Officials on Thursday urged people to get their flu shot this year. Last year's flu was mild but experts say that flu is unpredictable and everybody needs to get their flu shot. 

"I urge everyone to join me and get a flu vaccine this year," said Dr. Howard K. Koh, Assistant Secretary for Health at the U.S. Department of Health and Human Services. Koh got his flu vaccine during the news conference.

About 42 percent of Americans, aged 6 months or older, are estimated to get their flu vaccines during the 2011-2012 flu season. Children, aged 6 months to 23 months, have the highest rates of vaccinations with over 75 percent while for adolescents, the rate of vaccination is just 34 percent.

Approximately 85 million vaccine doses have already been distributed while an expected 135 million doses of vaccination will be available by the end of season.

"The past three years have demonstrated that influenza is predictably unpredictable. When it comes to flu, we can't look to the past to predict the future. Stay healthy -- get vaccinated!" Dr. Koh said.

Influenza and pregnant women

Experts at the news conference urged all pregnant women to get vaccinated against the flu. According to data released at the news conference, about 47 percent of pregnant women had received the flu vaccine last year, a rate that has remained consistent over the years.

"Influenza is five times more likely to cause severe illness in pregnant women than women who are not pregnant," said Laura Riley, MD, director of Obstetrics and Gynecology Infectious Disease, Massachusetts General Hospital. "The flu vaccine is safe and offers protection for the mother. Research shows it can decrease the baby's risk of getting the flu for up to six months after birth," Riley who was representing American College of Obstetricians and Gynecologists (ACOG) said in a press release.

Vaccination remains the first line of defense against influenza, the Centers for Disease Control and Prevention said in the news conference, along with good personal hygiene and appropriate use of drugs against flu for those who get infected.