Table 1 Characteristics of included studies and main outcomes

Pan A et al [14], China

Interrupted

time series

Evaluate the association of several public health interventions on the control of COVID 19 outbreak over 5 periods according to key interventions.

32, 583 laboratory-confirmed COVID-19 cases. Time periods and Interventions: 1st period: time before January 10, 2020 without specific intervention. 2nd period: January 10 to 22, 2020, no strong intervention, massive migration, first human-to-human transmission on January 20 and hospitals started to be crowded.3rd period: between January 23 and February 1, 2020 city lockdown, traffic suspension, home quarantine, social distancing measures including compulsory mask wearing in public places and cancellation of social gatherings.4th period: February 2 to 16, 2020 intensified measures with centralized quarantine and treatment, improved medical resources and stay at home policy.5th period: February 17th to March 8th 2020, centralized quarantine and community universal survey. Rt: effective reproduction number is the mean number of secondary cases generated by typical case at primary case is an indicator that measures SARS-CoV-2 before and after the intervention.

The daily confirmed case rate per million people increased from 2.0 (95% CI, 1.8–2.1) before January 10, to 45.9 (95% CI, 44.6–47.1) in the 2nd period, to 162.6 (95% CI, 159.9–165.3) in the 3rd period and then decreased to 77.9 (95% CI, 76.3–79.4) in the 4th period. After February 16, it decreased to 17.2 (95% CI, 16.6–17.8). Rt varied in the first period, gradually increased in the 2nd period with a peak of 3.82 on January 24, and then declined. It fell below 1.0 on February 6, 2020, and further decreased to below 0.3 on March 1, 2020.

Wang K-W et

al [15], China

Interrupted

time series

Estimate the effects of wartime control measures after early imported COVID-19 cases in Jiangsu from Hubei

Province.

Time series observations from January 2 2 to February 18, 2020. Wartime control measures: Collect estimate, report and release emergency information every day. Put cities with epidemic on lockdown to limit population mobility. Restrict or stop crowd gathering. Migrant management such as on-site isolation for confirmed COVID-19 cases and contact tracing. Traffic health quarantine.

From January 22to February 18, 2020 the number of confirmed cases increased from 1 to 631. No new confirmed cases were identified after February 18th.

Cowling BJ et al [16], Hong Kong

Cohort Study

Quantify behavioural changes in population of Hong Kong during the COVID-19 outbreak and describe effect of public health interventions on COVID-19 and influenza transmission.

Public health interventions: Travel and border entry restrictions and bans, testing, tracing, flexible working arrangements, school closures, quarantine and isolation orders that has been issued for cases and their contacts and travellers arriving from affected countries, cancellation of many conferences, some religious organizations and local mass gatherings and social distancing. Rt: effective reproduction number, mean number of secondary infections that result from a primary case of infection at time t.

Public health interventions and population behaviour changes such social distancing and personal protective measures implemented in Hong Kong since January 2020 is associated with reduced spread of COVID-19. Contact tracing, quarantine and social distancing played an important role in suppressing transmission adding to case identification with isolation.

Jüni P et al [17], 144 geopolitical areas

Cohort

Study

Determine whether epidemic growth is associated with climate or public health interventions.

Prospective cohort study of 144 geopolitical areas with at least 10 cases and local transmission excluding China, South Korea, Iran and Italy. Determination of the association between epidemic growth and latitude, temperature, humidity, school closures, restrictions of mass gatherings and measures of social distancing during an exposure period from March 7 to 13, 2020) using weighted random-effects regression.

Few or no associations of epidemic growth with latitude and temperature, weak negative association with relative and absolute humidity. Strong associations for implemented public health interventions.

Wang J et al [18], China

Longitudinal Study

Estimate the incidence of 2019nCoV infection among people who are under home quarantine in Shenzhen province, China.

Stratified multistage random sampling method has been used to recruit participants and collect demographic information and laboratory results of people under home quarantine. Descriptive analysis was conducted to estimate the basic characteristics and to calculate the Incidence of novel coronavirus (2019-nCoV) infection among people under home quarantine. In order to report the outcomes of categorical variables proportions and frequencies were used. Mean and range were used to express continuous variables.

Testing for a total of 2004 people was conducted and three of these tested positive for 2019nCoV.The incidence of COVID-19 in the sample was 1.5‰ (95% CI: 0.31‰–4.37‰). None of the three patients had obvious symptoms during the time of home quarantine. Also, they did not report any history of contacts with confirmed cases. Home quarantine has been effective in preventing the early transmission of COVID-19.

