2.3. Efficacy studies
2.3.1. Laboratory studies
The onset of immunity (OOI) and duration of immunity (DOI)
for each of the two vaccine antigens were determined in experimental
challenge studies (Table 1). In each experiment, 3 week
old pigs from herds free of M. hyopneumoniae and seropositive
for PCV2 were randomly divided in two groups (vaccine and control)
at the time of vaccination. Blood samples were taken just
before vaccination, at the time of challenge and 2 (PCV2 challenge
studies only) and 3 weeks after challenge. In the DOI studies, blood
samples were also taken at regular intervals between vaccination
and challenge.
PCV2 challenge was done by intranasal instillation (3 ml per
nostril, ±106 TCID50) of a recent Dutch field isolate at 2 wpv or
22 wpv. Three weeks after PCV2 challenge, all pigs were