A new study based on China’s coronavirus trajectory has warned that countries wanting to lift lockdown restrictions and let life return to normal should maintain movement control measures until a vaccine against the virus becomes available.

Researchers in Hong Kong said the potential for a second wave of Covid-19 infections in China could increase “exponentially” if measures are relaxed too quickly and governments become complacent.

The study, published in The Lancet medical journal, used a model based on Covid-19 reproduction data from 10 Chinese provinces with the highest number of confirmed cases, as well as the confirmed case-fatality risk in all 31 provinces to determine the potential effects of relaxing lockdown measures after the first wave of infection.

Aggressive restrictions on daily life in China has been effective in reducing the number of coronavirus infections, with the average number of cases generated by a single infected individual falling to below one after lockdown measures were introduced.

But the potential for a second wave to arrive as the Chinese government begins to lift lockdown measures remains high.

Professor Joseph T Wu of the University of Hong Kong, who co-led the research, said: “While these control measures appear to have reduced the number of infections to very low levels, without herd immunity against Covid-19, cases could easily resurge as businesses, factory operations, and schools gradually resume and increase social mixing, particularly given the increasing risk of imported cases from overseas as Covid-19 continues to spread globally.

“Although control policies such as physical distancing and behavioural change are likely to be maintained for some time, proactively striking a balance between resuming economic activities and keeping the reproductive number below one is likely to be the best strategy until effective vaccines become widely available.”

The researchers said their findings are critical for countries in the early stages of a similar lockdown. The UK is entering its fourth week of lockdown, with all but key workers advised to stay and work from home wherever possible and most shops shut down.

Restrictions in several Chinese provinces have been gradually relaxed since 17 February, including in Hubei, the worst-hit region in the country. China entered its lockdown on 23 January after the outbreak began spreading rapidly from Wuhan.

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Co-lead author Dr Kathy Leung, also from the University of Hong Kong, said: “We are acutely aware that as economic activity increases across China in the coming weeks, local or imported infection could lead to a resurgence of transmission.”

Health care capacities should also be prioritised by governments when implementing interventions, said members of the Wuhan Municipal Health Commission in response to the study.

“While the epidemic is growing exponentially, the health care system will face severe burdens,” wrote Shunqing Xu and Yuanyuan Li.

“Governments should act and prepare immediately to ensure that the health care system has adequate labour, resources and facilities to minimise the mortality risk of Covid-19.”

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Researchers acknowledged limitations in their study, including that estimated reproductive numbers were based on the reported number of positive coronavirus cases, and that time and dates of symptom onset were not available for some provinces.

The study also did a limited number of simulations for relaxing lockdown measures and did not specify which interventions or public responses might correspond to each of these scenarios.