Assessing the risk of measles resurgence in a highly vaccinated population: Belgium anno 2013

Background Mathematical modelling of infectious disease is increasingly used to help guide public health policy. As directly transmitted infections, such as influenza and tuberculosis, require contact between individuals, knowledge about contact patterns is a necessary pre-requisite of accurate model predictions. Of particular interest is the potential impact of school closure as a means of controlling pandemic influenza (and potentially other pathogens). Methods This paper uses a population-based prospective survey of mixing patterns in eight European countries to study the relative change in the basic reproduction number (R0 - the average number of secondary cases from a typical primary case in a fully susceptible population) on weekdays versus weekends and during regular versus holiday periods. The relative change in R0 during holiday periods and weekends gives an indication of the impact collective school closures (and prophylactic absenteeism) may have during a pandemic. Results Social contact patterns differ substantially when comparing weekdays to the weekend and regular to holiday periods mainly due to the reduction in work and/or school contacts. For most countries the basic reproduction number decreases from the week to weekends and regular to holiday periods by about 21% and 17%, respectively. However for other countries no significant decrease was observed. Conclusion We use a large-scale social contact survey in eight different European countries to gain insights in the relative change in the basic reproduction number on weekdays versus weekends and during regular versus holiday periods. The resulting estimates indicate that school closure can have a substantial impact on the spread of a newly emerging infectious disease that is transmitted via close (non sexual) contacts.

In several prior articles I have attempted to analyze and simplify the subject of immunological functions induced by vaccination that correlate with protection against later exposure to pathogens. Other authors have also written on the subject, and recently we jointly proposed terminology to bring some semantic clarity to the field. The generalization that vaccine-induced antibodies prevent acquisition whereas cellular immune functions clear infection still holds true, but that simple distinction becomes blurred in many instances. Specific antibody and cellular responses are multiple and redundant, so that vaccines for some pathogens protect through more than 1 immune function. Thus, this article aims in the direction opposite to simplicity to depict the complexity of correlates, or rather the complexity of mechanistic immune functions that contribute to protection. Nonmechanistic correlates that are practically useful but not truly protective will be mentioned in passing.