The coronavirus required a different response, says Michael Baker, a professor in the Department of Public Health at the University of Otago, in Wellington, who advised the New Zealand government on the country’s Covid-19 response. Flu typically has an incubation period – the time between someone becoming infected and showing symptoms – of about one to two days. This makes it extremely difficult to trace the contacts of an infected person before they get sick themselves.

The coronavirus, on the other hand, appears to have an incubation period of about five to six days, but potentially several weeks. “It means that it’s a slower moving wave and there are more opportunities to use contact tracing and isolation and quarantine,” says Baker. “We know that’s the case because [the] Sars [coronavirus] was contained and eliminated with those traditional measures.”

In addition, while flu can “sweep through a population in a matter of weeks”, he says, the coronavirus can stick around for much longer and can have lasting health effects for those who survive it. This is one reason the idea of waiting to achieve herd immunity rather than taking action to limit the impact of the virus – a strategy the British and Swedish governments initially considered – was widely dismissed by the scientific community.

Britain has the highest number of recorded coronavirus cases in western Europe, probably in part due to the British government’s delayed response to the outbreak. One factor that unites the nations that have done a better job at limiting case numbers is a quick initial response.

“In countries like China, South Korea, Japan, the initial response was quite rapid, so the containment phase worked really well for them,” says Rajiv Chowdhury, an associate professor of global health at the Univer­sity of Cambridge, in Britain. By quickly identifying new cases and where they were coming from, these countries stood a much better chance of interrupting the ongoing transmission of the virus, he says.

Well-timed lockdowns

“When you just let things go, and don’t implement any control measures […] I think we’ve seen that the results can be devastating,” says Susy Hota, an infectious diseases specialist at the University Health Network, in Canada.

Lockdown rules have varied widely worldwide, but implementing restrictions early on worked well for many countries, including China and New Zealand.

New Zealand’s lockdown was particularly strict: schools, universities and almost all businesses were shut, and people could leave their homes only for essential reasons. Such measures succeeded in lowering the R number – the average number of people one person with the virus will go on to infect – from about two to around 0.5 within five weeks, says Baker.

Modelling has suggested that implementing lockdown just a week earlier in Britain could have avoided 20,000 deaths.

But lockdowns don’t necessarily work the same way in low- and middle-income countries, where it can be much harder for people living in low-quality housing in densely populated areas to stay home and lose out on income, says Chowdhury. Because such nations may only be able to sustain short-term lockdowns, the timing of these restrictions is crucial, he says.

Chowdhury points out that many countries in South Asia and Central and South America imposed lockdowns when European ones did. At that point, cases were soaring in Europe, while there were few in many low-income nations. In theory, it makes sense to introduce lockdown while cases are still low, says Chowdhury. But because of the difficulties in enforcing restrictions, case numbers continued to rise.

Cases are now climbing in many countries where governments have eased restrictions that have become economically unsustainable. “That’s a trend I see in many countries in Latin America, Southeast Asia and Africa,” says Chowdhury.

Sick with Covid-19, Brazil president puts faith in hydroxychloroquine

These and other regions are fast becoming the next coronavirus hot spots. Many people in Bangladesh, for example, found it hard to comply with lockdown restric­tions, with almost three-quarters of those in urban areas losing their main source of income.

In Brazil, mixed messaging from the government weakened the impact of lockdown. The virus is currently spreading significantly in both countries.

Alternative approaches may work better in some countries, says Chowdhury. The World Health Organisation has recommended that Pakistan, which has also experi­enced a spike in cases, impose a rolling two-week-on, two-week-off lockdown, for instance. More localised lockdowns could also be effective. This approach has already been adopted in a number of other countries, including in the British city of Leicester.

Travel restrictions

Lockdown alone isn’t enough, however. Since the beginning of the outbreak, the value of testing people, tracing their contacts and encouraging them to isolate themselves has become clear.

“It has proven to be important, not just for helping to interrupt transmission […] but also for us to better under­stand where transmission is occurring, so we can have targeted efforts to protect people in those environments,” says Nuzzo.

Part of New Zealand’s success was down to the strengthening of test-and-trace capacities, for example. “New Zealand was not the world leader in this,” says Baker. “We learned from the Asian experience.” Specifically, Baker and his colleagues followed what had worked in places such as Taiwan, which has reported fewer than 10 deaths to date.

Both New Zealand and Taiwan enforced border controls early on in the outbreak, restricting the arrival of travellers who might bring the virus in with them. Travel restrictions also worked well for Nepal and Sri Lanka, says Chowdhury.

Some countries that didn’t impose such restrictions appear to have suffered as a result. “That has been a key factor in how quickly we saw the local epidemic become a pandemic in Bangladesh,” says Chowdhury.

When outbreaks were hitting Europe and the Middle East, Bangladeshis in these regions boarded flights back to the country. “People were scared and wanted to go to their home country, and a good proportion were potentially carrying the virus,” says Chowdhury. “It was impossible for the local government to screen so many people so suddenly and, as a result, they lost control.”

