CANDID NO-1 ARGENTINE HEMORRHAGIC-FEVER VACCINE PROTECTS AGAINST LETHAL JUNIN VIRUS CHALLENGE IN RHESUS MACAQUES

The protective efficacy of Candid No. 1, a live-attenuated vaccine aga inst Argentine hemorrhagic fever (AHF), was evaluated in non-human pri mates. Twenty rhesus macaques immunized 3 months previously with grade d doses of Candid No. 1 (16-127, 000 PFU), as well as 4 placebo-inocul ated controls, were challenged with 4.41 log10 PFU of virulent P3790 s train Junin virus. All controls developed severe clinical disease; 3 o f 4 died. In contrast, all vaccinated animals were fully protected; no ne developed any signs of AHF during a 105-day follow-up period. Virem ia and virus shedding were readily detected in all placebo-vaccinated controls, while virus could be recovered only once (by amplification) from throat swabs of 2 Candid No. 1 vaccinees on day 21. Vigorous seco ndary-type neutralizing and immunofluorescent antibody responses were seen in most vaccinees that had received 3 log10 PFU Candid No. 1 or f ewer; all others, including those receiving 127,200 PFU, maintained re latively stable titers during follow-up. Candid No. 1 was highly immun ogenic and fully protective against lethal Junin virus challenge in rh esus macaques, even at extremely low (16 PFU) vaccine doses.