Skip to main content

Archived Comments for: In vitro host range, multiplication and virion forms of recombinant viruses obtained from co-infection in vitro with a vaccinia-vectored influenza vaccine and a naturally occurring cowpox virus isolate

Back to article

  1. Poxvirus vectors

    Bernard Moss, National Institutes of Health

    22 May 2009

    Okeke et al. caution against the extensive use of poxvirus vectors in general, and MVA in particular, because of the possibility of their recombining with naturally occurring poxviruses. It was well known, prior to the studies of Okeke et al., that deliberate infection of permissive cells with two orthopoxviruses could result in recombination. The important question is whether this is a significant risk in vivo. Fortunately, the experiment has already been done in a very rigorous manner with negative results. Replicating strains of vaccinia virus were given to millions of humans as the smallpox vaccine in smallpox endemic areas and no recombinants between variola (smallpox) virus and vaccinia virus have been reported; nor is there any evidence for this in the 49 variola virus isolates that have been completely sequenced. Indeed, vaccinia virus was routinely given to people who had already been infected by contact with smallpox patients. Surely, the opportunity for a non-replicating strain of vaccinia virus like MVA or another highly attenuated strain to recombine with a naturally occurring poxvirus would be far less than with the vaccine strains used in the past. If Okeke and collaborators wish to advance their hypothesis, as a worst-case scenario they should consider injecting MVA intramuscularly into a mouse and then infecting the mouse intranasally with cowpox virus.

    Competing interests