Vaccines generally are not protective before 7 to 20 days after administration. Morbidity and mortality due to viral infections may be recorded in kittens during this period and represent major risks in crowded shelters. The efficacy of a recombinant feline omega interferon (rFeIFN) was evaluated for the prevention of infections in kittens recently introduced into a shelter. Recently vaccinated kittens were allocated into 2 groups: 36 cats were injected with 1 MU of rFeIFN (group T), while 52 cats remained untreated (group C). The cats were observed over a 15-day follow-up period. Treatment preventive efficacy was evaluated from morbidity over 15 days following the 1st veterinary consultation (V1). Animal characteristics were compared between the groups using the Wilcoxon rank sum test. The percentage of diseased cats was compared between groups using Fisher's exact test. At V1, the 2 groups did not differ for any of the parameters. After 15 days, 10 cats had shown clinical signs of infection. Four cases of panleucopenia confirmed by PCR (with 1 fatal outcome) and 3 cases consistent with a coryza-like infection were observed in group C. Only 1 cat showed signs of coryza in group T. Fewer infectious episodes were thus recorded after rFeIFN preventive treatment (p=0.0429). These results show the interest of rFeIFN in reducing the risk of viral infection in the few days following vaccine injection, while the animal is not yet protected by the immune response.