Safety issues of veterinary vaccines

Prof. Lars Erik Larsen

Institute for Veterinary and Animal Sciences,
University of Copenhagen, Denmark


Lars Erik Larsen (born 1963) holds a full professorship in veterinary virology and has worked with virus infections in production animals for the last 20 years. He has been involved in research on swine viruses (diagnostic tools, molecular epidemiology, vaccinology and basic pathogenesis) for the last 15 years. Since 2010, he has been responsible for the Danish diagnostic preparedness program and chairs the Danish expert committee for animal influenza viruses. Lars has participated in several national and European projects on enzootic swine viruses with focus on PRRSV, PCV-2 and swine influenza virus. He is the head of the enzootic/zoonotic virus research group at UCPH and is scientifically responsible for the national surveillance program for avian and swine influenza viruses. Lars is also responsible for the teaching of veterinary students in veterinary virology and is supervisor of a range of PhD, Master and Bachelor students. Lars is currently board member of the Danish Society of Virology and the Danish Pig Veterinary Society. He has published more than 100 international peer reviewed papers on veterinary virology and has co-authored more than 300 other publications.


Modified live virus (MLV) vaccines have been extensively used in human and veterinary medicine for decades. Traditionally, the virus strains included in MLV vaccines have been attenuated by repeated passage in vitro to decrease its capability to induce clinical disease in the vaccinated host. Despite the attenuated phenotype, most MLVs strains are excreted from the host and may infect unvaccinated animals. This in turn imply the risk that the attenuated vaccine strain may revert to virulence.

The presentation will critically evaluate the risks and benefit of use of MLVs in pigs. Are the safety data required for MLVs to be licenced adequate… or could we do better? What is the consequence of off-label use of these vaccines, e.g. are mass-vaccination 3-4 times a year necessary, have the vaccines been tested in these settings, and what are the risks? “Unspecific effects” of vaccines is a hot topic in human vaccinology….does this apply also to veterinary vaccines?

Finally, a couple of cases with PRRSV MLVs will be presented to illustrate how wrong things can go!