Cheng VC-C et al [19], China

Cohort Study

Assess the effect of community-wide mask usage to control COVID-19 in Hong Kong Special Administrative Region (HKSAR). Analyze the incidence of COVID19 in geographical areas with or without community-wide masking.

During the first 100 days epidemiological analysis was performed for confirmed cases especially the ones that acquired COVID-19 during mask-off and mask-on settings. The incidence of COVID-19 per million populations in HKSAR with community-wide masking was compared to that of non-mask- wearing countries which are comparable with HKSAR in terms of population density, healthcare system, BCG vaccination and social distancing measures but not community-wide masking.

Epidemiological measures by the HKSAR government: border controls from day 36, followed by imposing home quarantine order for 14 days to all entrees from mainland China from day 40. Then, the quarantine order was progressively imposed to all entrees into HKSAR from day 80. All entrees were compulsorily tested for SARS-CoV-2 from day 100. In addition to isolation of confirmed cases, contact tracing and quarantine, closure of affected or high risk premises, and social distancing measures such as home-office and school closure were instituted. 961 cases of COVID-19 were confirmed in HKSAR on day 100. From day 31 to 71 there were 111 cases predominantly local cases and from day 72 there were 840 cases predominantly imported cases with local clusters of cases. Among the 961 confirmed cases, there were 11 clusters of 113 persons that were directly engaged in mask-off activities. There were only three clusters involving 11 persons engaged in mask-on settings at the workplace there were significantly more COVID-19 clusters involving mask-off settings.

Thu TPB et al [20], The U.S., Spain, Italy, The U. K, France, Germany, Russia, Turkey, Iran and China.

Longitudinal Study

Present the effect of social distancing interventions on the spread of COVID-19 in the cases of 10 highly infected countries.

The relationships between the social distancing interventions and the statistics of COVID-19 confirmed-cases and deaths were analyzed in order to elucidate the effectiveness of the social distancing interventions on the spread of COVID-19 in 10 highly infected countries including The U.S., Spain, Italy, The U.K., France, Germany, Russia, Turkey, Iran and China.

It took between 1 to 4 weeks since the point of highest level of social distancing measures promulgation until the numbers of daily confirmed-cases and daily deaths showed signs of decreasing. The effectiveness of the social distancing measures on the spread of COVID-19 was different between the 10 studied countries. This variation is due to the difference in the level of promulgated social distancing measures and in the difference in the COVID-19 spread situation at the time of promulgation in these countries. The growth rate of daily confirmed-cases at the time of promulgating the social distancing measures partly influences the decline rates of daily confirmed-cases after the spread reached its peak.

Seong H et al [21], South Korea

Cohort Study

Compare the epidemiologic features of the second and third waves of the coronavirus disease

2019 (COVID-19) pandemic in South Korea.

COVID-19 data were collected between 6 May and 30 December 2020. The degree of social activity was estimated using an Internet search trend analysis program for leisure-related keywords, including ‘eating-out’, ‘trip’ and ‘get directions’ (transportation). Demographics, transmission chains, case fatality rates, social activity levels and public health responses were compared between the second (13 August–18 September 2020) and third (4 November 2020–present) waves.

The 3rd wave was characterized by delayed strengthening of social distancing measures (3 vs.15 days), longer duration (36 vs. > 56 days) and a higher case fatality rate (0.91% vs.1.26%) compared to the 2nd WAVE. There were significant differences in transmission chains between the two waves (P < 0.01). In comparison with the second wave, the proportion of local clusters (24.8% vs. 45.7%) was lower in the third wave, and personal contact transmission (38.5% vs. 25.9%) and unknown routes of transmission (23.5% vs. 20.8%) were higher in the third wave. In conclusion early and timely interventions with strengthened social distancing policies should be implemented to suppress and control the COVID-19 pandemic effectively.

Lam HY et al [22], Hong Kong

Longitudinal Study

Review the epidemiology of the

confirmed COVID-19 cases reported between January to May 2020

Assess the overall effectiveness of the various public health

Interventions.

Description and comparison of the epidemiological and clinical characteristics of the cases recorded in different phases of the epidemic. Using the changes in the daily number of confirmed cases and the interval from symptom onset to hospital admission the effectiveness of the public health interventions implemented were reviewed.

Several public health interventions such as enhanced surveillance, border control, and social distancing, were introduced in phases in response to the rapid spread of the coronavirus locally and globally. Overall, the combination of public health interventions taken in Hong Kong were associated with a stabilization of case numbers and absence of a community-wide COVID-19 outbreak during the 4.5 m following the reporting of the first case.

