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.