I wonder if the “normal” social distance kept by various cultures has a bearing on transmission, especially before extraordinary measures became common. In 2017, the Washington Post had an article on cultural differences in personal space. The article is pay-walled; I have linked it for subscribers. It shows that personal distance is remarkably lower in Italy than in South Korea, especially for family members and close friends. (I don’t say “significantly lower,” because that’s the question.) In addition, Italians often greet each other with air kisses where east Asians do not. Many African and west Asian men hold hands as a sign of friendship. During the period when the existence of a bug is unknown or doubted, such things would be expected to affect transmission rates.