The common factor around the globe that caused the dramatic reduction in Covid cases from around April isn't 'the jets'. Consider instead lockdowns, social distancing, contact tracing, etc. Go to the link below, and press the play button. This will show you the extent to which each nation took action to prevent the spread, and when they took action. Compare your findings to the other charts on that site, including the one in the post you quoted. You can even download the source data.


https://ourworldindata.org/policy-responses-covid