Detection of Vaccinia DNA in the Blood Following Smallpox Vaccination

Detection of vaccinia virus DNA, but not infectious virus, in the blood of smallpox vaccine recipients

“…No smallpox vaccinees had detectable infectious virus based on cultures from the blood or throat, including blood at the same time points from the same patients which were PCR-positive. One recent study reported negative results for detection of vaccinia in the blood or throat using conventional culture and PCR [4], while another study that used PCR alone detected vaccinia virus DNA at both of these sites [6] (Table 2). …”

“…Thus, our results may differ from those of the prior study that did not detect vaccinia virus DNA in blood [4], since we used 40-times the amount of blood for PCR when compared to the older study and we used fresh blood that had not been frozen and thawed. In another study that detected viral DNA in 5 blood specimens by PCR [6], the authors extracted 0.1 ml of DNA from 1 ml of plasma and used 0.005 ml of extract for each 20 ul real-time PCR reaction (M. Savona, personal communication).…”

“…Srinivasan and colleagues reported negative cultures from plasma and whole blood for vaccinia in 665 specimens from 95 vaccinees [5]. In 2006 Savona et al detected about 1,000 copies of vaccinia genome DNA per milliliter in the blood by PCR in 5 of 77 vaccinees (5 of 125 specimens) receiving Dryvax vaccinia; vaccinia cultures were not performed [6]. Vaccinia DNA was detected by PCR in the blood in 4 patients at 6 to 8 days after vaccination and in 1 patient at 20 to 22 days after vaccination.…”

“…Klote et al in 2005 evaluated throat swabs from 144 Dryvax vaccinees (801 specimens) and found no evidence of virus by PCR, culture, or antigen detection [7]. In contrast, Savona et al detected virus DNA in throat swabs in 11 of 77 vaccinees (12 of 125 specimens) by PCR [6].…”

“…While vaccinia virus DNA has been detected by PCR in both blood and throat swabs in one study, cultures for the virus were not performed [6]. Since detection of viral DNA by PCR does not indicate that infectious virus is present, we tested blood and throat swabs from vaccinees by both PCR and shell vial culture for vaccinia virus.…”