Results
To investigate the use of automated activity monitors in influenza
vaccine studies, we performed an immunization study in the commonly used
Influenza A/PR8 model. Mice were subcutaneously vaccinated with a single
dose of HA (Influenza A/PR8) formulated in the CAF01 adjuvant, which has
previously been evaluated in influenza virus animal
models3,4. On day 18, the mice were identified with
RFID transponders and observed for 6 days to set baseline activity
before being challenged on day 24. Unvaccinated mice were used as
controls. Subsequently, the mice underwent intranasal PR8 challenge (15
µl per nostril with 150 EID50) on day 24 and were
followed for 7 days. Daily weight monitoring was conducted, and virus
titers were determined from nasal washes on days 4 and 7 post-challenge,
as well as from lung homogenate on day 7 post-challenge. On day 7, a
significant difference in weight loss was observed between the
unvaccinated and the HA+CAF01 vaccinated groups (Figure 1A). Mice
vaccinated with HA+CAF01 had significantly higher activity levels than
the unvaccinated group from day 5 to day 7 (Figure 1B). Thus, influenza
infection led to reduced activity, whilst vaccination prevented this
reduction. Vaccination also led to a lower overall symptom score (Figure
1C). Weight loss correlated significantly with reduced activity (Figure
1D) and by following the decline in activity in individual mice in the
unvaccinated group, it could be seen that the decline in activity
directly preceded weight loss (sFig 1). Specifically, declined activity
could already be observed at day 3 in two of three mice, whereas weight
loss in these first occurred at day 5. By measuring nasal wash virus
titers by RT-PCR on day 4 post-challenge, we detected virus in four of
six HA+CAF01 vaccinated mice, although titers were significantly lower
compared to the unvaccinated group on both days 4 and 7 (p<0.01)
(Figure 1E). At day 7, virus was detected in all unvaccinated mice but
not in the mice that had received HA+CAF01 (Figure 1E). Overall, these
data demonstrate that vaccination using a single dose of HA+CAF01
vaccine effectively protected against influenza infection, reduced
activity, and disease. In contrast unvaccinated mice had a decrease in
activity, which preceded weight loss.