Scores of grumbling parents facing a threat of jail lined up at a courthouse Saturday to either prove that their school-age kids already had their required vaccinations or see that the youngsters submitted to the needle. The get-tough policy in the Washington suburbs of Prince George's County was one of the strongest efforts made by any U.S. school system to ensure its youngsters receive their required immunizations. Two months into the school year, school officials realized that more than 2,000 students in the county still didn't have the vaccinations they were supposed to have before attending class. So Circuit Court Judge C. Philip Nichols ordered parents in a letter to appear at the courthouse Saturday and either get their children vaccinated on the spot or risk up to 10 days in jail. They could also provide proof of vaccination or an explanation why their kids didn't have them. It was very heavy handed," [school mom Aloma Martin] said of the county's action. "From that letter, it sounded like they were going to start putting us in jail." Any children who still lack immunizations could be expelled. Their parents could then be brought up on truancy charges, which can result in a 10-day jail sentence for a first offense and 30 days for a second. Maryland, like all states, requires children to be immunized against several childhood illnesses including polio, mumps and measles. In recent years, it also has required that students up to high school age be vaccinated against hepatitis B and chicken pox. Several organizations opposed to mass vaccinations demonstrated outside the courthouse. While the medical consensus is that vaccines are safe and effective, some people blame immunizations for a rise in autism and other medical problems. "People should have a choice" in getting their children immunized, said Charles Frohman, representing a physicians' group opposed to vaccines.