Preemptive Treatment With Acyclovir in Intubated and Mechanically Ventilated Patients With Herpes (PTH2)

Inclusion Criteria: * aged ≥ 18 year-old * invasive mechanical ventilation(MV) for 96 hours and planned to last for at least 48 hours longer * HSV reactivation in the throat (qualitative PCR positive for HSV on a throat swab) * Presence of 1 or less organ failure; organ failure being defined as a corresponding-organ SOFA score of 3 or 4 (for example, renal failure will be defined as a renal SOFA score of 3 or 4) * Effective contraception for patients of childbearing age, throughout the treatment period * Written consent from the patient, from a close relative or from the person of trust previously appointed (or inclusion procedure in emergency situations) * Under social security cover Exclusion Criteria: * Hypersensitivity to acyclovir and excipient * Pregnant or breastfeeding (controlled by a blood pregnancy test) * Patient who received an antiviral drug active against HSV (acyclovir, valacyclovir, gancyclovir, valgancyclovir, foscavir, cidofovir) in the previous 30 days * Duration of ventilation before randomization \>15 days * Neutropenia, defined by an absolute neutrophils count \< 1,000/mm3 * Solid organ or bone-marrow transplant * Immunosuppressive treatment (including steroids at a dose \>0.5 mg/kg/day of prednisone or equivalent for \>1 month) * HIV infection * Moribund, defined by a Simplified Acute Physiology Score (SAPS) II score at inclusion \>75 points * Decision of withholding/withdrawing care