[palmer]

If that were true, everyone would have been wearing a mask full time for the last century.

The meaning of "complementary" is that they achieve the same goal. One or the other will work, but both together works better. People did indeed wear masks in 1918, lots of them in lots of places e.g.outdoor sporting events. Masks slowed the spread and impact of H1N1 and herd immunity did the rest.

[zeestephen]

Re: “The meaning of “complementary” is that they achieve the same goal.”

Thanks for clearing that up. I thought you misspelled complimentary.

The point of my previous post was that if masking actually prevents infections, then it is impossible to achieve herd immunity, for COVID, or for any other respiratory infection.