Operators ask this because they are planning: can one treatment cover the outbound and the return, or the whole trip? The honest answer is that it depends on the method, and for the method we perform the answer is precise. Pre-embarkation disinsection covers one flight sector.
One flight sector
Pre-embarkation treatment is performed on the empty aircraft at the last port before the destination country, before boarding, and it counts for that flight. That is how the WHO describes it and how destination authorities read it. The certificate we issue records the flight the treatment covers.
The reason is straightforward. The aerosol treatment kills what is aboard at the time and protects the cabin through the sector; it is not designed to be a lasting barrier across days of subsequent operations, ground stops and door openings.
What that means for a round trip
The outbound leg from the US to a country that requires disinsection is covered by treatment at your US departure airport. The return leg to the US is not subject to a US disinsection requirement. If your itinerary continues from the first destination to a second country that also requires disinsection, that leg needs its own consideration, and it will not be performed by us in the US. This is exactly the kind of routing question to send us before you file; we will tell you what applies leg by leg.
What about multi-stop routings to the destination
Because pre-embarkation is performed at the last port before the destination country, a stop between the US and the destination changes the plan. A US departure that stops in Hawaii on the way to Australia, for example, is treated at the last US port before Australia, which is the Hawaii stop rather than the mainland departure. A stop in a third country on the way to the destination raises the question of where the treatment can be performed at all. Send us the full itinerary and we will confirm exactly how to plan it.
Other methods, other durations
The WHO also recognizes a residual method, a surface treatment applied on the ground with the aircraft empty, whose period of validity is set by the destination authority. It is one of the four WHO methods; it is context, not something we offer. Pre-departure and on-arrival treatments count for the flight or arrival on which they are performed.
The practical rule
Plan disinsection per international arrival that requires it, and for US departures, plan it at the last US port before the destination. Send us the routing and we will confirm the plan for your aircraft, sector by sector.