Governments follow different approaches when it comes to tackling viral pandemics. One controversial way is to allow for herd immunity, which is a form of indirect protection from infections that occurs when a large percentage of the population has become immune to infection through previous exposure, thereby protecting non-immune individuals [29]. Supporters of this opinion believe that lockdown does not prevent the spread of viruses; it only delays the inevitable spread at the cost of severe social and economic losses. On the other hand, many argue that lockdowns decrease the reproduction number, which is the average number of secondary cases each case generates, hence decreasing or eliminating human to human transmission, deaths, and burden on the health system [30].
At the beginning of the COVID-19 pandemic, England and Sweden followed the herd immunity approach to control the spread. Ferguson et al. at Imperial College London published a report estimating that 510,000 people would die in the UK without any mitigation [30]. The UK prime minister announced a complete lockdown on March 23, 2020, while Sweden continued with the herd immunity. Table 1 shows the difference between England regulations and Sweden recommendations during the COVID-19 pandemic [31, 32]. To understand the impact of the UK lockdown on COVID-19 spread, we used an ITS and compared England outcomes with Sweden as a control due to lack of lockdown. This design is useful to assess the effect of implemented health policy or in natural experiments [18]. Authors elected to compare only England to Sweden because its health care system is the only one that is accountable to the UK government. Wales, Scotland, and Northern Ireland have their own publicly funded health care systems that are accountable to their governments [33]. Moreover, there is some variation in the health system and policies between the four countries [34]. Although most European countries implemented lockdowns, authors compared the UK to Sweden because of the delayed lockdown in the UK, which led to the rapid spread of the virus in the UK, similar to Sweden in the pre-lockdown phase. The ‘similar’ trends in the pre-lockdown are essential to draw inferential estimates.
Table 1
Comparison of measurements implemented by England and Sweden government to decrease the spread of COVID-19 infection
| England[31] | Sweden[32] |
Stay at home order | -People should only leave or be away from their home for very limited purposes: 1. Shopping for basic necessities, for example, food and medicine, which must be as infrequent as possible. 2. One form of exercise a day, for example, a run, walk or cycle alone or with members of one's household. 3. Any medical need, including to donate blood, avoid injury or illness, escape the risk of harm, or to provide care or to help a vulnerable person. 4. Traveling for work purposes, but only where individuals cannot work from home. | -A ban on visiting all of the nation's care homes for older people has been in place since April 1, 2020. -Maintain social distancing by keeping a distance from each other and refraining from non-essential travel within the country. |
Closing certain businesses and venues | -The government closed the following businesses to the public by law: 1. Pubs, cinemas, and theatres. 2. Clothing and electronics stores; hair, beauty and nail salons, and outdoor and indoor markets (not selling food). 3. Libraries, community centers, and youth centers. 4. Indoor and outdoor leisure facilities such as bowling alleys, arcades, and soft play facilities. 5. Communal places within parks, such as playgrounds, sports courts, and outdoor gyms. 6. Places of worship (except for funerals). 7. Hotels, hostels, bed and breakfasts, campsites, caravan parks, and boarding houses for commercial/leisure use, excluding the use by those who live in them permanently and those who are unable to return home | - All venues must ensure that tables are spaced appropriately to avoid crowding. - People must always be seated when consuming any food or beverages. |
Stopping public gatherings | - Public gatherings of more than two people are prohibited. | - Ban public gatherings of > 500 people, this was lowered to 50 people on March 29, 2020. - Upper secondary school and University education are conducted online, but preschools and elementary schools remained open. |
Going to work | -People are allowed to travel for work purposes, including to provide voluntary or charitable services, where work from home is impossible. | - No specific recommendations, people were encouraged to refrain from non-essential travel. |
Enforcing the law | -The police and local authorities have the power to enforce the requirements set out in law if people do not comply with them. If people breach these regulations, the police may: - Instruct people to go home, leave an area, or disperse. - Instruct people to take steps to stop their children from breaking these rules if they have already done so. -Take an individual home or arrest an individual, where they believe it is necessary. | - The only recommendation that was subject to the penalty was banning public gatherings of more than 50; otherwise, everything else was a non-enforceable recommendation |
Use of personal protective equipment including masks | - No recommendations. - Start mandatory masks on public transportation on June 15, 2020. | -No recommendations. |
The estimated causal effect is the result of net anti-COVID-19 measurements implemented by England but not Sweden (Table 1). During the pre-lockdown phase, the COVID-19 epidemic was spreading at a higher rate in England than Sweden. The enhanced spread resulted in higher COVID-19 related mortality. After lockdown implementation, the rate of daily COVID 19 cases decreased in England in comparison to Sweden. The decline in daily confirmed cases rate after lockdown compared to pre-lockdown is estimated to be 19 fewer cases/ 10,000,000 person. Because COVID-19 cases dropped in England, both countries' curves crossed over during May 2020 (Fig. 1). Moreover, the daily COVID-19 mortality rate decreased by two deaths/10,000,000 in England compared to Sweden.
