Taking in consideration the risk of thrombs by SARS-CoV-2 Spike (S) protein (because of its binding to cellular ACE2) and of amyloid brain plaques by its nucleocapsid (N) protein, it is necessary molecular (DNA, RNA and/or protein) vaccines be designed against other viral proteins, and boosting by siRNAs against virus genes, coding proteins S and N. In vitro-incubated mammalian cell cultures were inoculated with vaccine avipoxviral strains (Poxviridae family) FK (fowl) and Dessau (pigeon) with initial infectious titers 104CCID50/ml and 106.5CCID50/ml, respectively (initial infectious titers, in which was observed 50% cytopathological changes in the infected cells). Separate subpopulations of the so inoculated mammalian cells were freezed in the presence of cryoprotector Dimethylsulfoxide (DMSO), and others - with different concentrations of the methylxantine/purine analogs (Aminophylin and 61-Tartrate), at the 24-th and 48-th hours after the treatment with each substance, 24 hours after the viral inoculation. After thawing and reincubation, as a source of extracellular virus served the cultural fluids, and of intracellular - scraped cellular monolayers. The titers of the intracellular forms were significantly higher that these of the extracellular. Transfer of nucleotide (DNA and/or RNA) fragments between virus and cellular genomes, due to activated fusion on the influence of DMSO plus drastic temperature changes was proposed, which suggests possibilities for production of molecular vaccines and suppression of nonwished genes. 50% cell viability on the influence of the two methylxantine derivatives on in vitro-incubated cells was reached at dilution values between 10-4 M/ml in the cells, inoculated with strain FK, and 10-3 M/ml in the cells, inoculated with strain Dessau, at the 24-th hour after the virus inoculation. These results show the antiviral activity both purine analogs, by taking in consideration the observed higher virulency of strain FK (in higher dilutions of the viral suspension) compared with strain Dessau.