A new vaccine for porcine reproductive and respiratory syndrome (PRRS) has been shown to overcome maternal immunity in newborn piglets, offering protection from this costly disease from before weaning through slaughter.

Speaking to Pig Health Today at the recent PROHEALTH Symposium in Ghent, Belgium, Tom Meyns, DVM - a swine veterinarian at Zoetis - said vaccination has long been an effective strategy for controlling PRRS, which causes a host of reproductive issues in sows as well as mortality, illness and production losses in growing pigs.

Typically, pigs are vaccinated against PRRS around two to four weeks of age, when maternally derived antibodies (MDA) are low enough not to interfere with the vaccine’s ability to trigger the desired immune response. However, Meyns said, this can leave a gap in protection between the loss of MDA and the onset of active immunity, leaving pigs vulnerable to PRRS infection when disease risk is highest.

“We see in most cases in Europe that pigs become infected shortly after weaning or in the nursery period, when infection pressure is very high,” Meyns said. “So if we can protect these animals from a young age, it’s really beneficial.”

To this end, scientists at Zoetis conducted a study - published in Porcine Health Management - to determine the efficacy of a commercial, modified-live virus (MLV) vaccine for PRRS in the presence of MDA.

The study was conducted in piglets born from sows that had received the vaccine, ensuring the piglets had maternal immunity. One group of piglets was vaccinated at day 1, according to label instructions, and the other served as unvaccinated control.

At 10 weeks of age, when MDA were gone, all piglets were infected with a European PRRS virus field strain (PRRSV-1) and subsequently monitored for clinical symptoms and viremia.

Results demonstrated significant reductions in rectal temperature and nasal and oral shedding in vaccinated piglets, suggesting a protective effect of vaccination from 1 day of age. Tests also revealed that all vaccinated pigs were seropositive prior to disease challenge, indicating the development of an antibody response even in the presence of MDA.

“The study really shows that vaccinating piglets from day 1 of age…protects them from the time that they are weaned, so they’re protected during the whole life of the fattening pig,” Meyns said.

“For the farmer, this is a really convenient way of vaccinating because pigs at day 1 of age are very easy to handle…whereas vaccinating animals around weaning or during the weaning period is provoking more stress and is not really ideal. So this is really a new thing which has great implications for farmers.”

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