1. Department of Virology Statens Serum Institute, DK-2300 Copenhagen, Denmark and Department of Virology, Institut Pasteur, 75724 Paris Cedex 15, France
2. Department of Virology Statens Serum Institute, DK-2300 Copenhagen, Denmark
3. Department of Clinical Biochemistry, Statens Serum Institute, DK-2300 Copenhagen, Denmark