Which major change in polio immunization policy occurred by 2000?

• A. Move to OPV-only schedule
• B. IPV-only schedule started earlier
• C. No changes
• D. Transition to an all-IPV schedule

Answer: (D)

A major policy move was shifting from the oral live polio vaccine to an inactivated injectable vaccine, aiming for an all-IPV routine schedule. This change grew out of safety concerns with OPV, since the live vaccine can very rarely cause vaccine-associated paralytic polio and, in areas with imperfect immunity, can give rise to circulating vaccine-derived poliovirus. IPV, made from inactivated virus, cannot cause disease or VAPP, so adopting IPV-only reduces these risks while still protecting children from polio. By around 2000, many programs—notably in polio-free regions like the United States—had moved toward an all-IPV schedule, marking a major shift in how polio prevention was delivered.