German R Number Has “No Direct Connection” With Lockdown, Say Researchers

Since the start of the pandemic, Germany has seen the lowest level of excess mortality of any major European country – just 4% according to the World Mortality Dataset. Is this because the country effectively suppressed the virus using lockdowns? A new research note suggests not.

Annika Hoyer, Lara Rad and Ralph Brinks – three researchers at the Ludwig Maximilian University of Munich – sought to compare the epidemic’s trajectory to the timing of lockdown measures. (Their paper is written in German, but you can translate it using Google.)

Hoyer and colleagues begin by noting that, due to changes in testing, case numbers are unsatisfactory for tracing the epidemic over time. They note, “Varying test behaviour should be understood here as the fact that in the course of the epidemic… the execution of tests has changed and changed very strongly, both temporally and regionally.”

They argue that the R number (the average number of people an infected individual transmits the virus to) provides a better guide to the epidemic’s trajectory. According to the authors, “The estimation of the R-value also involves some statistical difficulties, such as the necessary nowcasting, but the main disadvantage of the dependency on test behavior, which can imply large fluctuations, does not apply.”

Hence they plotted the R number over time, and looked for major changes or “breaks” in the series – as shown in the chart below:

The R number decreased dramatically in March of 2020. It rose slowly over the following six months (the apparent spike in the summer may be a random fluctuation due to the small number of cases at the time). It then rose more quickly in September, only to fall again in October. It fluctuated around 1 during the winter months, and has fallen since the start of April.

Given that Germany’s first lockdowns (which varied from state to state) were imposed around March 22nd, it’s clear that the initial decline in infections preceded them. (The statistician Simon Wood has argued that the same thing happened in Britain – i.e., infections were already declining when lockdowns came into force.)

Hoyer and colleagues point out that changes in the R number don’t seem to be correlated with the timing of winter lockdowns either. They note, “there has been no direct connection with the measures taken since September – neither with the lockdown light on November 2nd and the tightening on December 16, 2020, still with the ‘Federal Emergency Brake’, which was decided at the end of April 2021”.

Their research note provides further evidence that lockdowns have little impact on the epidemic’s trajectory beyond the effects of voluntary social distancing and restrictions on large gatherings.