Infectious bronchitis virus is an RNA virus that causes respiratory symptoms and is found around the globe. RNA viruses have a single strand of nucleotides encoding their genome, so they are prone to mutations. These mutations can result in new serotypes or there can be a genetic shift when recombination occurs when there is more than one virus in a cell replicating at the same time. Either way, changes in the viral genome can lead to antigenic changes in the protein outer casing of the virus.

Dr. Mark W. Jackwood, professor and head of the Department of Population Health, College of Veterinary Medicine, University of Georgia, said there is little cross protection provided when birds are vaccinated with one serotype of IBV and then challenged with a relatively distantly related serotype. He told the audience of the WATT webinar, A complete respiratory package lets you breathe easy, that some broiler companies are vaccinating with multiple serotypes of IBV.

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Jackwood said that research in Europe identified two vaccine serotypes that did provide a level of cross protection against several other serotypes of IBV, when protection is measured as maintaining activity in tracheal cilia in the challenged birds. Similar tests were performed in Jackwood's laboratory to identify a combination of vaccine serotypes approved for use in the U.S. which offered cross protection from IBV serotypes commonly found in the U.S.

Jackwood's research found that a combination of IBV serotype vaccines called Ma5 (Massachusetts 5) and Del072 (Delaware 072) administered at one day of age offered protection that maintained tracheal cilia activity when the birds where challenged with a variety of IBV strains. Dr. Charles Broussard, technical manager, Merck Animal Health Poultry Marketing Group, said that for small broilers a single vaccination at day of age with the Ma5 and Del072 vaccine provides good protection and that for big bird programs it is recommended that a second vaccination be given at 14 days of age.