Related: The WHO's six step guide to easing coronavirus lockdowns
More than three months on from the emergence in Wuhan of Covid-19, the lockdown gripping the Chinese city was finally lifted last week.
After a 76-day ban on travel, authorities allowed train, road and air links to start up after China’s infection rate plummeted to the extent that most new cases now involve people entering the country.
Some major Chinese population centres, such as Shanghai, plan to reopen schools this month, while restaurants are reopening in Beijing, albeit with tables kept apart.
While the UAE's stay-home orders and restrictions on travel continue, with the exception of allowing some shops to open for Ramadan, governments elsewhere are following China's lead in allowing some businesses to open amid concerns over the economic effects of shutdowns.
Austria is allowing garden centres to trade, some regions of Italy are permitting shops to open, while in Spain, where the rate of new infections has fallen, construction is starting up and factories are reopening.
Trying to predict what effects such loosening of restrictions may have is made more difficult by the fact that the coronavirus pandemic involves a new pathogen.
However, earlier outbreaks of another viral infection, influenza, offer pointers, even if infection patterns may not be the same.
Several years after the 2009 swine flu pandemic, where about one billion people are thought to have been infected and about 300,000 died, researchers concluded that closing schools in June that year curtailed a major outbreak, only for their reopening three months later to trigger new infections.
In a world where a small minority is immune to the novel coronavirus, the World Health Organisation has warned that infection rates could spike if lockdowns are lifted too early.
A number of academics, including Professor John Oxford, emeritus professor of virology at Queen Mary University of London and co-author of the textbook Human Virology, favour such a cautionary approach.
Saying that “all of us need patience”, he indicated that high levels of testing, quarantine and isolation, and continued lockdowns, were required.
The 1918 to 1920 Spanish flu pandemic is thought to have cost more than 50 million lives and was described by a Yale University academic writing in 1923 as, apart from the First World War, “perhaps the most terrible calamity that has afflicted the world since the Black Death of the fourteenth century”.
As outlined by the United States Centres for Disease Control and Prevention, measures to prevent infections included the use of disinfectants, better personal hygiene, isolation and quarantine, and limits on public gatherings.
A 2007 study by UK and Netherlands researchers published in the Proceedings of the National Academy of Sciences of the USA found that no US cities found the "optimal point" at which interventions produced a peak of minimal size during the 1918 outbreak. Nonetheless, the conclusions may be useful for today's policymakers.
“The cities that got closest to the theoretical maximum possible reduction in mortality were those that implemented both early and effective interventions throughout the first peak and then were able to reintroduce these when transmission again increased,” the authors wrote.
In 2013 researchers set out, using complex statistical methods, to tease apart the factors that may have affected 1918-20 pandemic’s complex pattern of infections, which saw some areas hit by as many as three outbreaks.
School openings and closures had an influence, as did the weather, because the infection rate fell as temperatures increased. Most important, though, was human behaviour, because people appear to have reduced contact with others in response to the outbreak.
Viral evolution may also affect a pandemic, creating a risk of later outbreaks if the pathogen becomes easier to transmit or more difficult for the immune system to fight off, mirroring the situation when a population lacks widespread “herd” immunity.
“We have to be very, very careful,” Prof John Oxford said, adding that China’s example “definitely” showed the importance of strict containment measures.
“You cannot be more strict than they were. They’ve knocked the virus on the head.
“At this stage of this new virus, it’s better to overreact in favour of stopping the virus rather than the other way around.”
Ultimately, though, with a new virus, the outcome remains uncertain. The world is, said Prof Oxford, “walking into unknown territory”.