Abstract: Does Vaccine-Induced Maternally-Derived Immunity Protect Swine Offspring against Influenza a Viruses? A Systematic Review and Meta-Analysis of Challenge Trials from 1990 to May 2021
Simple Summary: Vaccinated mother pigs can pass vaccine protection (immunity) onto their offspring, but in the case of influenza, the benefit is not clear. Influenza viruses evolve rapidly and can sometimes change their appearance to the point of becoming a new stain that evades a pig’s immune defenses. It is believed that matching the vaccine to the virus is important for protection. To predict if a vaccine is protective it is, therefore, also important to know how closely it matches the influenza strain or strains circulating in the herd. For the first time, we apply the methods of evidence-based medicine to understand if vaccinating sows results in the protection of their piglets from influenza. We were only interested in studies where the researcher knew if the vaccine matched the infecting virus. These types of studies are called challenge trials because researchers controlled both the vaccines used in the mother pigs and the strain of influenza viruses used to infect the piglets. We looked at scientific studies published over twenty years and considered many ways to measure protection. We found piglets from vaccinated sows took a little bit longer to shed the virus if they became infected and that less virus was found in piglets where their mother’s vaccine matched the virus used to infect the piglet. In modern commercial farms, however, piglets are often exposed back-to-back or at the same time to the same, or more often, to more than one strain of influenza. Also, viruses behave differently in herds than they do in small studies because the number of pigs in a herd is many times greater. Because most studies involved simple exposures in small groups of pigs and only one small study looked at a back-to-back exposure with the same strain of influenza, it is difficult to know if our findings can be further extended into the real world. Despite this, the body of research was useful to show the importance of matching. We also learned that additional research is still needed and importantly, that there is room for improvement in how influenza vaccine studies in pigs are reported. Influenza vaccine research is complex in pigs and it is important to understand the type or types of virus strains involved in each study. Future research is needed where researchers are able to identify all infecting strains of influenza and the piglets experience real-world influenza virus exposures.
Keay S, Poljak Z, Alberts F, O’Connor A, Friendship R, O’Sullivan TL, Sargeant JM. Does Vaccine-Induced Maternally-Derived Immunity Protect Swine Offspring against Influenza a Viruses? A Systematic Review and Meta-Analysis of Challenge Trials from 1990 to May 2021. Animals. 2023; 13(19):3085. https://doi.org/10.3390/ani13193085