MaxiVac™-FLU
A New Vaccine For Swine Influenza
Dr. Richard L. (Rick) Sibbel
SyntroVet Incorporated

The economic losses that occur due to respiratory disease in pigs have been well documented.1,2 Swine Influenza Virus (SIV) is recognized as a significant contributor to the complex respiratory disease syndrome in pigs.3 SIV causes a primary disease characterized by low mortality, high morbidity, and a relatively short duration. SIV can also predispose to secondary bacterial infections.4

Studies to determine the prevalence of SIV antibodies in the U.S. swine population have shown a high incidence (average of 30 percent) of SIV exposure.5 Regional differences were also noted, as the North Central U.S. had a higher (51 percent) seroprevalence to SIV. This same study confirmed the H1N1 subtype of SIV to be the predominant subtype in the U.S. pig population.

Vaccination as a means of controlling SIV infection and its consequences is well documented in European swine herds.1 The high seroprevalence of swine influenza in the U.S., combined with the success of SIV vaccination in Europe, indicated a role for a SIV vaccine in the U.S. This report provides a brief summary of data developed by SyntroVet during the licensing of MaxiVac™-FLU, the first SIV vaccine available in the U.S. This product is an inactivated, oil-adjuvanted vaccine containing the H1N1 subtype of SIV. Some recent field observations following use of MaxiVac-FLU are also presented.

The efficacy of MaxiVac-FLU in preventing clinical disease was demonstrated in a study in which seronegative, weaned pigs were given two doses of vaccine, three weeks apart, followed by aerosol administration of virulent SIV two weeks later.6 Vaccinated pigs shed less challenge virus in nasal secretions and had significantly lower clinical scores than non-vaccinated pigs. Lung pathology and virus recovery from lung homogenates was significantly reduced in MaxiVac-FLU vaccinates as compared to controls.

Studies to evaluate the protection offered by maternal antibody have also been described, and indicate that piglets from sows vaccinated with two doses pre-farrowing were clinically protected at 5 weeks of age.6 This study also showed that maternal antibody levels had waned to non-protective levels by the time piglets were eight weeks of age. Studies to determine optimum vaccination schedules in piglets from vaccinated sows are currently underway.

Veterinary practitioners routinely associate the acutely ill, coughing pig with swine influenza. This is commonly seen in nursery pigs and in pigs just introduced into the grow/finisher. Field vaccination protocols were developed to evaluate MaxiVac-FLU vaccination as a practical tool for control of SIV infection, and to monitor important economic parameters following vaccination in production systems. Following diagnostic confirmation of swine influenza in different herds, studies were initiated with MaxiVac-FLU, and the following observations were reported. Vaccination with MaxiVac-FLU at 4-5 weeks of age, followed by a second dose 2-3 weeks later, eliminated the coughing and anorexia historically seen in these nurseries.7 Similarly, immunization of pigs 2-3 weeks prior to placement in the grow/finisher reduced respiratory disease and decreased the days to market.8 The use of MaxiVac-FLU in commingled, multi-source feeder pigs was shown to be clinically beneficial. In this trial, herd performance improved when the vaccine was administered either prophylactically or in the face of an outbreak.9

Controlled studies and field experience demonstrate the benefits of SIV vaccination in infected herds. Studies are currently underway to quantify the economic benefits associated with MaxiVac-FLU vaccination in common husbandry situations. It is evident that SIV vaccination can play an important role in swine respiratory disease management.

1. Christensen, G. and Mousing, J. 1992. In Diseases of Swine, Eds.: Leman, A.D., et al, 7th Ed., Iowa State University Press, Ames, IA. Respiratory System, pp. 138-162

2. Straw, B., 1992. Controlling Pneumonia in Swine Herds. Vet Med. 87:78-86

3. Halbur, P.G., Paul, P.S., and Janke, B.H., 1993. Viral Contributors to the Porcine Respiratory Disease Complex. Proc. Am. Assoc. Swine Prac., pp. 343-350.

4. Scatozza, F., and Sidoli, L., 1986. Effects of Haemophilus Pleuropneumonia Infection in Piglets Recovering from Influenza. Proceedings Int. Pig. Vet. Soc., p. 150.

5. Chambers, T.M., et al., 1991. Influenza Viral Infection of Swine in the U.S. 1988-1989. Archives of Virology 116: 261-265.

6. Brown, G.B., and McMillen, J.K., 1994. MaxiVac-FLU: Evaluation of the Safety and Efficacy of a Swine Influenza Vaccine. Proc. Am. Assoc. of Swine Prac., pp. 37-39.

7. Groff, B.T., 1994. Personal communication.

8. Lang, T., 1994. Personal communication.