We performed experiments to determine whether parenteral immunization with SA11 rotavirus can induce active protective immunity in a rabbit model of rotavirus infection. After one or two intramuscular injections of 1 ml of live or formalin-inactivated SA11 virus, we evaluated the mucosal and serologic immune response and protection from challenge with a high dose of live, virulent rabbit (Ala) rotavirus. Inactivated SA11 virus preparations, evaluated by enzyme-linked immunosorbent assay (ELISA) with a panel of VP4- and VP7-specific neutralizing and nonneutralizing monoclonal antibodies, did not show a loss of epitopes from the inactivation procedure compared with live virus. Administration of two doses of vaccine, one at zero days postvaccination (DPV) and a booster shot at 49 DPV, followed by challenge at 71 DPV with 3.5 x 10(5) PFU of Ala virus resulted in protection from challenge. None of the two-dose virus-vaccinated rabbits shed virus after challenge, while virus shedding was detected in all control rabbits (P = 0.001, Fisher's exact two-tailed test). Differences in total serum immunoglobulin (Ig) antirotavirus ELISA titers (P < 0.05, Wilcoxon's rank sum test) were observed between groups vaccinated with virus in aluminum phosphate or Freund's adjuvant but not between groups vaccinated with live or inactivated virus in either adjuvant. All rabbits given two doses of vaccine had detectable antirotavirus intestinal antibody of the IgG, but not IgA, isotype. After challenge, fourfold or greater increases in intestinal IgG antibody responses were observed in three rabbits, whereas all controls and all but one virus-vaccinated rabbit had an intestinal IgA antibody response. In contrast, vaccination of rabbits with one dose of SA11 followed by challenge at 21 DPV did not protect from challenge; no difference in the mean number of days of virus shedding between any of the vaccinated groups and controls was observed. A serologic, but not a mucosal, antibody response was observed after the one-dose vaccination regimen. Differences in serologic antibody titers were not observed between any of the one-dose virus-vaccinated groups. These data indicate that parenteral vaccination with two, but not one, doses of rotavirus in either Freund's adjuvant or aluminum phosphate can induce active protection from challenge.(ABSTRACT TRUNCATED AT 400 WORDS)