Norvax Compact 4

15 March 2003

Norvax® Compact 4 is a vaccine containing Aeromonas salmonicida subsp.salmonicida, Vibrio salmonicida, Vibrio anguillarum serotype O1 and Vibrio anguillarum serotype O2a. The vaccine induces protective immunity in Atlantic salmon against furunculosis (see Newsletter 5) caused by Aeromonas salmonicida subsp. salmonicida, coldwater vibriosis caused by Vibrio salmonicida, vibriosis  (see Newsletter 5) caused by Vibrio anguillarum serovar O1 and/or Vibrio anguillarum serovar O2a. Inactivated bacterial cultures are incorporated in a water-in-oil emulsion in order to enhance and prolong the immunity.

The onset of immunity is documented from 500 degree-days. Duration of immunity has been proven for 33 weeks by challenge studies and for 47 weeks by antibody studies under laboratory conditions. No outbreaks have been seen in field trials. 

Efficacy and Duration of Immunity Study
The efficacy and duration of immunity following vaccination of Atlantic salmon with one dose of Norvax® Compact 4 was investigated by means of challenge experiments and measurements of specific antibodies. The trial was carried out at VESO Vikan AkvaVet in Norway.

A total of 715 Atlantic salmon (average weight 26 grams) were vaccinated with Norvax® Compact 4 while untreated fish were used as controls. The groups were tagged and kept separate until challenge. 

At 6 and 33 weeks post vaccination, fish from each of the experimental groups were transferred to challenge units. The fish were challenged by i.p. injection. After each challenge, the mortality among vaccinated fish and controls were registered daily for three weeks.

Lower mortality (P<0.001) was obtained in vaccinated fish compared with controls in all challenge experiments. The RPS values are presented as RPS60 in Table 1. [RPS = (1 - M/60) x 100 where M = mortality among vaccinated fish at 60% control mortality].

Table 1. RPS60 values after bacterial challenges at 6 and 33 weeks post vaccination.

The serological response to the vaccination with Norvax® Compact 4 was monitored with ELISA tests. The antibody response against all antigens increased from 6 to 33 weeks post vaccination. 

Conclusion
The results of the challenge experiments at both 6 and 33 weeks post vaccination in addition to the high and increasing levels of specific antibodies against all four bacterial components demonstrate a duration of immunity against Aeromonas salmonicida subsp. salmonicida, Vibrio salmonicida, Vibrio anguillarum serovar O1 and Vibrio anguillarum  serovar O2a for at least 33 weeks.