Countries can choose to use the Janssen (Ad26.COV2.S) vaccine as a schedule with a single or two doses. A single dose is sometimes preferred in countries to reach rapid widespread coverage and to protect hard-to-reach populations, but administration of the second dose will result in increased individual-level protection against symptomatic infection and against severe disease. WHO recommends an inter-dose interval of 2 to 6 months. The choice for the inter-dose interval depends on the epidemiological situation and needs for certain subpopulations.