1 Immunization Unit, Robert Koch Institute, Berlin, Germany. Electronic address: NygrenT@rki.de.
2 Immunization Unit, Robert Koch Institute, Berlin, Germany.
3 Bavarian Health and Food Safety Authority (LGL), Munich, Germany; Institute of Social Medicine and Health Systems Research, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany.
4 State Health Office Baden-Wuerttemberg (LGA), Stuttgart, Germany.