As a relief pitcher for the San Francisco Giants, Sergio Romo makes a living striking out batters. Off the field, Romo is trying to strike out whooping cough.

In front of a roomful of cameras on Tuesday, Romo rolled up his sleeves and, for the first time in his life, received a Tdap shot, the vaccine for whooping cough. (The right-hander took the shot in his left arm.)

"You didn't even flinch!" exclaimed Dr. Susan Fernyak of the city's Department of Public Health, who administered the vaccine. "You're so tough."

"I have to be," the 28-year-old Romo replied.

Romo and the Giants are working with the city's Department of Public Health and the San Francisco Immunization Coalition to encourage people to get vaccinated against the disease. A new state law requires all students in grades seven to twelve to be vaccinated with Tdap within the first month of the upcoming school year.

Whooping cough or pertussis is a bacterial infection that killed 10 infants and infected more than 9,000 Californians last year -- the most cases in six decades. So far this year, the California Department of Public Health has reported 2,000 cases and no fatalities.

At Tuesday's news conference, a brother and sister who contracted the disease in December described the coughing fits they battled for months.

“When we would get the coughing attacks, it would just take all the air out of you. Like you wanted to stop, and you just couldn’t breathe anymore,” said Emily Tobita, 18. “Your throat would hurt, your chest would hurt, your stomach would hurt.”

“At the end of a really bad session, I would end up throwing up,” she added.

Neither Emily, nor her twin brother, Zack, had received the Tdap vaccine, which was not required when they were seniors at George Washington High School. The illness kept them out of school for three weeks, but the coughing persisted for three months.

Coughing attacks often lasted up to five minutes, Zack said. "It'd wake you up in the middle of the night all the time. Anytime of the day, it was cough cough cough cough cough. I couldn’t play sports; couldn’t do my daily routine,” he described.

When they were diagnosed, Zack and Emily didn't even know what whooping cough was.

Romo didn't know about the vaccine until the San Francisco Immunization Coalition asked him to take part in their public service campaign last year. Then, he made sure to vaccinate his 5-year-old-son, Rilen. The reliever and his wife are expecting a second son next month.

“The health of my children is my first priority,” Romo said. “It’s just one of those things that if you don’t know about it, or if you don’t tell people about it, it’s going to continue to get bigger and bigger, and we don’t want it to.”

Romo is still getting used to his role as a spokesman.

“I get an opportunity to play in front of thousands of fans," Romo said, but "never have I been as nervous as I am now,” he admitted.

A city-sponsored clinic will provide free Tdap vaccines at 1 - 4 p.m. on Saturday at the French American International School at 151 Oak Street. Tdap shots are also available at pediatric clinics and drugstores.

California is one of 38 states that require middle school and high school students to get the Tdap vaccine. Because the vaccine wanes after about five years, health officials recommend adults and children get booster shots.