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COVID-19: examining the effectiveness of non-pharmaceutical interventions - Published Aug 2023 (PDF)
© The Royal Society
The text of this work is licensed under the terms of the Creative Commons Attribution License which permits unrestricted use, provided the original author and source are credited.
The license is available at:
creativecommons.org/licenses/by/4.0
Executive summary
Introduction
The purpose of this report from the Royal Society is to assess what has been learnt about the effectiveness of the application of non-pharmaceutical interventions (NPIs) during the COVID-19 pandemic of 2020 – 2023 by assembling and examining evidence from researchers around the world. These NPIs were a set of measures (described in Box 1) aimed at reducing the person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that caused the pandemic. Six groups of researchers were commissioned to assemble evidence reviews for this report, examining the effectiveness of a range of NPIs that were applied with the aim of reducing the transmission of SARS-CoV-2. Researchers were tasked with documenting what has been learnt, identifying gaps in knowledge and considering how these might be filled in the future. This report summarises these evidence reviews and interprets them alongside national case studies. It pays particular attention to the context and the constraints on the types of research that could be and were performed during the pandemic. The report is non-judgemental on the timing and manner in which NPIs were applied in different regions and countries around the world. It focuses on understanding the impact of NPIs on SARS-CoV-2 transmission and makes no assessment of the economic or other societal impacts of the different NPIs. Assessing these other impacts are important tasks for the many different COVID-19 inquiries that are underway around the world.
From the start of the pandemic, rapidly growing scientific information was deployed continuously to help to control its spread. The genome of the causative virus, SARS-CoV-2, was sequenced from some of the very earliest samples available from infected humans in China. This sequence information enabled the development of precise molecular diagnostic tests that could be used for diagnosis and mass testing of populations, the development of vaccines and continuous monitoring of the evolution of the virus. The development of tests led to the widespread implementation of ‘test, trace and isolate’ interventions early in the pandemic. COVID-19 was the first pandemic in which it was feasible to conduct prophylactic and therapeutic drug trials and to create novel vaccines during the course of the pandemic, saving lives and modifying the outcomes. However, despite extraordinary scientific capabilities, for most of the first year of the pandemic the only measures available to slow the transmission of the novel virus were NPIs. For those that were infected and seriously ill, there were no specific treatments or preventative measures in the form of drugs or vaccines. The supportive measures of modern medicine, such as oxygen supplementation, pulmonary ventilation and other forms of advanced life support, saved many lives, but did nothing to slow transmission.
What are NPIs?
The principles behind NPIs are firmly grounded in prior knowledge about the epidemiology and biology of infectious diseases. In essence, the transmission of an infection from one human to another can be prevented if the transmission pathway can be blocked effectively. For an airborne virus such as SARSCoV-2, effective measures reduce exposure to virus that has been exhaled by infected people (by breathing, talking, coughing or sneezing). Measures that can assist, in theory, include the wearing of face masks, enhanced ventilation and social distancing. Where infectious virus survives on surfaces (furniture, clothes or hands), cleaning regimes including enhanced handwashing can help. Personal protection equipment (PPE), common in healthcare environments (including gloves, visors, gowns and masks) potentially offers protection against exposure.
Early clinical studies of COVID-19 strongly suggested that the primary routes for acquiring infection were likely to be by direct inhalation or exposure of the mucosal surfaces of the nose and mouth to virus suspended in airborne droplets or, as was realised some months into the pandemic, in aerosols. Early evidence of fomites (contaminated surfaces), extensively contaminated with SARS-CoV-2 viral nucleic acid shed from infected people, pointed to the possibility that hand-to-face contact might also transmit the infection. This view was informed by prior knowledge of the transmission mechanisms of other respiratory viruses, such as influenza, respiratory syncytial virus (RSV) and the coronavirus (now named SARS-CoV-1) that caused the SARS outbreak in several countries around the world in 2003.
Use of NPIs for infectious disease control
Considering the incomplete knowledge about this new viral infection and prior knowledge, many governments around the world implemented measures similar to those used just over a century earlier during the 1918 influenza pandemic. Some countries in Asia implemented measures based on their more recent experience of outbreaks of SARS and Middle East Respiratory Syndrome (MERS). NPIs included the wearing of masks and enhanced personal hygiene measures, including enhanced surface cleaning and handwashing. Social distancing was introduced and enforced to variable extents. Social distancing measures included closures of schools and workplaces, as well as entertainment, leisure and sporting venues. These closures were often augmented by stayat-home orders for all but essential workers.
