Evidence for Interventions

Physical Interventions – Social distancing, Lockdowns, Isolation,Quarantine and Mask Mandates.

On what basis these measures were introduced has been a source of discussion and debate. What is the evidence for the effectiveness of these interventions one year after their introduction?

Social Distancing

A study published in 2020 from Cochrane Collaboration reported that all evidence for the practice of keeping distance associated with covid-19 related disease and mortality comes from modeling studies. Four observational studies focused on severe acute respiratory syndrome and Middle Eastern respiratory syndrome. The UK Department of Health also highlighted the lack of good data on the effectiveness of these measures against influenza.
In a larger study across 149 countries, interrupted time series analysis were used to compare the change in the incidence of covid-19 before and after implementation of interventions with physical distancing as the goal. In this study, tables with confidence intervals show that there is no evidence that such systematic measures generally have any significant effect.


In late summer, a new mutation of the SARS-CoV2 virus was discovered among mink farms in Denmark. Researchers from the Danish Serum Institute warned against the mutation, and politicians demanded action. On 4 November, the Prime Minister announced that in the Danish region of North Jutland, seven municipalities would go into a “lockdown” corresponding to the red level with homework, closure of commercial and leisure activities and closure of public transport.

A total of 280,000 people and 126,000 jobs were affected by the extreme restrictions, as people were banned from crossing municipal boundaries to go to work. Restrictions were implemented in seven municipalities. Spread among these municipalities, all in the same region of North Jutland, were four municipalities that did not follow these restrictions; they remained under the moderate advice given to the inhabitants of the rest of Denmark. Here was a golden opportunity to compare the effect between such very strict restrictions with municipalities that had not introduced such strict restrictions but which were basically very similar in terms of geography, language and culture.

Here we have two population cohorts that can be compared. The endpoint measure of efficacy in the study was new infection cases measured by SARS-CoV-2 RT-PCR and where one shifted by 4, 7 or 10 days to allow an uncertain incubation period for the virus. During the seven days before the lockdown, this cohort had 1.5% positive tests per day compared with 1.4% in the “no lockdown” cohort. Later in the spring, the “lockdown” group registered a total of 6.9% positive tests per thousand inhabitants, while the “no lockdown” group registered 8.2% positive tests (not significant differences). Thus, no statistically significant differences were found between the two municipal groups either before or after the intervention. The similarity in the number of new infections before the intervention meant that this could be said to be in fact a so-called “quasi-natural experiment”.

As shown below the number of Covid infections in the two groups was already declining before the major restrictions in the “lockdown” municipalities began – and they continue to fall equally in both groups with a conclusion that these restrictions cannot be seen to have affected further spread.

Reported infection levels

Lockdowns Don’t Prevent Coronavirus Spread

Comparisons test positive between study groups

Lockdown Effects on Sars-CoV-2 Transmission – The evidence from Northern Jutland
Mask Mandates

A search of the so-called University of Oxford “COVID test tracker” in July 2020 found nine registered studies that dealt with the importance of using face masks, of which six recruited participants. Two studies on the use of face masks are worth commenting on.

In Denmark, a randomized study was conducted with 6000 participants –Danmask-19 – to be able to say something about the effect of using surgical face masks with a view to reducing the risk of COVID-19 infection outside the health care system. In Guinea-Bissau in West Africa, the leader of the Bandim Health Project, a randomized trial of 40,000 participants using cloth face masks has been launched.

Covid-19 is now perceived as an airborne disease and it is on that basis that orders have been issued with the use of face masks. However, the “DANMASK-19 Study” showed that surgical face masks have limited air filtration capacity with respect to SARS-CoV-2 and have no real effect in preventing infection. In the Denmark study, the number with SARS-CoV-2 infection was measured in those who used the mask compared with those who did not use the mask one month after the study was started. The target used as the primary endpoint assay was a positive SARS-CoV-2 RT-PCR test or hospital diagnosis on Covid-19. Secondary endpoint targets were PCR positivity for other respiratory viruses.

A total of 3030 participants received a recommendation to use masks, and 2994 were recommended not to use masks as a control; 4862 completed the study. Infection with SARS-CoV-2 was registered in 42 participants who received recommended masks (1.8%) and 53 control participants (2.1%). The difference between the groups was -0.3 percentage points (95% CI, -1.2 to 0.4 percentage points; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.33). Several corrections for the loss of participants in follow-up gave similar results.

The conclusion of this study is that in a society with a modest infection rate, there is little basis for the recommendation to use surgical masks to supplement other measures.

Another conclusion from the study comes from the interpretation of the frequency of infection.

Thanks to the DANMASK-19 study, Denmark is the only country in the world that now has reliable estimates from both the first and the second epidemic wave. The study was conducted just after the first wave where 2% PCR positive tests were recorded “infection” per month which was similar to the second wave that came in October to November in 2020. It further confirms that all measures taken in Denmark to preventing a new wave could have no concrete effect on the spread of Covid-19 included a universal injunction with the use of masks.

Combination of interventions

A combination of school closure, closure of workplaces and restrictions on mass gatherings with or without closure of public transport were in some studies associated with a minor reduction in the incidence of covid-19 but only three out of ten studies could show any real statistically significant evidence of very small effect size. A combination of several measures thus shows a small but insignificant and uncertain effect.

Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries

The conclusion that one can draw is that there is no real association between the occurrence of covid-19 and any or combinations of measures that have been implemented in Nordic Countries.

NB! It is important to note that the studies here suffer, like all other studies , around the uncertainty surrounding the PCR tests if these are used for measuring disease due to lack of gold standard.