Campaigns with oral polio vaccine may lower mortality and create unexpected results

Abstract

Three studies from Guinea-Bissau found conflicting effects of OPV-at-birth (OPV0) on child survival. One study from 2004 suggested excess male mortality among children receiving OPV0 compared with children receiving NoOPV0 during a period of shortage of OPV. However, two subsequent studies showed beneficial effects of OPV0. In 2004, two national OPV-campaigns had been conducted in Guinea-Bissau. In a reanalysis of the 2004-study, in a survival analysis the age-adjusted mortality rate of study participants was 67% (95% CI = 42–81%) lower after the OPV-campaigns than before the campaigns. In the OPV0 group only 22% (655/3031 person-years (pyrs)) of follow-up time was “after” the OPV-campaigns whereas 55% (473/859 pyrs) of the time in the NoOPV0 group was post-campaign (p < 0.0001, Chi2). Censoring for OPV-campaigns in the original study removed excess male mortality and made the three studies more homogeneous. Overall, there is now considerable evidence that OPV, like other live vaccines, has important beneficial non-specific effects.

National Immunization Campaigns with Oral Polio Vaccine Reduce All-Cause Mortality: A Natural Experiment within Seven Randomized Trials

“…The effect of OPV-only campaigns appeared to be slightly stronger for boys than for girls, though the difference was not statistically significant. Other studies of OPV have also suggested a stronger beneficial effect for boys ( 16 , 26 ).…”

“…One observational study has suggested that routine OPV0 compared with NoOPV0 might have a negative effect for boys but not for girls ( 33 ). However, the boys who had “benefited” from not having received OPV0 had been more likely to receive campaign OPV than the boys receiving OPV0 and this is likely to have been the real cause of their lower mortality ( 26 ). In the subsequent RCT to measure the effect, OPV0 was significantly beneficial, particularly for boys ( 16 ).…”

“…There has been little research in why NSEs often differ by sex. Several studies have found a stronger beneficial effect of OPV for males than for females ( 16 , 26 ). Other live vaccines, such as MV ( 1 , 13 , 27 ) may have a stronger beneficial effect for females.…”

How to evaluate potential non-specific effects of vaccines: the quest for randomized trials or time for triangulation?

“…Second, several studies have shown OPV-campaigns to be associated with a marked decline in the general mortality rate [45][46][47]. Third, OPV campaigns have modified estimated mortality outcomes in studies of other vaccines [45,48].…”

“…Seventh, most studies suggest the OPV has a stronger beneficial effect for boys than for girls [44][45][46].…”