Border controls and closures were put in place in many countries with the aim of reducing the movement of cases across national borders. The precise measures, and the ways they were implemented, varied between countries according to their social and political-economic contexts and prior experiences. In most of the world, NPIs remained the dominant mechanism for control of the pandemic until well into its second year. The UK was the first country to approve the use of vaccines against SARS-CoV-2, approving three vaccines during December 2020 and January 2021. By July 2021, approximately half of the UK’s population had received two doses of vaccine. However, it took until January 2022 for half of the global population to have had two doses – and a year later in January 2023 the global figure had risen to approximately 63%.
The challenge for governments around the world facing a pandemic is how to minimise the harms to their populations. The harms of a pandemic are the morbidity and mortality from the viral infection, coupled with the social disruption and harms that follow from the direct and indirect consequences of that morbidity and mortality. The latter can be exceptionally severe if the extent of illness and social response to the illness disrupts the healthcare systems, infrastructure, goods and services on which the health, wellbeing, resilience and security of the population depend.
What are non-pharmaceutical interventions (NPIs)?
NPIs include any measure that is implemented during an infectious disease outbreak to attempt to reduce transmission that is not a vaccine or drug. NPIs can be behavioural, social, physical, or
regulatory in nature. Their uptake and use can be encouraged through a variety of approaches, escalating from advice and guidance through to regulation. NPIs are therefore the first line of defence in the effort to contain outbreaks and to limit the impacts on affected populations before biological interventions become available. They have also been used alongside vaccines and drugs, especially where these interventions fail to prevent transmission. The precise ways in which NPIs were implemented during the COVID-19 pandemic varied between different countries and contexts.
The programme of work described in this report covered six broad categories of NPIs and the evidence available concerning= their effectiveness at reducing transmission of SARS-CoV-2. The six categories are as follows:
Masks and face coverings
Masks act as barriers to virus particles in air being inhaled and/or exhaled through the nose or mouth. Virus-carrying droplets (larger, heavier particles) or aerosols (smaller, lighter articles) captured on the inside or outside of the mask can no longer spread via the air. The materials and features of masks affect the size of the particles that are filtered out, and their resulting effectiveness. How well the mask fits the face of the wearer is also key. N95 masks (also known as respirators), when worn correctly, are highly effective barriers.
Social distancing and ‘lockdowns’
Respiratory diseases are transmitted by infectious material carried by exhalations (eg. breathing, talking, coughing or sneezing) from one individual to another. Increasing physical distance between individuals can reduce the amount of infectious material being carried to others in droplets and aerosols, although aerosols typically transmit over longer distances than droplets. A commonly recommended minimum distance of separation between individuals during the COVID-19 pandemic was two metres. Interventions on populations and communities included closures of schools, workplaces, places of worship and entertainment venues, as well as ‘stay-at-home’ orders (‘lockdowns’) that prevented most people from coming into
contact with anyone outside their own homes.
Test, trace and isolate
SARS-CoV-2 is transmitted when infected individuals are in close proximity to others. A strategy employed to break the chain of transmission is to identify infectious people (‘test’), determine with whom they have come into physical contact (‘trace’) and encourage or enforce both infected individuals and their contacts to stay at home and avoid physical contact with others until the risk of being infectious has subsided (‘isolate’).
Travel restrictions and controls across international borders
During a pandemic, where an infectious disease is spreading across international borders, restricting the ability of people to move between countries can be used to try to prevent the global movement of the pathogen. Border controls applied during
the pandemic varied in stringency and took
the form of complete or partial bans targeted
at international travellers from particular
regions perceived as being at higher risk.
Often border controls were accompanied by
requirements for international travellers to test
and/or quarantine at the border of departure
and/or arrival to enable some travel.
Environmental controls
Particles carrying infectious material vary in size from droplets that settle on surfaces close to the point of exhalation through to very fine aerosols which can linger in the air and travel further. Certain elements of building design and management can be implemented with the intention of restricting the spread of respiratory pathogens. These include enhancing ventilation systems to
replace air carrying infectious aerosols with outside air, and filtering or treating air inside buildings to reduce infectious virus. Screens made of a variety of materials and reduced occupancy limits for rooms or buildings can also be used. Environmental controls also include cleaning of surfaces to remove droplets carrying infectious material and enhanced handwashing.
Communications
Effective communication about any of thephysical, social or behavioural interventions is essential if people are to understand and be convinced of the reason for their use, as well as being willing to adopt and maintain the practices, and to do so correctly, so as to maximise effectiveness.
