Alexander 2004.
| Methods |
Study design: interrupted time series, uncontrolled before‐and‐after. National surveillance data from 1990 to 2003 for cases of confirmed paralytic poliomyelitis. The Centers for Disease Control and Prevention (CDC) has maintained national poliomyelitis surveillance since 1955. This system relies on voluntary reporting of suspected cases from healthcare providers and laboratories through local and state health departments to the CDC, the Vaccine Adverse Events Reporting System, and the National Vaccine Injury Compensation Program. Although laboratory technology evolved during the study period, polioviruses were isolated and identified using conventional procedures of inoculation of processed specimens onto susceptible cell cultures. Isolates were then determined to be vaccine‐related by 1 of several standard molecular methods Setting: USA Study dates: 1990 to 2003 |
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| Participants | Age: range = 19 to 35 months | |
| Interventions | To reduce the VAPP burden, national vaccination policy changed in 1997 from reliance on OPV to options for a sequential schedule of inactivated poliovirus vaccine (IPV) followed by OPV. In 2000, an exclusive IPV schedule was adopted. Before: exclusive use of OPV scheme OOOO (OPV at 2, 4, 12 to 18 months and again at 4 to 6 years) between 1990 and 1996 After: sequential scheme IIOO (IPV at 2 and 4 months of age followed by OP\/ at 12 to 18 months and again at 4 to 6 years) between 1997 and 1999. 13 cases of VAPP occurred, none of them in persons who had followed the sequential IPV‐OPV or all‐IPV schedules. |
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| Outcomes |
*The sources were national information systems. Timing of outcome assessment: before, during, and after implementation of policy changes Follow‐up: 3 years |
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| Notes | The last case of poliomyelitis in the USA due to indigenously acquired wild poliovirus occurred in 1979; however, as a consequence of oral poliovirus vaccine (OPV) use that began in 1961, an average of 9 cases of vaccine‐associated paralytic poliomyelitis (VAPP) were confirmed each year between 1961 and 1989. | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| ITS: protection against secular changes | Low risk | Comment: the intervention appears to occur independently of other changes over time for VAPP cases. |
| ITS: data were analysed appropriately | Unclear risk | Comment: data were presented but not analysed as ITS, therefore, we re‐analysed the data. |
| ITS: reason given for the number of points pre‐ and post‐intervention | Low risk | Comment: the rationale for the yearly points is justified in the context of national poliomyelitis surveillance. |
| ITS: shape of the intervention effect was specified | Low risk | Comment: data were analysed as an ITS but were re‐analysed as time series regression models were used to analyse the data |
| ITS/UBA: blinded assessment of primary outcome(s) | Low risk | Comment: outcome variable is objective (case of paralytic poliomyelitis). |
| ITS/UBA: reliable primary outcome measure(s) | Low risk | Comment: Centers for Disease Control and Prevention has maintained national poliomyelitis surveillance since 1955. |
| ITS: intervention unlikely to affect data collection | Low risk | Comment: sources and methods of data collection were the same before and after the intervention. The outcome variable is objective (case of paralytic poliomyelitis). |
| ITS: completeness of data set | Low risk | Comment: data set probably covers 80% to 100% of total number of episodes in study |
| UBA: follow‐up of professionals | Low risk | Comment: low risk of bias in the context of a proper national poliomyelitis surveillance |
| UBA: follow‐up of patients | Low risk | Comment: low risk of bias in the context of a proper national poliomyelitis surveillance |
| Conflict of interest | Low risk | Comment: not clearly stated. Probably internal support from study authors' affiliation institution: National Immunization Program and National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia |