Celvapan

Data on vaccination against influenza virus were provided by the Norwegian Immunisation Registry (SYSVAK) from 2006 through the beginning of 2013 [23 (link)]. Influenza vaccinations were not notifiable prior to the “swine flu” pandemic in 2009/2010, during which reporting of all influenza vaccinations to SYSVAK was mandatory and nearly complete. After the pandemic, that is, from the 2010/2011 season onwards, influenza vaccinations have been notifiable provided that oral consent is obtained from each vaccinee or parent/guardian [23 (link)]. Hence, there has been a considerable underreporting of influenza vaccinations during regular seasons. Therefore, we only considered vaccinations with Pandemrix H1N1^® (GlaxoSmithKline) and Celvapan^® (Baxter), which were vaccines used during the pandemic influenza outbreak. The proportion between the two vaccination types in the current study was 2.2 Celvapan^® vaccinations per 10 000 Pandemrix H1N1^® vaccinations. These will hereafter be referred to as pandemic vaccinations.

In Norway, the majority of laboratory-confirmed cases of influenza A (H1N1) infection were registered during the main pandemic wave from October 1^st through December 31^st, 2009 (Fig. 1). From October 19^th, 2009, two vaccines became available: Pandemrix® (GlaxoSmithKline), which contained the squalene-based adjuvant AS03, and Celvapan® (Baxter), which did not. Pandemrix® was the recommended vaccine for all ages, while Celvapan® was only offered to people with severe egg allergy. The vaccination period overlapped with the main period of the pandemic wave. However, a small number of vaccine doses were administered after the main pandemic wave (Fig. 1).Fig. 1

Timing of the influenza pandemic in Norway illustrated by number of laboratory-confirmed cases per week of influenza A (H1N1) (all ages) and the timing of the vaccination campaign given by the number of pandemic influenza vaccinations per week in children born in 2006–2009