Jeg har tidligere skrevet om betydningen af sen vinterferie her. Men i dag vil jeg gerne fremhæve centrale afsnit og konklusioner fra Arnarson (2021) og Björk et al. (2020).
I forhold til København, blev Stockholm ramt ca. dobbelt så hård, alene fordi vinterferien lå på et andet tidspunkt, mens ca. 38% af overdødeligheden kan forklares af denne tilfældighed.
We can see that the initial impact is strongest in regions with a school-break in week 9 (over 90%) [higher spread] secondly in week 10 (50-95%) and lowest in week 8 (35%). As before these results are relative to regions that had a break in week 7 or before.
Arnarson (2021)
Being a region with winter holiday exclusively in week 9 was in the adjusted analysis associated with 16 weekly excess deaths (95% confidence interval 13 to 20) per million inhabitants, which corresponds to 38% of the excess mortality during the study period in these regions.
Björk et al. (2020)
Arnarson (2021) har også en fin forklaring af, hvorfor dette sker.
Hence, a traveler in week 6, 7, 8 or 9 would only see a limited number of confirmed cases prior to travel (in weeks 5, 6, 7 and 8) but the likelihood of being exposed to Covid-19 would be vastly different. Unaware individuals traveling in the high-exposure week 9 are therefore likely to have been a human transport of Covid-19 to their local area. During the short time window around week 9, the risk of being exposed to Covid-19 during travel was high while the perceived risk was low. As the awareness of the risks was still rather low on return, these individuals are in addition likely to have started their normal lives before the seriousness of the spread was apparent across Europe, amplifying the local geographic exposure.
Arnarson (2021)
Og (måske ikke super overraskende), finder Björk et al. (2020), at tidligere fornuftige anbefalinger virkede ret godt. Bemærk, at ingen lande var over stringency index 35 i uge 11, hvilket basalt set betyder, at de på det tidspunkt fulgte myndighedernes anbefalinger og anvendte anbefalinger/information og ikke deciderede nedlukninger, som først kom på bordet senere, da politikerne greb ind.
A more stringent response implemented in week 11, corresponding to 10 additional
Björk et al. (2020)
units on the 0-100 ordinal scale, was associated with 20 fewer weekly deaths (95% confidence interval 18 to 22) per million inhabitants.
Sen vinterferie er blot én af de 16 mulige forklaringer, som Klein et. al (2020) pegede på, som mulige forklaringer på Sveriges høje overdødelig i forhold til andre nordiske lande. Hvor vigtige de andre er, har jeg ikke set undersøgt grundigt, men læren af vinterferie-tesen er, at vi aldrig må undervurdere betydningen af tilfældigheder.