@FinchTH It's possible that the period when the main advice of "wear a surgical mask with a tight-fitting cloth mask over it" could have been when following the advice (which some did, obviously not all that many) resulted in the best effectiveness in practice.
@FinchTH 可能是“戴上带有紧身布口罩的外科口罩”的主要建议可能是在遵循建议时（有些人确实这样做了，显然不是很多）导致了最佳效果在实践中。