Table II.

Calibration of the PIR of OPV and OPV-Related Viruses to the Observed VAPP Incidence After WPV Elimination and Before the Switch to the Sequential eIPV-tOPV Schedule in the USA (from CDC, unpublished data; excluding immunodeficient VAPP and assuming 96% completeness of reporting)^(44,50)

VAPP cases, 1980–1996	Type 1	Type 2	Type 3
Estimated actual VAPP casesa
- recipient VAPP	2.4	19.2	43.2
- nonrecipient VAPP	4.7	20.4	28.2
VAPP cases estimated by the USA model
- recipient VAPPb	2.5	20.0	46.1
- nonrecipient VAPPc	6.0	26.9	25.5

Acronyms: CDC = (U.S.) Centers for Disease Control and Prevention; eIPV = enhanced-potency inactivated poliovirus vaccine; OPV = oral poliovirus vaccine; PIR = paralysis-to-infection ratio; tOPV = trivalent OPV; USA = United States of America; VAPP = vaccine-associated paralytic poliomyelitis; WPV = wild poliovirus

^aNumbers by serotype reflect relative frequency of each serotype isolated from VAPP cases with a single isolated serotype, multiplied by total estimated VAPP cases in the same category (i.e., recipient or nonrecipient).

^bRecipient VAPP incidence calibrated to match the estimated actual incidence by setting the PIR for OPV (PIR₀; see Table I) equal to the estimated actual incidence divided by the total number of paralytic infections in OPV recipients in the model (small differences due to rounding of the PIR for OPV).

^cNonrecipient VAPP incidence calibrated by finding the approximate shape parameter (z_pir; see Table 1) that best matches the estimated actual nonrecipient VAPP cases for each serotype.