People vaccinated in the EU or US do not need to isolate when coming to the UK from an amber country.
The move is in response to an attack on a vessel last week in which two people were killed.
Paul Bussetti will face a new trial after the High Court quashed his previous acquittal.
The charity says it is taking action following a "very small number of safeguarding incidents".
They came after the after the body of a boy, named locally as Logan, was found.