Welcome to this week’s roundup of developments from the coronavirus pandemic. As more countries eased out of lockdown, scientists shed light on how the virus attacks and raised questions over wastewater that drains from sinks and bathrooms.

Lockdowns work

Substantial lockdowns around the world have taken their toll on millions of lives and dented economies globally. So it was a relief to hear that the bluntest tool of all in the outbreak management toolbox worked. Lockdowns in Europe spared more than 3 million lives, including an estimated 470,000 in the UK, 690,000 in France, and 630,000 in Italy, according to researchers at Imperial College London.

Outbreak modellers found that lockdown slashed the average number of people that contagious individuals infected by 81%. In the UK, that amounted to lowering the all-important reproduction number of the virus, R, from 3.8 to 0.63, they reported in Nature. In 11 countries from France and Germany to Spain and Italy, lockdown pushed the R value below one, meaning the epidemics went into decline.

The modelling showed that by 4 May between 12 million and 15 million people in those countries had been infected by coronavirus but “attack rates” varied dramatically, from 0.46% of Norwegians infected to 8% of Belgians. In the UK an estimated 5.1% were infected. Prof Axel Gandy, a statistician on the team, said the model suggested “we are very far away from herd immunity”, where at least two-thirds of the population have acquired protective immunity to the disease. “We need to tread very carefully,” he added.

More work on lockdowns came from the University of California, Berkeley. Scientists there estimated that lockdowns in the US, France, China, South Korea and Iran had prevented about 530m infections. The research came as New Zealand’s prime minister, Jacinda Ardern, declared the country virus-free and scrapped all coronavirus restrictions, except strict border controls.

Enter the virus

Scientists worked out early on how the virus invades human cells and establishes infections. Spikes on the virus bind to so-called ACE-2 receptors that pepper the surfaces of many human cells, most importantly those in the respiratory tract. Once latched on, the virus gains entry and replicates over and over, until millions burst out to infect more cells.

But that might not be the only way in. Separate teams led by the Technical University of Munich and Bristol University found that the virus attaches to a second human cell receptor called NRP1. Like ACE-2, it peppers cells in the respiratory tract, but it is also abundant in olfactory tissues, those that are used to smell.

Both groups found that blocking the receptor prevented the virus from infecting human cells in the lab, adding weight to the idea that it is important. What is most intriguing about the receptor is that it may be a gateway to the brain, and in particular allow the virus to reach olfactory centres and potentially disrupt the sense of smell.

The two papers are tentative for now and have yet to be published in scientific journals. But if the results are sound, they might explain some of the disease’s stranger symptoms and help to steer future vaccine design.

Keep your distance

Politicians on either sides of the Atlantic became embroiled in debates over safe distancing. The US vice president, Mike Pence, posted – and then swiftly deleted – a photo of President Donald Trump’s re-election campaign staff displaying zero physical distancing. Meanwhile in the UK, the Tories piled pressure on Boris Johnson to reduce the 2m distancing guideline to 1m, amid concerns for the economy, in particular pubs, cafes and restaurants. Johnson made clear he wants to ease the rule, but uncertainty around whether the advice will be changed caused chaos for councils and retailers, who may have wasted millions of pounds on signs and other preparations for reopening the high streets.

Prof Susan Michie, who sits on the behavioural science subgroup of the government’s Sage committee of experts, said reducing the distance to 1m would undermine messages of how the virus is transmitted. “It seems to me that now is not the time to be lifting restrictions unless there’s a very good argument. The risks will be higher and more people will get ill,” she said.

This Science Weekly podcast looks at the psychology of physical distancing. As the world begins to unlock, many of us will be seeing friends and family again – albeit with guidelines on how close you can get to one another. But why is it more difficult to stay physically apart from friends and family than a stranger in a supermarket queue? Nicola Davis speaks to Prof John Drury about the psychology of physical distancing and why we like to be near those we feel emotionally close with

Watch the wastewater

With so many people in lockdown, scientists turned their attention away from the most common route of spreading the disease – inhalation of virus-laden droplets from an infected person – to the domestic risk of contaminated surfaces and wastewater. Previous research has shown that the virus can survive for anything from four hours on a copper surface to five days on glass, with cardboard, plastic and wood all lying somewhere between. What was less clear was how often domestic objects and surfaces are contaminated with the virus.

A team of virologists at the University of Bonn hunted for the virus in air samples, wastewater and on surfaces in 21 randomly-selected households. All were in quarantine after at least one member tested positive for the virus. None of the air samples tested positive for the virus, but among the water samples taken from sinks, showers and toilets, 15.5% did contain the virus. Strikingly, tests on 119 surfaces, including door knobs, handles, electronic gadgets, furnishings, food and drink items, clothes, plants and pets, yielded only four positives. These came from one TV remote control, two metal doorknobs and one wooden stove overlay. The scientists could not grow infectious virus from any of the samples they collected.

The researchers are not suggesting that people ease up on hand-washing or cleaning surfaces, particularly when sharing a home with an infected person. But the work, which has yet to be peer-reviewed, suggests that while wastewater deserves more attention, surfaces may not be a major source of infection.