Lockdowns imposed to curb the spread of Covid-19 have saved more than three million lives across Europe, according to a new study.
Scientists at Imperial College London who led the research warned that easing the lockdown too much may cause a second spike of coronavirus infections.
"The risk of a second wave happening if all interventions and all precautions are abandoned is very real," Imperial's Samir Bhatt, who led the research, told reporters after the paper was published on Monday.
Worried about the economic impact of their lockdowns, most European countries have started to ease restrictions as the number of new coronavirus cases fall.
The Imperial team estimated that by early May, between 12 and 15 million people in total in Austria, Belgium, Britain, Denmark, France, Germany, Italy, Norway, Spain, Sweden and Switzerland - around 4 per cent of their combined population - had been infected with the novel coronavirus. By then, roughly 130,000 people had died from Covid-19 in those countries.
By comparing the number of deaths counted with deaths predicted by their model if no lockdown measures had been introduced, they found some 3.1 million deaths were averted.
"Lockdown averted millions of deaths, those deaths would have been a tragedy," said Dr Seth Flaxman, from Imperial.
The study analysed the impact of lockdowns and social distancing in the 11 European countries and found they had "a substantial effect", helping to lower the infection's reproductive rate, or R value, below one by early May.
The R value measures the average number of people that one infected person will pass the disease on to. If the value is about one, the virus can spread exponentially.
"But any claims that this is all over, that we've reached the herd immunity threshold, can be firmly rejected," Mr Bhatt said. "We are only at the beginning of this pandemic."
Another study that was also released on Monday but in the United States, estimated that lockdowns in China, South Korea, Italy, Iran, France and the United States had prevented or delayed around 530 million Covid-19 cases.
Focusing on those six nations, the US team compared infection growth rates before and after the implementation of more than 1,700 local, regional and national policies designed to slow or halt the spread of Covid-19.
They found that without lockdowns in place, early infection rates of SARS-CoV-2 grew by 68 per cent a day in Iran and an average of 38 per cent a day across the other five countries.