Ramdin said. “It is also considered more virulent, which essentially means it spreads faster.”

He said the vaccines are in good supply, with the availability for the city to get more if needed.

There have been 25 confirmed flu cases in Danvers between Dec. 13 and yesterday, said Peter Mirandi, the town’s director of public health.

There were three confirmed cases between November and December.

“In Danvers, we’ve given out 650 doses of free flu vaccines,” he said. “We still have more doses left.”

The department is continuing to offer the free vaccines, which are made available by appointment, he said.

The CDC said the proportion of people visiting health care providers with flu-like symptoms climbed from 2.8 to 5.6 percent in four weeks.

By contrast, the rate peaked at only 2.2 percent during the relatively mild 2011-2012 flu season.

staying healthy this flu season Get the flu shot. Wash your hands often with soap and water, especially after you cough or sneeze. Try to avoid close contact with people who are exhibiting flu-like symptoms, including a fever of 100 degrees or higher, cough, sore throat, stuffy or runny nose, fatigue, and body aches and chills. Avoid touching your eyes, nose and mouth to prevent germs from spreading. Cover your nose and mouth with a tissue when you sneeze or cough. Source: Beverly Hospital FLU SHOTS AVAILABLE Danvers is offering flu shots on Monday, Wednesday and Thursday at the Senior Center, 50 Stone St., by appointment. Call Director of Public Health Peter Mirandi at 978-777-0001, ext. 3025. Salem holds clinics every Thursday from 5:30 to 6:30 p.m. for residents and people who work in the city. They are held at 120 Washington St. Call 978-741-1800 for more information.

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By Jonathan Phelps