title: Selection and quantification of infection endpoints for trials of vaccines against intestinal helminths.
abstract: Vaccines against human helminths are being developed but the choice of optimal parasitological endpoints and effect measures to assess their efficacy has received little attention. Assuming negative binomial distributions for the parasite counts, we rank the statistical power of three measures of efficacy: ratio of mean parasite intensity at the end of the trial, the odds ratio of infection at the end of the trial, and the rate ratio of incidence of infection during the trial. We also use a modelling approach to estimate the likely impact of trial interventions on the force of infection, and hence statistical power. We conclude that (1) final mean parasite intensity is a suitable endpoint for later phase vaccine trials, and (2) mass effects of trial interventions are unlikely to appreciably reduce the force of infection in the community - and hence statistical power - unless there is a combination of high vaccine efficacy and a large proportion of the population enrolled.
authors: London School of Hygiene and Tropical Medicine, London, UK. neal.alexander@lshtm.ac.uk
authors: Neal
authors: N
authors: Alexander
authors: Bonnie
authors: B
authors: Cundill
authors: Lorenzo
authors: L
authors: Sabatelli
authors: Jeffrey M
authors: JM
authors: Bethony
authors: David
authors: D
authors: Diemert
authors: Peter
authors: P
authors: Hotez
authors: Peter G
authors: PG
authors: Smith
authors: Laura C
authors: LC
authors: Rodrigues
authors: Simon
authors: S
authors: Brooker
mesh_terms: D000818:Animals; D016010:Binomial Distribution; D005243:Feces / Q000469:parasitology; D006373:Helminthiasis / Q000276:immunology / Q000469:parasitology / Q000517:prevention & control*; D006801:Humans; D007411:Intestinal Diseases, Parasitic / Q000276:immunology / Q000517:prevention & control*; D015233:Models, Statistical; D016017:Odds Ratio; D010270:Parasite Egg Count; D016032:Randomized Controlled Trials as Topic; D014611:Vaccination; D014612:Vaccines / Q000276:immunology*
chemical_list: D014612:Vaccines