© The Royal Society
The text of this work is licensed under the terms of the Creative Commons Attribution License which permits unrestricted use, provided the original author and source are credited.
The license is available at:
creativecommons.org/licenses/by/4.0
Executive summary
Introduction
The purpose of this report from the Royal Society is to assess what has been learnt about the effectiveness of the application of non-pharmaceutical interventions (NPIs) during the COVID-19 pandemic of 2020 – 2023 by assembling and examining evidence from researchers around the world. These NPIs were a set of measures (described in Box 1) aimed at reducing the person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that caused the pandemic. Six groups of researchers were commissioned to assemble evidence reviews for this report, examining the effectiveness of a range of NPIs that were applied with the aim of reducing the transmission of SARS-CoV-2. Researchers were tasked with documenting what has been learnt, identifying gaps in knowledge and considering how these might be filled in the future. This report summarises these evidence reviews and interprets them alongside national case studies. It pays particular attention to the context and the constraints on the types of research that could be and were performed during the pandemic. The report is non-judgemental on the timing and manner in which NPIs were applied in different regions and countries around the world. It focuses on understanding the impact of NPIs on SARS-CoV-2 transmission and makes no assessment of the economic or other societal impacts of the different NPIs. Assessing these other impacts are important tasks for the many different COVID-19 inquiries that are underway around the world.
From the start of the pandemic, rapidly growing scientific information was deployed continuously to help to control its spread. The genome of the causative virus, SARS-CoV-2, was sequenced from some of the very earliest samples available from infected humans in China. This sequence information enabled the development of precise molecular diagnostic tests that could be used for diagnosis and mass testing of populations, the development of vaccines and continuous monitoring of the evolution of the virus. The development of tests led to the widespread implementation of ‘test, trace and isolate’ interventions early in the pandemic. COVID-19 was the first pandemic in which it was feasible to conduct prophylactic and therapeutic drug trials and to create novel vaccines during the course of the pandemic, saving lives and modifying the outcomes. However, despite extraordinary scientific capabilities, for most of the first year of the pandemic the only measures available to slow the transmission of the novel virus were NPIs. For those that were infected and seriously ill, there were no specific treatments or preventative measures in the form of drugs or vaccines. The supportive measures of modern medicine, such as oxygen supplementation, pulmonary ventilation and other forms of advanced life support, saved many lives, but did nothing to slow transmission.
What are NPIs?
The principles behind NPIs are firmly grounded in prior knowledge about the epidemiology and biology of infectious diseases. In essence, the transmission of an infection from one human to another can be prevented if the transmission pathway can be blocked effectively. For an airborne virus such as SARSCoV-2, effective measures reduce exposure to virus that has been exhaled by infected people (by breathing, talking, coughing or sneezing). Measures that can assist, in theory, include the wearing of face masks, enhanced ventilation and social distancing. Where infectious virus survives on surfaces (furniture, clothes or hands), cleaning regimes including enhanced handwashing can help. Personal protection equipment (PPE), common in healthcare environments (including gloves, visors, gowns and masks) potentially offers protection against exposure.
Early clinical studies of COVID-19 strongly suggested that the primary routes for acquiring infection were likely to be by direct inhalation or exposure of the mucosal surfaces of the nose and mouth to virus suspended in airborne droplets or, as was realised some months into the pandemic, in aerosols. Early evidence of fomites (contaminated surfaces), extensively contaminated with SARS-CoV-2 viral nucleic acid shed from infected people, pointed to the possibility that hand-to-face contact might also transmit the infection. This view was informed by prior knowledge of the transmission mechanisms of other respiratory viruses, such as influenza, respiratory syncytial virus (RSV) and the coronavirus (now named SARS-CoV-1) that caused the SARS outbreak in several countries around the world in 2003.
Use of NPIs for infectious disease control
Considering the incomplete knowledge about this new viral infection and prior knowledge, many governments around the world implemented measures similar to those used just over a century earlier during the 1918 influenza pandemic. Some countries in Asia implemented measures based on their more recent experience of outbreaks of SARS and Middle East Respiratory Syndrome (MERS). NPIs included the wearing of masks and enhanced personal hygiene measures, including enhanced surface cleaning and handwashing. Social distancing was introduced and enforced to variable extents. Social distancing measures included closures of schools and workplaces, as well as entertainment, leisure and sporting venues. These closures were often augmented by stayat-home orders for all but essential workers.