The first British outbreaks are thought to have been triggered by people returning from skiing holidays in Italy and Austria, and cases also came from China, says Patricia Schlagenhauf, a professor at the University of Zurich, in Switzerland. “It’s obvious that travel does contribute a lot to the spread of the virus,” she says.

However, at the start of the pandemic, the WHO made a point of not recommending that international travellers be screened for infections or travel be restricted in any way. “Later, they did advise against unnecessary travel,” says Schlagenhauf.

Coronavirus travel restrictions will have to give way soon

But travel restrictions and bans are hard to implement and people can always find ways around them, says Hota. Such restrictions aren’t always the best use of resources, either, especially for bigger nations and those that aren’t islands, where the challenge is far greater, says Nuzzo. She highlights the experiences of the US, which banned most non-residents from arriving from China in February. “But there are a lot of people travelling from China to the United States anyway because they are residents of the US,” says Nuzzo.

The public health resources dedicated to managing this small pool of people could have been better imple­mented elsewhere, says Nuzzo. “I had a colleague at a large city health department who said that they had two returning travellers from China who they needed to put into quarantine,” she recalls. “They had 33 staff dedicated to finding them a hotel, monitoring them, making sure their safety was ensured and making sure they didn’t leave,” she says.

“It ate up all of the resources to do things like expand hospital capacity and protect nursing homes and expand laboratory testing,” says Nuzzo. “There was a lot of stuff the US needed to be doing in January, February and early March that it just didn’t do.”

Blocking travel from China didn’t help places like New York. The city’s huge outbreak is thought to have been triggered by travellers bringing the virus from Europe, says Nuzzo.

Face masks and coverings

A better understanding of how the virus spreads is also changing the way we try to tackle its spread. We have learned, for instance, that people without symptoms can spread the virus. This appears to be true of both those who later go on to become unwell and those who never develop any symptoms.

The organisation changed its position last month, and currently recommends that people over 60 and those with underlying health conditions don a medical-grade mask in settings where they are unable to keep their distance from others.

Non-medical masks are also recommended for anyone visiting indoor public settings, such as shops, schools and public transport, as well as those living in cramped conditions, or spending time in areas where there is widespread transmission or where physical distancing is impossible.

How face masks became part of Hong Kong’s identity

Even now, there are no robust, randomised, controlled trials to show that mask wearing in the community slows the virus’ transmission. Sceptics caution that cloth masks vary in their ability to limit the spread of infectious particles – and none will completely prevent transmission. There are also concerns that, outside clinical settings, face masks are often improperly used. Many users continue to touch their faces while wearing face coverings, wear them below their noses or fail to wash them between uses, for example, rendering them much less effective.

Still, scientific consensus has swung in the past few months. Now, most scientists will argue that, as the use of face masks is supported by a handful of small, weak studies, and they don’t do any harm, they are worth using, at least in places where it is hard to keep away from other people. “There’s no reason not to use them,” says Nuzzo.

Despite the lessons learned, many countries remain a long way from eliminating the virus, and a mix of strategies will be required. “I think the goal is to keep the case numbers as low as possible until we get a vaccine,” says Nuzzo.

Text: New Scientist

What we still don’t know about the virus’ spread

 Despite all we have learned about how the coronavirus is transmitted and how best to contain it, plenty of questions remain unanswered.

Mass gatherings

The role that mass gatherings play in the virus’ spread is still unclear. A football match in Milan, Italy, in February is thought to have contributed to the particularly large outbreak that followed in the area. Outbreaks have also been linked to big social gatherings.

Modelling studies suggest that mass gatherings can act as so-called super-spreader events. Yet we still don’t know how important these events have been in the spread of coronavirus, says Rajiv Chowdhury, at the University of Cambridge.

Super-spreaders

More generally, the role of super-spreaders – people who infect a disproportionate number of others – remains unknown. That is partly because researchers and govern­ments have tended to focus on the R number, which indicates the virus’ ability to spread, instead of the K number, which illustrates how much of that spread is due to what proportion of people.

The K num­ber might suggest, for example, that 10 per cent of people are responsible for 80 per cent of infections. “It sheds light on the variation behind R and how much a disease relies on mass gatherings,” says Chowdhury. “It’s something we need to look at.”

Indoor locations

We have learned that being close to someone, indoors, plays a significant role in spreading the coronavirus. But how well venues can manage this risk is still being investigated.

Bars, nightclubs, ski resorts and cruise ships have all been linked to outbreaks. People won’t be covering their faces when eating or drinking and they get close to each other to speak when loud music is playing. Alcohol is likely to lower inhibi­tions regarding social distancing, too.

Schools

We have learned that only a tiny percen­tage of children appear to experience severe cases, but children may still pass the virus on. The evidence from reopening schools is mixed. There have been encoura­ging signs in Europe, but schools in Israel have had to close again after hundreds of students and staff have tested positive.

Text: New Scientist