Actually, I do know it to be true. I used the case data and conducted the analyses myself, according to the known principles of infectious disease transmission.
Believing that the mitigation measures have had no effect on the spread of Covid-19 is like believing that measles spontaneously disappeared, rather than recognizing the role of vaccines in getting rid of measles. Preventive measures work!
Vaccines work. Check Sweden and South Dakota for efficacy of “mitigation” vs reality.