To prevent a rebound increase in COVID-19 spread, the UK used a planned timetable to lift restrictions using three phases [35]. Phase one started on May 13. During phase one, more people were allowed to go to work if needed, and to drive to outdoor spaces irrespective of the distance. Also, outdoor exercise time was increased. Phase two started on June 1. Children were able to return to early years setting, and for Reception. Year one and year six were allowed back to school in a smaller size. Non-essential retail stores were allowed to open gradually. More local transport in urban areas was allowed to open. Sporting events can take place behind closed doors. People were allowed to expand their household groups to include one other household. This gradual reopening was always associated with reinforcement of social distancing, wearing face-covering, and frequent handwashing. In this study, the trends of daily COVID-19 cases and related deaths did not increase in England compared to Sweden with phases one and two of lifting restrictions (eTable 2). Authors believe that this cautious, gradual reopening, in addition to people's compliance with regulations, explains the absence of a second surge so far. Phase three started on July 4. However, the authors did not estimate COVID-19 daily cases and deaths in this phase.
Interrupted time-series analyses are difficult to interpret when outcomes follow a nonlinear relation. Commonly, epidemics grow exponentially, slow down, and then decay exponentially [36, 37]. This "natural evolution" was not seen universally in the COVID-19 pandemic. The authors used a comparative model to control for the complex and dynamic growth of the COVID-19 pandemic. Another method to estimate a health policy effect is to use difference-in-difference method [38]. Authors used comparative interrupted time series analysis because it was unclear if both countries would follow a parallel trend in the future and because interrupted time series allows for more complex time trends using nonlinear models [38, 39]. In addition to that, comparative time series analysis can adjust for non-parallel trends between groups and allows for time-varying confounders [39].
Innate to non-randomized designs, our study has some limitations. England and Sweden are geographically separated, hence other confounders or co-interventions may have affected the outcomes. Time-varying confounders, including seasonality, can threaten the internal validity of ITS analysis. Authors believe this is unlikely due to several reasons. Both countries used similar tools to measure outcomes [19, 21]. Second, England and Sweden have a comparable life expectancy (80.8 vs. 81.1 years, respectively) suggestive of similar health quality [40]. Lastly, the COVID-19 pandemic started at the same time in both counties. This study only addresses short-term outcomes of lockdown order; the authors analyzed data of the first 100 days post-lockdown. Long-term trends in COVID-19 infection were not addressed and may increase after phase 3 of lockdown loosening in England.
In conclusion, the lockdown implemented in England did result in a statistically and epidemiologically significant reduction in the COVID-19 daily new cases rate compared to Sweden. The decline in daily cases also resulted in a drop in daily death rate related to COVID-19 in England. Lockdown in England has successfully halted COVID-19 transmission in the short-term. However, long term outcomes are unknown, and a new epidemic during winter is possible. Future research is needed to understand the long-term net outcome of the anti-COVID-19 policy implemented in both countries.