By 2000, what major change occurred in polio vaccination strategy?

• A. Availability of OPV substantially increased
• B. Shortage of IPV led to all-OPV
• C. No changes to polio vaccine practice
• D. Availability of OPV was substantially diminished, transitioning to an all-IPV schedule

Answer: (D)

The main idea is that polio vaccination strategy shifted from relying on the live oral vaccine to using the injected inactivated vaccine in routine programs. By 2000, many countries had moved to an all-IPV schedule, which reduced dependence on OPV. This change happened because OPV, while cheap and easy to administer and capable of providing good mucosal immunity, carries a small risk of vaccine-associated paralytic polio and, in under-immunized populations, can give rise to circulating vaccine-derived polioviruses. Switching to IPV keeps individuals protected without introducing the live virus into communities, aligning with global eradication goals. In practice, this meant diminished routine availability of OPV as countries adopted all-IPV, even though OPV might still be used in outbreak responses.