Zero-COVID
Zero-COVID, also known as COVID-Zero and "Find, Test, Trace, Isolate, and Support", was a public health policy implemented by some countries, especially China, during the COVID-19 pandemic. In contrast to the "living with COVID-19" strategy, the zero-COVID strategy was purportedly one "of control and maximum suppression". Public health measures used to implement the strategy included as contact tracing, mass testing, border quarantine, lockdowns, and mitigation software in order to stop community transmission of COVID-19 as soon as it was detected. The goal of the strategy was to get the area back to zero new infections and resume normal economic and social activities.
A zero-COVID strategy consisted of two phases: an initial suppression phase in which the virus is eliminated locally using aggressive public health measures, and a sustained containment phase, in which normal economic and social activities resume and public health measures are used to contain new outbreaks before they spread widely. This strategy was utilized to varying degrees by Australia, Bhutan, Atlantic and Northern Canada, mainland China, Hong Kong, Macau, Malaysia, Montserrat, New Zealand, North Korea, Northern Ireland, Singapore, Scotland, South Korea, Taiwan, Thailand, Timor-Leste, Tonga, and Vietnam. By late 2021, due to challenges with the increased transmissibility of the Delta and Omicron variants, and also the arrival of COVID-19 vaccines, many countries had phased out zero-COVID, with mainland China being the last major country to do so in December 2022.
Experts have differentiated between zero-COVID, which was an elimination strategy, and mitigation strategies that attempted to lessen the effects of the virus on society, but which still tolerated some level of transmission within the community. These initial strategies could be pursued sequentially or simultaneously during the acquired immunity phase through natural and vaccine-induced immunity.
Advocates of zero-COVID pointed to the far lower death rates and higher economic growth in countries that pursued elimination during the first year of the pandemic compared with countries that pursued mitigation, and argued that swift, strict measures to eliminate the virus allowed a faster return to normal life. Opponents of zero-COVID argued that, similar to the challenges faced with the flu or the common cold, achieving the complete elimination of a respiratory virus like SARS-CoV-2 may not have been a realistic goal. To achieve zero-COVID in an area with high infection rates, one review estimated that it would take three months of strict lockdown.
Elimination vs. mitigation
Epidemiologists have differentiated between two broad strategies for responding to the COVID-19 pandemic: mitigation and elimination. Mitigation strategies aimed to reduce the growth of an epidemic and to prevent the healthcare system from becoming overburdened, yet still accepted a level of ongoing viral transmission within the community. By contrast, elimination strategies aimed to completely stop the spread of the virus within the community, which was seen as the optimal way to allow the resumption of normal social and economic activity. In comparison with mitigation strategies, elimination involved stricter short-term measures to completely eliminate the virus, followed by milder long-term measures to prevent a return of the virus.After elimination of COVID-19 from a region, zero-COVID strategies required stricter border controls in order to prevent reintroduction of the virus, more rapid identification of new outbreaks, and better contact tracing to end new outbreaks. Advocates of zero-COVID argued that the costs of these measures were lower than the economic and social costs of long-term social distancing measures and increased mortality incurred by mitigation strategies.
The long-term "exit path" for both elimination and mitigation strategies depended on the development of effective vaccines and treatments for COVID-19.
Containment measures
The zero-COVID approach aimed to prevent viral transmission using a number of different measures, including vaccination and non-pharmaceutical interventions such as contact tracing and quarantine. Successful containment or suppression reduced the basic reproduction number of the virus below the critical threshold. Different combinations of measures were used during the initial containment phase, when the virus was first eliminated from a region; and the sustained containment phase, when the goal was to prevent reestablishment of viral transmission within the community.Lockdowns
Lockdowns encompassed measures such as closures of non-essential businesses, stay-at-home orders, and movement restrictions. During lockdowns, governments were typically required to supply basic necessities to households. Lockdown measures were commonly used to achieve initial containment of the virus. In China, lockdowns of specific high-risk communities were also sometimes used to suppress new outbreaks.Quarantine for travelers
In order to prevent reintroduction of the virus into zero-COVID regions after initial containment had been achieved, quarantine for incoming travelers was commonly used. As each infected traveler could seed a new outbreak, the goal of travel quarantine was to intercept the largest possible percentage of infected travelers.International flights to China were heavily restricted, and incoming travelers were required to undergo PCR testing and quarantine in designated hotels and facilities. In order to facilitate quarantine for travelers, China constructed specialized facilities at its busiest ports of entry, including Guangzhou and Xiamen. New Zealand and Australia also established managed isolation and quarantine facilities for incoming travelers.
