People wearing face masks arrive at the Cadorna railway station in Milan, as Italy begins a staged end to a nationwide coronavirus lockdown, May 4, 2020.Flavio Lo Scaldo/Reuters

As cases of the novel coronavirus drop in western Europe, countries including Spain, Italy, Denmark, and Germany have begun to move again.

They're opening up shops, schools, hairdressers, parks, and train stations, adapting to a new normal in a world filled with COVID-19 infections, with varying degrees of caution.

In the US, now the global epicenter of the coronavirus pandemic, several states are also opening back up for business, with people heading back into places like barbershops, bowling alleys, and restaurants, to share the air with strangers for the first time in many weeks. Advertisement

But the World Health Organization warned on Wednesday that such reopenings, if done too quickly or carelessly, could easily prompt a virus rebound.

"The risk of returning to lockdown remains very real if countries do not manage the transition extremely carefully, and in a phased approach," WHO Director General Tedros Adhanom Ghebreyesus said on Wednesday, during a virtual press conference with reporters. "Strong and resilient health systems must be the foundation of recovery in all countries."

Tedros outlined six key criteria that the WHO recommends countries consider when they're weighing whether, and when, the time is right to reopen and reemerge into public space during this pandemic.

He described responsible reopening as ensuring the following:

1. 'Surveillance is strong, cases are declining, and transmission is controlled'

Recent trends suggest that coronavirus case counts may be heading in the right direction on this front in Europe, but not yet in the Americas:

2. 'Health system capacities are in place to detect, isolate, test, and treat every case and trace every contact'

Planning experts at Harvard and Johns Hopkins suggest a safe strategy for this in the US would soon require 20 million coronavirus tests a day, and an army of hundreds of thousands of contact tracers ready to spot new cases, preparedness numbers the country is nowhere near reaching. Advertisement

3. 'Outbreak risks are minimized in special settings like health facilities and nursing homes'

One nursing home near Lyon, France took drastic measures to safeguard its elderly residents during the pandemic, by locking all the residents and staff inside for 47 days straight, an extreme strategy that appears to have worked well at keeping everyone there disease-free.

4. 'Preventive measures are in place in workplaces, the schools, and other places where it's essential for people to go'

Such measures could include plans to stagger when workers head back into their offices this summer, along with more access to healthcare and financial support for people who need to stay home when they become ill or are exposed to the coronavirus.

5. 'Importation risks can be managed'

In China, where near all reported coronavirus cases now originate abroad, there are strict quarantine and testing measures in place for anyone returning to the country, but even those harsh measures don't catch every new case. More hospitals and isolation spaces are being built near the borders, Reuters reported in April.Advertisement

6. 'Communities are fully educated, engaged, and empowered to adjust to the new norm'

The WHO's suggestions rely on major investments in local and state public health systems. The agency stressed that we all need to be better prepared for the next pandemic, so there isn't another rush to "fund panic" again.

"There can be no going back to business as usual," Tedros said. "If we learn anything from COVID 19, it must be that investing in health now will save lives later."