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Although the risk of smallpox virus being used as a terrorist weapon is very low, it is mandatory to examine potential vaccination strategies, and also the residual immunization rate in the general population. During revaccination of a national intervention team, the residual immunity of 184 volunteers was determined by assaying T memory cells in the gamma interferon ELISpot test, and central T memory cell responses in a proliferation assay. Three-quarters of the subjects had a proliferative response. This response was lower after the age of 55 years but could be reactivated by revaccination.

The construction of recombinant vaccinia viruses (VV) is definitely a promising approach to develop vaccines for pets. To produce safer VV recombinant vaccines, it is necessary to understand the pathogenesis of VV infection. The goal of this study was to compare the biological properties of the extracellular and intracellular infectious particles of VV. Four biological properties were investigated: (i) the binding into cellular receptor(s); (ii) the mechanism of entry; (iii) the resistance to neutralisation by antibodies; (iv) the resistance to complement lysis. The results obtained in this study emphasize the differences existing between the two infectious forms of VV and demonstrate the adaptation of the extracellular particle to its role of virus dissemination in vivo. The results of this study implicate that VV strains used as expression vector in vaccinology should be deleted for genes required for EEV morphogenesis.

Vaccination against smallpox should be discontinued in all countries except for individuals with a high risk of exposure (WHO, 1980). Since this vaccination is performed less and less often, one must expect complications to occur, the etiology of which may not be recognized. This course of events leads the authors to point out the difficulties in diagnosis and therapy of localized accidental vaccinia encountered in six patients hospitalized in Brest (1971-1979). Diagnosis is considered if the patient himself, or a person he came in contact with, was recently vaccinated. Diagnosis should always be established by virology. Such accidents can be avoided by a faultless vaccination technique and by giving sufficient information to the inoculated subject or to his relatives.

Human peripheral lymphocytes harvested 7 days after vaccination with vaccinia virus or measles virus lyse specifically target cells infected with the corresponding virus. This cytotoxic activity is found in a subpopulation of lymphocytes depleted of T-cells and containing lymphocytes bearing Fc receptor. The activity can also be transferred by supernatant of immune lymphocytes on addition of normal lymphocyte. These results suggest that two types of cell are involved: an antibody-secreting cell providing specific antiviral antibody (B-cells), and an effector cell bearing Fc receptor (K-cells).

Adsorption of chicken lymphocytes to HEp-2 cells infected with vaccinia virus was found to occur by two processes. In one, the lymphocytes were attached to the microvilli of the HEp-2 cells, and the lymphocyte and host cell were separated at a distance of up to 0.6 micron. In the other, there was direct and close binding of the lymphocytes to the infected HEp-2 cell. The lymphocyte and HEp-2 cell were separated by an apparent gap approximately 10 to 20 nm in width.