Title :

Case-control vaccine effectiveness studies: Preparation, design, and enrollment of cases and controls.

Abstract :

Case-control studies are commonly used to evaluate effectiveness of licensed
vaccines after deployment in public health programs. Such studies can provide
policy-relevant data on vaccine performance under 'real world' conditions,
contributing to the evidence base to support and sustain introduction of new
vaccines. However, case-control studies do not measure the impact of vaccine
introduction on disease at a population level, and are subject to bias and
confounding, which may lead to inaccurate results that can misinform policy
decisions. In 2012, a group of experts met to review recent experience with
case-control studies evaluating the effectiveness of several vaccines; here we
summarize the recommendations of that group regarding best practices for
planning, design and enrollment of cases and controls. Rigorous planning and
preparation should focus on understanding the study context including
healthcare-seeking and vaccination practices. Case-control vaccine effectiveness 
studies are best carried out soon after vaccine introduction because high
coverage creates strong potential for confounding. Endpoints specific to the
vaccine target are preferable to non-specific clinical syndromes since the
proportion of non-specific outcomes preventable through vaccination may vary over
time and place, leading to potentially confusing results. Controls should be
representative of the source population from which cases arise, and are generally
recruited from the community or health facilities where cases are enrolled.
Matching of controls to cases for potential confounding factors is commonly used,
although should be reserved for a limited number of key variables believed to be 
linked to both vaccination and disease. Case-control vaccine effectiveness
studies can provide information useful to guide policy decisions and vaccine
development, however rigorous preparation and design is essential.

Authors :

Verani, J.R., Baqui, A.H., Broome, C.V., Cherian, T., Cohen, C., Farrar, J.L., Feikin, D.R.,
Groome, M.J., Hajjeh, R.A., Johnson, H.L., Madhi, S.A., Mulholland, K., O'Brien, K.L., Parashar,
U.D., Patel, M.M., Rodrigues, L.C., Santosham, M., Scott, J.A., Smith, P.G., Sommerfelt, H., Tate,
J.E., Victor, J.C., Whitney, C.G., Zaidi, A.K., Zell, E.R.

PubMed link :

Journals :

Vaccine. 2017