Shedding and transmission of a live attenuated influenza A virus vaccine in pre-weaned pigs under field conditions

Gustavo Lopez Moreno, Jayaveeramuthu Nirmala, Christa Goodell, Marie Culhane, Montserrat Torremorell

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Influenza A virus (IAV) is one of the most important respiratory viruses affecting pig health and vaccination is the most common strategy to control influenza infections. In this field study we assessed the onset and duration of shedding of a live attenuated influenza virus (LAIV) vaccine, its ability to transmit to non-vaccinated pigs and whether the LAIV could be aerosolized and detected in the environment. Thirty-three litters (n = 33) of a farm using the LAIV vaccine were selected for the study, a subset of them (n = 12) were left unvaccinated and a subset of piglets (n = 3) in vaccinated litters were also left unvaccinated to serve as sentinels. Selected piglets from the litters were sampled multiple days post vaccination (DPV) by collecting nasal swabs and blood, and were tested using a LAIV vaccine specific RT-PCR assay and hemagglutination inhibition assay against the LAIV strains respectively. Environmental specimens consisting of air and surface wipes were also collected. One hundred percent (21/21) of the vaccinated litters tested LAIV positive 1 DPV and until 6 DPV. In contrast, only five (5/33) of the thirty-three non-vaccinated pigs tested positive during the course of the study. Viable LAIV was confirmed in vaccinated pigs by cell culture and whole genome sequencing. In addition, low levels of LAIV RNA (RT-PCR Ct values ranging between 33 and 38) were detected in all air specimens collected on the day of vaccination and until 6 DPV (3/10). Pigs had maternally derived antibodies reactive against the LAIV strains which may have influenced the degree of shedding observed. Under the conditions of this study, shedding of the LAIV from vaccinated pigs was limited in time, resulted in minimal transmission to non-vaccinated pigs and was detected in low levels in aerosols collected in the vaccinated rooms likely influenced by the presence of maternally derived antibodies against the LAIV strains.

Original languageEnglish (US)
Article numbere0246690
JournalPloS one
Issue number2 February
StatePublished - Feb 2021

Bibliographical note

Publisher Copyright:
© 2021 Lopez Moreno et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


  • Aerosols
  • Animals
  • Antigens, Viral/analysis
  • Hemagglutination Inhibition Tests
  • Influenza A virus/immunology
  • Influenza Vaccines/administration & dosage
  • Orthomyxoviridae Infections/immunology
  • Swine
  • Swine Diseases/prevention & control
  • Vaccination
  • Virus Shedding

PubMed: MeSH publication types

  • Research Support, Non-U.S. Gov't
  • Journal Article


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