Protective efficacy of a recombinant vaccinia virus in vaccinia-immune mice.

Recombinant viral vectors offer a potential means of vaccinating against diseases for which there are no current safe vaccines. One of the criteria on which a viral vaccine vector would be selected is that it either circulates in the human or livestock population without producing overt disease (e.g. adenovirus) or has a history as a safe vaccine (e.g. vaccinia virus). However, this selection criterion also means that the target population is likely to have circulating antibodies that are specific to the vaccine vector. Since a percentage of the world's population has been vaccinated during the World Health Organization's Smallpox Eradication Campaign, such antibody titres, which are likely to lower vaccine efficacy, have been raised as an objection to the use of recombinant vaccinia viruses as vaccines. We have tested the effect of vaccinia-specific immunity on the protective efficacy of a recombinant virus, VV-PR8-HA6 (1) which expresses the haemagglutinin of the influenza virus A/PR/8/34.