Salvatore M et al [23], India

Longitudinal Study

Evaluate the effect of four-phase national

lockdown from March 25 to May 31 in response to the

COVID-19 pandemic in India.

Participants Confirmed COVID-19 cases nationally and across 20 states that accounted for > 99% of the current cumulative case counts in India until 31 May 2020. Exposure Lockdown (non-medical intervention).

Results The estimated effective reproduction number R for India was 3.36 (95% CI 3.03 to 3.71) on 24 March, whereas the average of estimates from 25 May to 31 May stands at 1.27 (95% CI 1.26 to 1.28). Patterns of change over lockdown periods indicate the lockdown has been partly effective in slowing the spread of the virus at the national level. However, there exist large state-level variations and identifying these variations can help in both understanding the dynamics of the pandemic and formulating effective public health interventions.

Meo SA et al [24], 27 countries

Cohort Study

Assess the impact of 15 days before, 15 days during, and 15 days after the lockdown on the the prevalence and mortality rate in 27 countries during COVID-19 pandemic.

27 countries were randomly selected and the information on the trends in the prevalence and mortality due to COVID-19 pandemic in was taken from World Health. Organization and lockdown data were obtained from studied countries and their ministries. Analysis of the impact of lockdown for 15 days before, 15 days during, and 15 days after the lockdown on the prevalence and mortality due to the COVID-19 pandemic in 27 countries.

Daily cases of SARS-COV-2 and the growth factor results declined and the growth rate per day both declined to an impressive negative level in the case of the growth rate per day by the time period of 15 days after the lockdown period, these two metrics of infection spreading did not fall sufficiently to control the pandemic. Lockdown policies should adhere to optimizing behaviour such as social distancing measures and community wide mask wearing that can affect spreading the COVID-19 pandemic. Lockdown alone will not be effective.

Xu T-L et al [25], China

Longitudinal Study

Summarize the containment measures taken in China, as well as the effect of the practices on SARS-CoV-2 transmission.

The measures taken by the governments was tracked and sorted on a daily basis from the websites of governmental authorities. The measures were reviewed and summarized by categorizations, figures and tables. The population shift levels, daily local new diagnosed cases, daily mortality and daily local new cured cases were used for measuring the effect of the interventions.

Practices were categorized into active case surveillance, rapid case diagnosis and management, strict follow-up and quarantine of persons with close contacts. Together with these measures, daily local new diagnosed cases, and mortality rates were decreased and the daily local new cured cases were increased in China. China’s practices are effective in controlling transmission of SARS-CoV-2.

Zeng K et al [26], United States, Spain, and Italy, with Taiwan, South Korea, and Singapore

Longitudinal study

Compare the measures taken against the spread of COVID-19 in the United States, Spain, and Italy, with Taiwan, South Korea, and Singapore, especially related to the use of digital tools for contact tracing.

COVID-19 death rate information were taken from the European Centre for Disease Prevention and Control (ECDC), accessed through the Our World in Data database and were evaluated based on population size per 100,000 people from December

31, 2019, to September 6, 2020. All policies and interventions were obtained from their respective governmental websites.

Strong association between lower death rates per capita and countries that implemented early mask use and strict border control measures that included mandatory quarantine using digital tools. There was a significant difference in the number of deaths per 100,000 when comparing Taiwan, South Korea, and Singapore with the United States, Spain, and Italy.

These findings suggest that early intervention with the use of digital tools had a strong correlation with the successful containment of COVID-19. Infection rates and subsequent deaths in Italy, Spain, and the United States could have been much lower with early community mask wearing and more importantly timely border control interventions using modern digital tools.

Wong CKH et al [27], 54 countries and 4 epicentres of the COVID-19 pandemic (Wuhan, New York State, Lombardy, and Madrid),

Longitudinal study

Describe and evaluate the impact of national containment interventions and policies such as stay-at-home orders, curfews, and lockdowns on decelerating the increase in daily new cases of COVID-19 rates in 54 countries and

4 epicentres of the pandemic worldwide.

The effective dates of the national containment interventions were reviewed of 54 countries and 4 epicenters of the COVID-19 pandemic (Wuhan, New York State, Lombardy, and Madrid) and cumulative numbers of confirmed COVID-19 cases and daily new cases provided by health authorities were searched. Data were drawn from an open, crowdsourced, daily-updated COVID-19 data set provided by Our World in Data. Moreover the trends in the percent increase in daily new cases from 7 days before to 30 days after the dates on which containment measures went into effect by continent, World Bank income classification, type of containment interventions, effective date of containment interventions and number of confirmed cases on the effective date of the containment measures were examined as well.

