A statistically significant difference doesn't say anything about the magnitude of the difference. It means, statistically, we believe there to be a difference. Typically if we are 95% sure that there is a difference, then we say it is statistically significant.

For the sake of argument, if wearing a t-shirt over your face reduces your chances of getting the virus by .01%, but we were 99% sure that was true, it would be a statistically significant difference. If they reduced your chances of getting the virus by 10%, but you were only 80% sure, that would not be a significant difference.