Through November 2020, border quarantine measures prevented nearly 4,000 infected international travelers from entering the wider community within China. Each month, hundreds of travelers who tested negative before flying to China subsequently tested positive while undergoing quarantine after arrival.
Contact tracing, quarantine, and isolation
Contact tracing involved identifying people who have been exposed to an infected person. Public health workers then isolated the known infected person and attempted to locate all of those exposed persons, and quarantine them until they either were unlikely to be infectious or received several negative tests. Various studies argued that early detection and isolation of infected people was the single most effective measure for preventing transmission of SARS-CoV-2. "Quarantine" referred to the separation of exposed persons who could have possibly been infected from the rest of society, while "isolation" referred to the separation of persons who were known to be infected.In China, when an infected person was identified, all close contacts were required to undergo a 14-day quarantine alongside multiple rounds of PCR testing. In order to minimize the risk that these close contacts posed for outbreak containment, China implemented quarantine in centralized facilities for those deemed to be at the highest-risk of infection. Secondary close contacts are sometimes required to quarantine at home.
The widespread use of smartphones enabled more rapid "digital" contact tracing. In China, "health code" applications were used to facilitate the identification of close contacts, via analysis of Bluetooth logs which show proximity between devices. Taiwan also made use of digital contact tracing, notably to locate close contacts of passengers who disembarked from the Diamond Princess cruise ship, the site of an early outbreak in February 2020.
Routine testing of key populations
In China, routine PCR testing was carried out on all patients who present with fever or respiratory symptoms. In addition, various categories of workers, such as medical staff and workers who handle imported goods, were regularly tested.In China, routine testing of key populations identified index patients in a number of outbreaks, including outbreaks in Beijing, Shanghai, Dalian, Qingdao, and Manchuria. In some cases, index patients had been discovered while asymptomatic, limiting the amount of onward transmission into the community.
Community-wide screening
An additional tool for identifying cases outside of known transmission chains was community-wide screening, in which populations of specific neighborhoods or cities were PCR tested. In China, community-wide PCR testing was carried out during outbreaks in order to identify infected people, including those without symptoms or known contact with infected people. Community-wide screening was intended to rapidly isolate infected people from the general population, and to allow a quicker return to normal economic activity. China first carried out community-wide screening from 14 May to 1 June 2020 in Wuhan, and used this technique in subsequent outbreaks. In outbreaks in June 2020 in Beijing and July 2020 in Dalian, community screening identified 26% and 22% of infections, respectively. In order to test large populations quickly, China commonly used pooled testing, combining five to ten samples before testing, and retesting all individuals in each batch that tested positive.Zero-COVID implementation by region
Australia
The first confirmed case in Australia was identified on 25 January 2020, in Victoria, when a man who had returned from Wuhan, Hubei Province, China, tested positive for the virus. A human biosecurity emergency was declared on 18 March 2020. Australian borders were closed to all non-residents on 20 March, and returning residents were required to spend two weeks in supervised quarantine hotels from 27 March. Many individual states and territories also closed their borders to varying degrees, with some remaining closed until late 2020, and continuing to periodically close during localised outbreaks.Social distancing rules were introduced on 21 March, and state governments started to close "non-essential" services. "Non-essential services" included social gathering venues such as pubs and clubs but unlike many other countries did not include most business operations such as construction, manufacturing and many retail categories.
During the second wave of May and June 2020, Victoria underwent a second strict lockdown with the use of helicopters and the Army to help the police enforce the Zero-COVID lockdown, which would become a norm of deployment, such as during the COVID-19 Delta variant outbreak in Sydney a year later. The wave ended with zero new cases being recorded on 26 October 2020. Distinctive aspects of that response included [|early interventions] to reduce reflected transmission from countries other than China during late January and February 2020; early recruitment of a large contact tracing workforce; comparatively high public trust in government responses to the pandemic, at least compared to the United States; and later on, the use of short, intense lockdowns to facilitate exhaustive contact tracing of new outbreaks. Australia's international borders also remained largely closed, with limited numbers of strictly controlled arrivals, for the duration of the pandemic. Australia sought to develop a Bluetooth-based contact tracing app that does not use the privacy-preserving Exposure Notification framework supported natively by Android and Apple smartphones, and while these efforts were not particularly effective, QR code–based contact tracing apps became ubiquitous in Australia's businesses.
In July 2021, the Australian National Cabinet unveiled plans to live with COVID and end lockdowns and restrictions contingent on high vaccine uptake. By August 2021, amid outbreaks in New South Wales, Victoria, and the ACT, Prime Minister Scott Morrison conceded a return to Zero-COVID was highly unlikely. Over the following months, each Australian jurisdiction began a living with COVID strategy either through ending lockdowns or voluntarily allowing the virus to enter by opening borders.