Table 1.

2018 prioritization criteria and weighting.

Criteria	Weights
Human-to-human transmission	23.87%
Severity or case fatality rate	16.25%
The human/animal interface	9.16%
The public health context of the affected area	13.78%
Potential societal impacts	12.85%
Evolutionary potential of the pathogen	12.58%
Other factors (including the pathogen's geographic range, shared epidemiological and/or genotypic characteristics with pathogens that pose an epidemic threat, the absence of robust protective immunity, a high risk of occupational exposure, or connections with biological weapons programmes)	11.51%

The prioritization criteria were first developed in 2015 by a group of experts (WHO, 2015), reviewed, validated and weighted by another group of experts in 2016 (WHO, 2016b). After the 2017 annual review and subsequent sensitivity analysis one of the criteria (availability of medical countermeasures) was moved to the disease screening phase of the process. Consequently, the remaining criteria were reweighted by a wider group of experts by using online survey. These criteria comply with the MDCA best practice: completeness, non-redundancy, nonoverlapping and preference independence (Marsh et al., 2016; Thokala et al., 2016).