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Cross protection studies - inactivated vaccines

Cross protection may also be obtained after the use of an inactivated vaccine. The following experiment carried out in layer birds vaccinated with a Massachusetts inactivated vaccine and challenged with pathogenic IBV 4/91 illustrates this phenomenon.

Experimental design

Experimental design

Group	Primed with IB		Inactivated vaccine
	Day old	6 weeks	16 weeks
Vaccinated	Ma5	4/91	Massachusetts
Controls	-	-	-

• The birds were bled at 16, 22, 28, 34, 40, 46, 50 and 56 weeks. Data in results shown from 16, 22 and 50 weeks of age.
• Samples were tested by the VN tests for antibodies against IBV 4/91
• Protection against IBV 4/91 was assessed by the ciliostasis test (10 birds/group) following challenge of the hens at 56 weeks of age

Results

1. Antibody titres after vaccination
   
2. Ciliostasis index after challenge( lower average ciliostasis index numbers indicate protection)
   

Conclusion

• A good antibody response and a good level of protection against IBV 4/91 can be achieved by a vaccination program based on a live priming with Nobilis IB Ma5 (Massachusetts type) and Nobilis IB 4/91, followed by vaccination with an inactivated vaccine of the Massachusetts type.
• This program will boost titres throughout the life cycle of the hens not only against Massachusetts but also against IBV 4/91.
• The results confirm the validity of the concept of cross-protection and emphasise the importance of carefully designing vaccination programs to control new serotypes under field conditions.