Health officials are reminding parents that children under 10 who have been vaccinated for swine flu will need a booster shot, even if that means standing in line a second time. A second dose of the H1N1 vaccine is recommended for children because they have less-developed immune systems than adults. While the first dose offers a beginning dose of immunity, a booster will more fully protect young children. The booster shot should be given 28 days or later after the first dose. Students at Newcastle Elementary School were among the first in the state to be immunized last month and are due for booster shots. McClain County Health Department nurses administered initial doses at the school, but students should get the booster at an immunization site or doctor’s office, administrator Sheri Kenney said. H1N1 vaccinations were offered on a walk-in basis Wednesday at county health department buildings in Purcell and Blanchard, Kenney said. She said lines were short and more walk-in clinics are being scheduled. Health officials said one dose of the vaccine for children under age 10 provides 30 to 60 percent immunity, but a second dose can bring immunity to 80 to 90 percent, equal to what adults achieve with one dose. No vaccines are 100 percent effective. Linda Thompson, an immunobiologist with the Oklahoma Medical Research Foundation, said adults may have some immunity to H1N1 because they’ve been exposed to similar viruses over the years, but small children have no protection. The Oklahoma City-County Health Department will give H1N1 shots and nasal spray free to the public from 10 a.m. to 3 p.m. Saturday at John Marshall High School, 12201 N Portland Ave. The shots will be offered to pregnant women, children 6 months to 18 years old, custodial parents of infants younger than 6 months old, adults age 18 to 64 with chronic disease and health care workers.