This is not a topic that I have researched but I do look at studies if they comes my way. None have until recently when I received the following paper by van den Berg et al.
This was a very large study of students and staff in Massachusetts public schools totalling 6.4 million student learning weeks and 1.3 million staff learning weeks. In particular, it covered two groups of schools, one in districts with ≥3 feet of physical distancing rules, and one with ≥6 feet rules. For each group, it examined two cohorts, one of students and one of staff. It looked at COVID-19 “incidence rates” (case numbers) as well as community incidence rates as an adjustment, to develop a case model. “Incidence case ratios” (IRR) between the cohorts in the two distancing regimes were calculated.
An IRR of 1.0 means that a cohort in one group has identical results with its corresponding cohort in the other group. Although scientific experiment and model results are expressed as a single value, in fact the value has an error range or confidence interval (CI) associated with it. Thus, when you see a result written as “(IRR, 0.891, 95% CI, 0.594-1.335)”, it means that, since 1.0, the value indicating the two cohorts have identical results, is well within the CI of the model value’s CI for 95% probability, the difference between the two is “statistically insignificance”. The authors phrase this as both cohorts were “similar“.
As the authors conclude:
There is no significant difference in K-12 student and staff SARS-CoV-2 case rates in Massachusetts public school districts that implemented ≥3 feet versus ≥6 feet of physical distancing between students, provided other mitigation measures, such as universal masking, are implemented.
Lower physical distancing policies can be adopted in school settings with masking mandates without negatively impacting student or staff safety.van den Berg et ai (2021).
Note that the study did not study the overall effectiveness of social distancing (SD) as an NPI (non-pharmaceutical intervention) technique. Consider that the population in general practices SD as a matter of innate behaviour. When we (in the West) talk to another we stand no closer than about 18 inches (1.5 feet) apart.
So if an SD of 6 offers no additional benefit over an SD of 3 (that’s all the study proves), one may rightly ask how much of a benefit an SD of 3 offers over and SD of 1.5? The study has yet to be done but one might conjecture that any SD over the normal one practised innately offers no additional benefit. Another way of posing the conjecture is “what difference can a foot and a half make?” This leads to the conjecture that additional SD rules are not measurably effective.
The problem with NPI assessment in general is that it is a multivariate problem. That is, there are a number of distinct NPIs that we use, each of which becomes a variable in any analysis. This does not mean that they are independent of each other but we usually, for simplicity, assume independence. The standard approach to analysis of problems of this nature is to assume that all variables except one can be fixed. Then under this condition, the remaining variable is analyzed over a range of values to produce a result.
The authors state the condition that masking mandates and other NPIs remain in place to inform their results. This is not to be interpreted that their results are valid only if a masking mandate is in effect. Such a mandate is a separate NPI variable and this experiment does not examine the effectiveness or not of such a mandate.
One last point that I wish to address is the use of young children to evaluate SD rules. Some may argue that the experiment does not apply to adults. A primary difference between children and adults is that they appear to be less infectious. SD can be considered to be a parameter of disease transmission. Infectiousness can be also. By comparing like cohorts, children to children and not children to adults, we fix the value of this variable and it is removed from the problem. In fact, this is true for all parameters that are different between adults and children. The conclusions about SD rules apply to all age groups. Also, observe that the conclusions apply directly to the adult cohort of the study.
- van den Berg P, Schechter-Perkins EM, Jack RS, et al. Effectiveness of three versus six feet of physical distancing for controlling spread of COVID-19 among primary and secondary students and staff: A retrospective, state-wide cohort study. Clinical Infectious Diseases, 2021;, ciab230, https://doi.org/10.1093/cid/ciab230. PDF.