Corona: Vacation Season Effect on Infections (Germany)

Do you wonder if traveling and vacation season has some effect on Corona spread? German numbers suggest it has – and it can be seen in new cases.

German Corona Infections for three fedaral states.
New Corona Infections (7 day incidence) of three German federal states. The red lines show a state with early school holidays, whereas the blue and green plot show two states where summer break is late. (Plot: Rainer Gerhards, Data: RKI)

Rise and Fall of Corona with the Vacation Season

There seems to be a strong relation between summer school break and Corona spread. Above chart, based on Government-provided data, shows three of Germany’s federal states. Federal states over here start summer break at different times, some do it early, some do it later. By now, almost all states are back to school, with the exception of the two shown in blue and green (it’s another 10 days to go).

Interesting fact: the red line begins to climb approximately 14 days after school holiday season begins. More interestingly, it begins to decline … approximately 14 days after holiday season end. The other two state keep stable until both of them begin to climb. That happened approximately 14 days after begin of their holiday season.

Their ascent, however, has mostly stopped for the past 10 days, while still in holiday season. My explanation is that measures taken by the Government caused this. We declared some popular vacation targets with high case numbers as so called “high risk regions”. In essence, this means it makes traveling to them harder, even though it is not forbidden. If you look at other German federal states, you find a similar pattern. Infections have risen during the vacation season and stop thereafter.

Why does Corona rise during Vacation time?

Of course, simple answers are always a bit dangerous. But a bit of common sense and experience tells us that during vacation time

  • people obviously travel larger distances – some within the country, some within Europe (the volume outside of Europe was very low this year, of course). Long exposure in confined spaces like Airplanes and trains bear a bit higher infection risk per se.
  • during vacation, most people are a bit more relaxed and less careful – even if they are very Corona-sensitive at home
  • some people who do not think Corona is a serious illness, travel to destinations with (very) relaxed rules to do all these things that help spread the virus (like parties). News report for sure tell us that this happened. Most new cases “imported” to Germany are from such destinations.

Summing this up, everyday experience and news reports match the numbers. So I conclude that there is a correlation. If there is, it also tells us where additional risk is and how we can avoid it. After all, that’s the main point of why this information might be useful to someone.

Coincidence or Correlation?

Still, you may think it is pure coincidence (or at least of lot of it). Well, I am not qualified enough to provide a firm answer. But the change looks statistically significant and so I would rule out the development, and it’s precise timing, to be pure coincidence. Also, the overall conditions in Germany did not see any drastic change during that period. Some people argue the strongly increased number of Covid-19 testing has produced access false positives. However, this theory does not explain why the case numbers have at times risen sharply e.g. for the blue line while testing was increased only moderately (data available upon request – or visit the official German source). Also, while the specificity of the standard rt-PCR SARS-CoV-2 test leaves a 1% false positive margin, lab processing, at least in Germany, usually reduces this to 0.04% (German Newspaper Report)

Why am I writing about Corona? Am I qualified?

Corona and Covid-19 is not my usual blogging topic here on my English blog. However, I participate in many discussions on twitter and elsewhere and, by popular demand, I thought I share a quick English post on the Corona new infections and the summer break season.

As you know, I am not a doctor nor do I have any specific qualification in medicine in this regard. But I know how to do my statistics and how to correlate events. Also, I track Corona constantly for my German blog and do so because I am a councilman in my home village. We need the best local data we can get hold of to fight Corona.

So while I am not an expert and the Corona pandemic at all, I am a bit better informed then, well, a couple of other folks.

I hope this blog post is useful. Be sure to look critical at it and use your own judgement, hopefully based on solid numbers and science. All readers please stay healthy!