Effect of oral acyclovir against primary and secondary viraemia in incubation period of varicella.

The effect of oral acyclovir (approximately 40 mg/kg daily in four divided doses) against primary and secondary viraemia of varicella zoster virus (VZV) was examined in 27 children susceptible to VZV who were exposed to the virus in their families and their clinical features were compared with those of 19 non-treated subjects. The infection was confirmed by a fluorescent antibody to membrane antigen assay in 11 (85%) of 13 children who received acyclovir for the first seven days after exposure to VZV and in 11 (79%) of 14 who received acyclovir for the next seven days. The geometric mean antibody titre of the former group was significantly higher than that of the latter group. Varicella developed in 10 (91%) and was subclinical in one (9%) in the former group, whereas a very mild disease occurred in three (27%) and was subclinical in eight (73%) in the latter group. The severity of varicella was significantly greater in the former group than that in the latter group. On the other hand, all of the control group developed typical varicella and their clinical features were more severe than those of the acyclovir administered group. These data indicate that oral acyclovir more effectively inhibits replication of VZV in secondary viraemia than that of the primary viraemia.