There are two main approaches. The first involves administering antibodies, either taken from convalescent patients or engineered in laboratories. Timing is key.

For example, in the case of the infection caused by the respiratory syncytial virus (RSV), a severe lung disease that affects young children, giving antibodies to subjects before they are exposed to the virus protects them from contracting the disease. But antibodies given to children who already suffer respiratory failure brought on by RSV do not reduce the duration of mechanical ventilation or recovery time…

Another kind of treatment for acute viral infections involves drugs that kill the virus in the patient’s body or prevent its replication — and those, too, typically are effective only during the early, usually mild, phase of the diseases…

When a person comes down with chickenpox — usually it’s a child, as most adults are immune, having either had the disease as children themselves or been vaccinated — giving the antiviral drug acyclovir to other children in the household before they display any sign of the illness confers to them virtually total protection against it. Better still, they then develop protective antibodies against the virus and become immune.