In a study that looked at 20 years of data, Public Health Ontario found a 71 per cent drop in doctor’s office and emergency room visits and a 59 per cent decrease in hospitalizations due to chickenpox among children under 18 after the public immunization program was introduced in 2004, compared with two earlier periods. Those time frames captured in the study were 1992 to 1998, when there was no vaccine, and 1999 to 2003, when the shot was available but had to be paid for out of parents’ pockets.