Impact of immunization with glycoprotein D2/AS04 on herpes simplex virus type 2 shedding into the genital tract in guinea pigs that become infected

In recent clinical trials, a vaccine that contained herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) and the adjuvant AS04 afforded HSV-seronegative women significant protection against HSV-2 genital disease and limited protection against infection. Similarly, in guinea pigs, immunization with the vaccine provided significant protection against genital HSV-2 disease but did not prevent mucosal infection. We explored the impact of immunization on the magnitude of latent virus infection and on the frequency and magnitude of virus reactivation as measured by both recurrent disease and viral shedding into the genital tract. Guinea pigs immunized with gD2/AS04 were shown by quantitative polymerase chain reaction (qPCR) analysis to have significantly less latent viral DNA in the ganglia than did naive control guinea pigs and to have a reduced incidence and frequency of recurrent disease. By contrast, all immunized guinea pigs shed virus into the genital tract with a frequency comparable to that seen in control guinea pigs. However, the amount of virus shed was significantly reduced, as measured by qPCR. These data suggest that immunization could affect transmission by altering viral shedding patterns.