Figure 2. VSV replicon vaccines protect chickens from HPAIV challenge in a dose-dependent manner.

Chickens (group size n = 5) were immunized (i.m.) once or twice with VSVΔG(HA_H5-HP) using the indicated doses and subsequently challenged by intranasal inoculation with 10⁶ TCID₅₀ of A/whooper swan/Mongolia/3/2005 (H5N1). The animals were surveyed daily for survival (a) and clinical symptoms (b). The animals were scored as follows: (0) healthy, (1) ill (animals show one of the following symptoms: apathy, ruffled feather, anorexia, diarrhea, cyanosis of the exposed skin, comb and wattles, edemas of the face and/or head, neurological symptoms), (2) severely ill (severe or more than one of the symptoms mentioned above), and (3) dead. A daily clinical index representing the mean value of all chickens per group was calculated. For analysis of virus shedding oropharyngeal (c) and cloacal (d) swabs were taken from each animal at daily intervals for a period of 8 days post infection. RNA was extracted from the swabs and analyzed for the presence of viral RNA segment 7 by quantitative RT-PCR.