Interference of maternal antibodies with the immune response of foals after vaccination against equine influenza

Abstract

SUMMARYThe purpose of the study was twofold First, using two groups of 22 foals each, we investigated the extent to which maternal antibodies interfere with the humoral response against equine influenza. The foals were born to mares that had been vaccinated twice yearly against influenza since 1982. Foals of group I were vaccinated three times at early ages (12 16, and 32 weeks of age), and foals of group II were likewise vaccinated but at later ages (24, 28, and 44 weeks of age). After the first and second vaccinations, neither group showed an increase in antibodies that inhibit haemagglutination. Group II foals, however, had a significantly stronger antibody response against nucleoprotein after the second vaccination than the foals ofgroup I. After the third vaccination, group II foals had a significantly stronger and longer lasting antibody response against haemagglutinin than the foals of group I. However, the antibody response to nucleoprotein was comparable in both groups.Second, the foals of group II were studied to determine the persistence of maternal antibodies directed against a common nucleoprotein and the haemagglutinin of two strains of equine influenza A virus. Biological half-lives of 39, 32, and 33 days were calculated for maternal antibodies directed against haemagglutinin of strains H7N7 Prague and H3N8 Miami, and against the nucleoprotein respectively. Maternal antibody titres at the time of vaccination were closely related to the degree of interference with the immune response. Because even small amounts of maternal antibodies interfered with the efficacy of vaccination, we conclude that foals born to mares vaccinated more than once yearly against influenza virus should not be vaccinated before 24 weeks of age.

Equine viral vaccines: the past, present and future

“…Apart from vaccine potency (see below) and strain composition, the timing of vaccination is important and can have an impact on vaccine efficacy. It is well accepted that even low levels of maternal antibodies can interfere with successful immunisation [20,94,96] and determine the proper time of vaccination. The disappearance of these antibodies can be monitored by Haemagglutination Inhibition (HI), Single Radial Haemolyis (SRH) or Enzyme Linked Immunosorbant Assays (ELISA) and the results of several independent studies [20,94,96] have shown that the majority of foals born to vaccinated mares should not be vaccinated before 24 weeks of age.…”

Current perspectives on control of equine influenza

“…The temptation is to vaccinate elite stock prior to the loss of maternal antibodies to avoid any window of susceptibility. Foals born to mares vaccinated during the gestation period have high levels of maternal antibody within two days of birth [13,61,63]. In contrast to Liu et al [32], who reported that maternal antibody persisted for only a short period, several authors [13,61,63] found that the majority of foals they tested had detectable (HI) antibody titres at three months of age but these had virtually disappeared at six months.…”

“…Foals born to mares vaccinated during the gestation period have high levels of maternal antibody within two days of birth [13,61,63]. In contrast to Liu et al [32], who reported that maternal antibody persisted for only a short period, several authors [13,61,63] found that the majority of foals they tested had detectable (HI) antibody titres at three months of age but these had virtually disappeared at six months. Cullinane et al [13] suggested that not only does vaccination in the face of maternal antibody interfere with the development of active immunity but that repeat vaccination in the face of maternal antibodies may induce tolerance.…”

“…The safety and efficacy of the vaccine has been demonstrated in experimental studies, however the vaccine does not provide sterile immunity [10,34,60,71]. No correlation was found between the concentration of serum antibody induced by vaccination and protection against infection, though an anamnestic response was demonstrated at seven days post infection [61]. Although there is evidence to show that primed animals will develop a serological response [71], it appears that the use of serum antibody response as a measure of live virus mucosal vaccines in naïve animals is inappropriate.…”

“…However it is questionable whether the preliminary programme of three doses followed by annual vaccination provides sufficient immunity to protect young horses from the disease or individual training yards from small outbreaks of influenza. The short-lived immunity provided by inactivated vaccines has been acknowledged for some years, and it is apparent from various studies [13,61,63] that vaccination in accordance with the minimum requirements of Jockey Club rules and the vaccine manufacturer's recommendations leaves horses with low antibody titres for several months between their second and third vaccination. Newton et al [46] found that SRH antibody levels in yearling Thoroughbreds on studs in Newmarket declined below a protective level within four months of a booster vaccination.…”