COVID-19 control in China during mass population movements at New Year.

The outbreak of novel coronavirus disease 2019 (COVID-19) continues to spread rapidly in China. The Chinese Lunar New Year holiday, the start of which coincided with the emergence of COVID-19, is the most celebratory time of the year in China, during which a massive human migration takes place as individuals travel back to their hometowns. People in China are estimated to make close to 3 billion trips over the 40-day travel period, or Chunyun, of the Lunar New Year holiday. About 5 million people left Wuhan, the capital city of Hubei province and epicentre of the COVID-19 epidemic, before the start of the travel ban on Jan 23, 2020. About a third of those individuals travelled to locations outside of Hubei province. Limiting the social contacts of these individuals was crucial for COVID-19 control, because patients with no or mild symptoms can spread the virus.

Government policies enacted during the Chinese Lunar New Year holiday are likely to have helped reduce the spread of the virus by decreasing contact and increasing physical distance between those who have COVID-19 and those who do not. As part of these social distancing policies, the Chinese Government encouraged people to stay at home; discouraged mass gatherings; cancelled or postponed large public events; and closed schools, universities, government offices, libraries, museums, and factories.6, 7, 8, 9, 10 Only limited segments of urban public transport systems remained operational and all cross-province bus routes were taken out of service. As a result of these policies and public information and education campaigns, Chinese citizens started to take measures to protect themselves against COVID-19, such as staying at home as far as possible, limiting social contacts, and wearing protective masks when they needed to move in public.

Social distancing has been effective in past disease epidemics, curbing human-to-human transmission and reducing morbidity and mortality.11, 12, 13, 14, 15, 16, 17 A single social distancing policy can cut epidemic spread, but usually multiple such policies—including more restrictive measures such as isolation and quarantine—are implemented in combination to boost effectiveness. For example, during the 1918–19 influenza pandemic, the New York City Department of Health enforced several social distancing policies at the same time, including staggered business hours, compulsory isolation, and quarantine, which likely led to New York City suffering the lowest death rate from influenza on the eastern seaboard of the USA.

During the current outbreak of COVID-19, government officials and researchers were concerned that the mass movement of people at the end of the Lunar New Year holiday on Jan 31, 2020, would exacerbate the spread of COVID-19 across China. Moreover, individuals typically return from their Lunar New Year holiday after only 1 week, which is shorter than the longest suspected incubation period of the disease. Many of the 5 million people who left Wuhan before the travel ban was put into place could still have been latently infected when their holiday ended. This situation, together with the resumed travel activities, would make it difficult to contain the outbreak.

Facing these concerns, the Chinese Government extended the Lunar New Year holiday. The holiday end date was changed to March 10 for Hubei province and Feb 9 for many other provinces, so that the duration of the holiday would be sufficiently long to fully cover the suspected incubation period of COVID-19.20, 21, 22 In addition, people diagnosed with COVID-19 were isolated in hospitals. In Wuhan, where the largest number of infected people live, those with mild and asymptomatic infection were also quarantined in so-called shelter or “Fang Cang” hospitals, which are public spaces such as stadiums and conference centres that have been repurposed for medical care. Finally, the Chinese Government encouraged and supported grassroots activities for routine screening, contact tracing, and early detection and medical care of COVID-19 patients, and it promoted hand washing, surface disinfection, and the use of protective masks through social marketing and media. As a result of the extended holiday and the additional measures, many people with asymptomatic infection from Hubei province who had travelled to other provinces remained in their homes until they developed symptoms, at which point they received treatment. It is this home-based quarantine of people who had been to the epicentre of the epidemic and travelled to other locations in China that is likely to have been especially helpful in curbing the spread of the virus to the wider community.

There are several lessons that can be drawn from China's extension of the Lunar New Year holiday. First, countries facing potential spread of COVID-19, or a similar outbreak in the future, should consider outbreak-control “holidays” or closure periods—ie, periods of recommended or mandatory closure of non-essential workplaces and public institutions—as a first-line social distancing measure to slow the rate of transmission. Second, governments should tailor the design of such outbreak-control closure periods to the specific epidemic characteristics of the novel disease, such as the incubation period and transmission routes. Third, a central goal of an outbreak-control closure period is to prevent people with asymptomatic infections from spreading the disease. As such, governments should use the closure period for information and education campaigns, community screening, active contact tracing, and isolation and quarantine to maximise impact. Such a combination approach is also supported by studies of responses to previous outbreaks, which showed that reductions in the cumulative attack rate were more pronounced when social distancing policies were combined with other epidemic control measures to block transmission.

As for COVID-19 in China, this combination of an outbreak-control closure period for social distancing and a range of accompanying epidemic control measures seems to have prevented new infections, especially in provinces other than Hubei, where new infections have been declining for more than 2 weeks. As fearsome and consequential as the COVID-19 outbreak has been, China's vigorous, multifaceted response is likely to have prevented a far worse situation. Future empirical research will establish the full impact of the social distancing and epidemic control policies during the extended Chinese Lunar New Year holiday. As travel and work slowly resume in China, the country should consider at least partial continuation of these policies to ensure that the COVID-19 outbreak is sustainably controlled.