122,366 patients with confirmed COVID-19 infection from 54 countries and 24,071 patients from 4 epicentres on the effective dates on which stay-at-home orders, curfews, or lockdowns were implemented from January 23 to April 11, 2020 were included in this study. Stay-at-home, curfew, and lockdown interventions commonly started in countries with approximately 30, 20%, or 10% increases in daily new cases. All three interventions were found to lower the percent increase in daily new cases to < 5 within one month. 20% had an average percent increase in daily new cases of 30–49 over the seven days prior to the implementation of the containment measures; the percent increase in daily new cases in these countries was curbed to 10 and 5 a maximum of 15 days and 23 days after the implementation of containment interventions, respectively. Different national containment interventions were associated with a decrease in daily new cases of confirmed COVID-19 infection. Stay-at-home orders, curfews, and lockdowns curbed the percent increase in daily new cases to < 5 within a month.

Siedner MJ et al [28], USA

Longitudinal study

Estimate the change in COVID-19 case growth before and after implementation of statewide social distancing measures in the US.

The primary exposure was time before (14 days prior to and through 3 days after) versus after (beginning 4 days after, to up to 21 days after) implementation of the first state-wide social distancing interventions. State-wide restrictions on internal movement were examined as a secondary exposure. The COVID-19 case growth rate was the primary outcome. The COVID-19-attributed mortality growth rate was the secondary outcome.

Statewide social distancing interventions were associated with a decrease in the COVID-19 case growth rate that was statistically significant. Statewide social distancing interventions were also associated with a decrease in the COVID-19-attributed mortality growth rate beginning 7 days after implementation; however this decrease was no longer statistically significant by 10 days.

Krishnamachari B et al [29], USA (preprint)

Cohort Study

Examine the effects of government implemented social distancing measures on the cumulative

incidence rates of COVID-19 in the United States on a state level and in the 25 most populated cities

Assessed social distancing variables: days to closing of non-essential business; days to stay home orders;

days to restrictions on gathering, days to restaurant closings and days to school closing. Using negative binomial regression, adjusted rate ratios and 95% confidence intervals were calculated in order to compare two levels of a binary variable: “above median value,” and “median value and below” for days to implementing a social distancing interventions. For city level data, the effects of these social distancing variables were assessed as well in high (above median value) vs low (median value and below) population density cities. For the state level analysis, days to school closing was associated with cumulative incidence, with an adjusted rate ratio of 1.59 (95% CI:1.03,2.44),

p = 0.04 at 35 days.

The effect of social distancing interventions may differ between states and cities and between locations with different population densities. Individual approaches are needed to containment of an epidemic, with an awareness of their own structure in terms of crowding and socio-economic variables.

Singh BB et al [30], India (preprint)

Longitudinal study

Evaluation of the public health interventions using the effective reproduction number (Rt), in key lockdown periods in India.

Laboratory-confirmed COVID-19 infections rates per day and effective reproduction number (Rt) were estimated for 4 periods (Pre-lockdown and Lockdown Phases 1 to 3) according to nationally implemented phased interventions. Adoption of these measures was estimated using Google mobility data. Estimates at the national level and for 12 Indian states most affected by COVID-19 are presented. Using data are publicly available from Google a domain-specific mobility index was constructed using India’s mobility report (Google Inc., Mountain View, CA, USA).

domain-specific mobility index was constructed for the country and 12 Indian states.

Median mobility in India decreased in all contact domains, with the lowest being 21% in retail/recreation (95% CI 13–46%), except home which increased to 129% (95% CI 117–132%) compared to the 100% baseline value.

The Indian government imposed strict contact mitigation, followed by a phased relaxation, which slowed the spread of COVID-19 epidemic progression in India.

Kepp KP et al [31], Denmark (preprint)

Quasi experimental study

Analyse the unique case-controlled epidemiological

dataset arising from the selective lockdown of parts of Northern Denmark, but not others, as a consequence of the spread of mink-related mutations in November 2020.

A quasi-natural experiment in the Danish region of Northern Jutland. 7 of the 11 municipalities of the region went into extreme lockdown in early November after the discovery of mutations of Sars-CoV-2 while the four other municipalities retained the moderate restrictions of the remaining country. Incidentally, the infection numbers in the two groups were compared.

While infection levels decreased, they did so before lockdown was effective. Infection numbers decreased as well in other municipalities without mandates. Control of infection pockets possibly together with voluntary social behaviour was apparently effective before the mandate which explains why the infection decline occurred before and in both the mandated and non-mandated areas. The findings of this study suggest that efficient infection surveillance and voluntary compliance make full lockdowns unnecessary at least in some circumstances.