My prepared talk at last night’s Emergent Response Policies roundtable:

Germany discusses instituting a Case-Fatality Rate instead of general 7-day incidence per 100’000 to decide on further measures. A good move, in my opinion, but not one that will calm either side of the denier/panic debate. With vaccinations reaching 40%+ in many countries, the initial impetus for instituted lockdowns and mask mandates, the need to take strain off the health care system, must be revisited.

The German “Intensivregister” (in German) shows steadily declining cases of ventilated and non-ventilated patients, despite a rise in infections and the rapid emergence of the Delta variant in Europe.

Understanding, that masks are at best infection speed bumps and that only restrictions on event and gathering sizes as well as vaccinations have any hope at curbing health care overload for good, more must be done to educate and inform those who are either misguided about the mechanics and dangers of a vaccination or are on the fence due to other reasons.

We also must put much more effort into ensuring it is understood, that these vaccines do not prevent anyone from becoming infected or infecting others1 but are valuable and needed tools to greatly reduce the incidence of moderate to severe COVID-19, Long COVID, and death in those who are infected. Given the current strains, widespread vaccination coverage could ensure a drop below Influenza morbidity and mortality numbers.

Our current modeling shows a significant drop at 40, 56, 68, and 73 percent vaccinated adults and adolescents above the age of 16 if social distancing rules are maintained below a rate of 56% vaccinated (no large2 public events) and mask requirements are maintained until a full dose +14 day vaccination rate of 68% has been reached. Outdoor mask requirements do not, in observational studies and one review, show much of a reduction in spread but might be useful for other reasons. It has also been shown that even “made unusable” FFP2 masks (e.g. having been cleaned, reused, or used for periods of time exceeding manufacturer specifications) can contribute significantly to pandemic spread reduction3.

Masks show a “small to moderate” effect on individual infection rates per eCDC, but provide a much larger effect on pandemic control.

This is well stated in a study by Howard et al:

By contrast, the effect of masks on a pandemic is a population-level outcome where individual-level interventions have an aggregate effect on their community as a system.

In other words, masks in a pandemic behave like highway tortoises (slow drivers in the fast lane): the act of slow driving does not in itself impart a significant effect upon the driver or the cars following directly behind. A chain effect, modellable in in a fluid dynamics simulation, however, shows increasing effects on cars following the initial cohort, down to a predictable traffic jam and total gridlock up to 45 minutes past the initial slow down event.

Masks and social distancing remain therefore important tools in source control (making sure infected and vaccinated individuals do not infect unvaccinated individuals) and pandemic control (“breaking the chain,” slowing the viral spread).

It is, however, imperative to switch our view from overall infection rates to infective events requiring medical intervention and hospitalization, including death, to model further responses. Rather than being the determining factor in response modeling, seven day incidence per 100’000 should become an important factor but not the driving model.

  1. The much decreased time-in-host for vaccinated carriers of SARS-CoV-2 does contribute statistically significant to a reduction in infection rates. However, the belief that vaccinations fully prevent infections or transmission might negatively impact this, as those who are fully vaccinated begin to enjoy additional freedoms or assume they are no longer at risk for either. [return]
  2. The value for “large” has been debated ad absurdum. For the regression model we assumed “large” to mean gatherings of 20 and more people without mandatory SARS-CoV-2 testing prior to meeting. [return]
  3. But it should be clear, that reusing FFP masks, cleaning them, or wearing them (link in German) beyond the (generally 8h) time limit does render them functionally incapable of performing most protective measures. [return]
Mikka Luster @mikka