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Dynamics affecting the risk of silent circulation when oral polio vaccination is stopped.

ABSTRACT: Waning immunity could allow transmission of polioviruses without causing poliomyelitis by promoting silent circulation (SC). Undetected SC when oral polio vaccine (OPV) use is stopped could cause difficult to control epidemics. Little is known about waning. To develop theory about what generates SC, we modeled a range of waning patterns. We varied both OPV and wild polio virus (WPV) transmissibility, the time from beginning vaccination to reaching low polio levels, and the infection to paralysis ratio (IPR). There was longer SC when waning continued over time rather than stopping after a few years, when WPV transmissibility was higher or OPV transmissibility was lower, and when the IPR was higher. These interacted in a way that makes recent emergence of prolonged SC a possibility. As the time to reach low infection levels increased, vaccine rates needed to eliminate polio increased and a threshold was passed where prolonged low-level SC emerged. These phenomena were caused by increased contributions to the force of infection from reinfections. The resulting SC occurs at low levels that would be difficult to detect using environmental surveillance. For all waning patterns, modest levels of vaccination of adults shortened SC. Previous modeling studies may have missed these phenomena because (1) they used models with no or very short duration waning and (2) they fit models to paralytic polio case counts. Our analyses show that polio case counts cannot predict SC because nearly identical polio case count patterns can be generated by a range of waning patterns that generate different patterns of SC. We conclude that the possibility of prolonged SC is real but unquantified, that vaccinating modest fractions of adults could reduce SC risk, and that joint analysis of acute flaccid paralysis and environmental surveillance data can help assess SC risks and ensure low risks before stopping OPV.

SUBMITTER: Koopman JS

PROVIDER: S-EPMC5608688 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature

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Dynamics affecting the risk of silent circulation when oral polio vaccination is stopped.

Koopman J S JS Henry C J CJ Park J H JH Eisenberg M C MC Ionides E L EL Eisenberg J N JN

Epidemics 20170301

Waning immunity could allow transmission of polioviruses without causing poliomyelitis by promoting silent circulation (SC). Undetected SC when oral polio vaccine (OPV) use is stopped could cause difficult to control epidemics. Little is known about waning. To develop theory about what generates SC, we modeled a range of waning patterns. We varied both OPV and wild polio virus (WPV) transmissibility, the time from beginning vaccination to reaching low polio levels, and the infection to paralysis ...[more]

PMID: 28283373

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Project description:BACKGROUND:Children who receive all doses of scheduled vaccines reduce their susceptibility to vaccine-preventable diseases. In India, full immunization coverage has increased significantly. However, only a small proportion of children are immunized on time. Globally, studies on factors affecting coverage of childhood immunization have found a significant impact by demand and supply-side determinants. This paper explores the demand-side determinants of timely immunization of the third dose of oral polio vaccine (OPV3) among children aged 6-11 months in the catchment areas of CORE Group Polio Project India. METHODS:We analyzed secondary de-identified data from a household level 'Doers and Non-doers survey' conducted in 2015. Determinants of timely OPV3 immunization were identified by modeling the characteristics of index children and survey respondents, surveyed households, respondents' media habits, their exposure to immunization services and perceptions towards child immunization, through a multinomial regression analysis. RESULTS:The eight demand-side predictors based on the background characteristics and perceptions of caregivers determined timely vaccination of OPV3. The strongest predictor of timely OPV3 immunization was found to be the fathers' educational level. Children of uneducated or lesser educated fathers had increased odds of not receiving the OPV1 vaccination, as compared to children of more educated fathers (OR > 10). Respondents who strongly perceived other (non-health) benefits of child immunization were three times more likely to timely vaccinate their children than those who do not. Furthermore, mothers who disagreed with the positive attributes of child immunization were 25 times more likely to delay or not to take their children for OPV immunization on time. CONCLUSIONS:This study found eight essential factors that are responsible for timely OPV3. Despite limitations in data collection and analysis, immunization programs in India could use the eight identified demand-side determinants of timeliness and tailor communication strategies accordingly. We suggest that program communication efforts be directed at male community members; such messaging should address parents' perceptions of non-health benefits and stress the positive attributes of child immunization. Further investigation would be helpful to assess the various risk factors of under-vaccination as well as vaccinators' understating about timely immunization.

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Dynamics affecting the risk of silent circulation when oral polio vaccination is stopped.

Publications

Dynamics affecting the risk of silent circulation when oral polio vaccination is stopped.

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