Border controls and closures were put in place in many countries with the aim of reducing the movement of cases across national borders. The precise measures, and the ways they were implemented, varied between countries according to their social and political-economic contexts and prior experiences. In most of the world, NPIs remained the dominant mechanism for control of the pandemic until well into its second year. The UK was the first country to approve the use of vaccines against SARS-CoV-2, approving three vaccines during December 2020 and January 2021. By July 2021, approximately half of the UK’s population had received two doses of vaccine. However, it took until January 2022 for half of the global population to have had two doses – and a year later in January 2023 the global figure had risen to approximately 63%.
The challenge for governments around the world facing a pandemic is how to minimise the harms to their populations. The harms of a pandemic are the morbidity and mortality from the viral infection, coupled with the social disruption and harms that follow from the direct and indirect consequences of that morbidity and mortality. The latter can be exceptionally severe if the extent of illness and social response to the illness disrupts the healthcare systems, infrastructure, goods and services on which the health, wellbeing, resilience and security of the population depend.
What are non-pharmaceutical interventions (NPIs)?
NPIs include any measure that is implemented during an infectious disease outbreak to attempt to reduce transmission that is not a vaccine or drug. NPIs can be behavioural, social, physical, or
regulatory in nature. Their uptake and use can be encouraged through a variety of approaches, escalating from advice and guidance through to regulation. NPIs are therefore the first line of defence in the effort to contain outbreaks and to limit the impacts on affected populations before biological interventions become available. They have also been used alongside vaccines and drugs, especially where these interventions fail to prevent transmission. The precise ways in which NPIs were implemented during the COVID-19 pandemic varied between different countries and contexts.
The programme of work described in this report covered six broad categories of NPIs and the evidence available concerning= their effectiveness at reducing transmission of SARS-CoV-2. The six categories are as follows:
Masks and face coverings
Masks act as barriers to virus particles in air being inhaled and/or exhaled through the nose or mouth. Virus-carrying droplets (larger, heavier particles) or aerosols (smaller, lighter articles) captured on the inside or outside of the mask can no longer spread via the air. The materials and features of masks affect the size of the particles that are filtered out, and their resulting effectiveness. How well the mask fits the face of the wearer is also key. N95 masks (also known as respirators), when worn correctly, are highly effective barriers.
Social distancing and ‘lockdowns’
Respiratory diseases are transmitted by infectious material carried by exhalations (eg. breathing, talking, coughing or sneezing) from one individual to another. Increasing physical distance between individuals can reduce the amount of infectious material being carried to others in droplets and aerosols, although aerosols typically transmit over longer distances than droplets. A commonly recommended minimum distance of separation between individuals during the COVID-19 pandemic was two metres. Interventions on populations and communities included closures of schools, workplaces, places of worship and entertainment venues, as well as ‘stay-at-home’ orders (‘lockdowns’) that prevented most people from coming into
contact with anyone outside their own homes.
Test, trace and isolate
SARS-CoV-2 is transmitted when infected individuals are in close proximity to others. A strategy employed to break the chain of transmission is to identify infectious people (‘test’), determine with whom they have come into physical contact (‘trace’) and encourage or enforce both infected individuals and their contacts to stay at home and avoid physical contact with others until the risk of being infectious has subsided (‘isolate’).
Travel restrictions and controls across international borders
During a pandemic, where an infectious disease is spreading across international borders, restricting the ability of people to move between countries can be used to try to prevent the global movement of the pathogen. Border controls applied during
the pandemic varied in stringency and took
the form of complete or partial bans targeted
at international travellers from particular
regions perceived as being at higher risk.
Often border controls were accompanied by
requirements for international travellers to test
and/or quarantine at the border of departure
and/or arrival to enable some travel.
Environmental controls
Particles carrying infectious material vary in size from droplets that settle on surfaces close to the point of exhalation through to very fine aerosols which can linger in the air and travel further. Certain elements of building design and management can be implemented with the intention of restricting the spread of respiratory pathogens. These include enhancing ventilation systems to
replace air carrying infectious aerosols with outside air, and filtering or treating air inside buildings to reduce infectious virus. Screens made of a variety of materials and reduced occupancy limits for rooms or buildings can also be used. Environmental controls also include cleaning of surfaces to remove droplets carrying infectious material and enhanced handwashing.
Communications
Effective communication about any of thephysical, social or behavioural interventions is essential if people are to understand and be convinced of the reason for their use, as well as being willing to adopt and maintain the practices, and to do so correctly, so as to maximise effectiveness.