Source & further information: http://www.ecdc.europa.eu/en/aboutus/jobs/Pages/seconded-national-expert.aspx

Seconded National Expert (SNE)

The spirit of the SNE cooperation is to enhance and develop the relationship between national institutions throughout Member States of the European Union. Seconded National Experts remain in the service of their employer throughout the period of secondment and continue to be paid by that employer. The contract duration is for full time employment and is generally 6 to 24 months (to be agreed between the current employer and ECDC). The contract is renewable once or more but the total duration of secondment cannot exceed four years.