At least 11 countries have reimposed restrictions amid fears of coronavirus second wave

The delicate balance between restarting economies and avoiding a second wave of coronavirus is being played out across the world.

While the chance of dying from the virus now appears to be very low, particularly for younger people, it has the potential to be indiscriminately lethal and operates in a way we still do not fully understand.

Yet lockdown is undoubtedly devastating for livelihoods, education and mental and physical health, and cannot continue for much longer without long-term implications that could last a generation.

Treading the line between release and restriction is proving tricky for many countries. At least 11 have now reimposed some, or all, lockdown restrictions to prevent a deadly second wave after virus cases began to rise when measures were relaxed.

Japan, China, South Korea, Lebanon, Germany, Iran, Saudi Arabia, El Salvador, Iraq, Sri Lanka and Pakistan have all been forced to bring back localised quarantines or widespread shutdowns.

Dr Hans Kluge, the director for the World Health Organisation (WHO) European region, has warned European countries to brace themselves for a deadly second wave of virus infections, saying now is the "time for preparation, not celebration".

Japan was the first country to experience a second wave after lifting lockdown restrictions in mid-March. By April 12, the country had declared a second state of emergency, ordering the closure of schools, stopping large gatherings and asking people to stay at home.

The Japanese prime minister, Shinzo Abe, lifted measures for Tokyo and four remaining areas last week after infections fell across the country, but warned that they could be reimposed if the virus started spreading again.

Nearly six and half million people worldwide have been infected, and recent figures from the Office for National Statistics (ONS) suggest that the number is probably much higher because so many people are asymptomatic.

The lack of symptoms mean many will never know they have the virus and so do not know they need to self-isolate and may be continuing its spread.

There is no way that the Government's test, track and trace scheme would ever pick up these people, and they make up the majority of cases.

In the past week, experts have raised concerns about easing lockdown measures in Britain before case numbers have fallen sufficiently.

The ONS estimates there are currently 8,000 infections a day, and with a death rate of around one per cent that equates to the country flatlining at around 80 deaths per day as the 'R' rate is currently close to one.

Britain initially planned to keep cases at a low level – or "squash the sombrero", as Boris Johnson termed it – to avoid a second peak. But after Imperial College London modelling suggested that 500,000 people could die as a result, the strategy changed to one of suppression.

Although it has kept cases at a low level it makes the country far more vulnerable to a second wave because so few people have herd immunity.

Other countries which managed to keep cases low have experienced a resurgence. South Korea, which initially kept a lid on the epidemic through intense track and trace measures, recently closed museums, parks and art galleries after a wave of new cases in Seoul.

Likewise China, which released strict lockdown measures on April 8 after 11 weeks, was forced to bring back restrictions in Wuhan and revert back to high alert from medium status in Shulan.

On May 8, local governments in Germany had to activate emergency measures in three districts that have seen flare-ups of the virus at local meatpacking centres in North Rhine-Westphalia and Schleswig-Holstein.

Iran's cases, which were declining until May 2, began to steadily climb again and had more than doubled within a fortnight after restrictions were lifted.

In mid-May, Lebanon brought restrictions back after experiencing a surge of infections almost exactly two weeks after it began easing measures. And last weekend, Iraq reimposed total lockdown as Covid-19 cases began rising again. Sri Lanka, El Salvador, Saudi Arabia and Pakistan have also reintroduced some measures.

Professor Mark Woolhouse, of the University of Edinburgh, who sits on the UK Government's Scientific Advisory Group for Emergencies (Sage) has warned that a second wave is a "clear and present danger".

"The lockdown was never intended to be permanent – it's clearly not possible," he said. "So ideally we would like to get 'R' down by using a vaccine, and we call that herd immunity. We don't have a vaccine and we're quite far from natural herd immunity, and it doesn't look like we can eliminate it.

"So the conclusion from that is that the second wave really is a clear and present danger. Even if we succeed in driving levels of infection very low, then we're looking at containment. Containment is what the UK was trying to do right at the beginning of this epidemic.

"Intensive surveillance, large-scale screening, effective contact tracing, isolation of cases, quarantining of those exposed, quarantine screening of international arrivals and some residual social distancing.

"That is a possible new normal – and if we don't like we're going to have to find other ways of living with Covid-19, because it's not going away any time soon."

In Sweden, scientists chose to impose few measures for fear of suppressing the virus so much that a deadly second wave became more likely.

This week, giving evidence to the science and technology committee, Professor Neil Ferguson said he had the "greatest respect for scientists there" who "came to a different policy conclusion but based really on quite similar science".

He added: "They make the argument that countries will find it very hard to really stop second waves... I don't agree with it, but scientifically they are not that far from scientists in any country in the world."