Earlier this month, India extended its lockdown for another two weeks amid growing concerns that if nations ease restrictions too soon, the world may well see a second wave of infections.

A second wave is more or less inevitable. "This virus may just become another endemic virus in our communities," said Dr. Mike Ryan of the World Health Organization at a press conference streamed live on May 13. "This virus may never go away."

Ryan, the executive director of the WHO's Health Emergencies Program, pointed out that other viruses like HIV haven't gone away either. Instead, we've developed drugs to mitigate its affects and we've learned to live with it. Only the fewest of deadly viruses, such as smallpox, have ever been eradicated.

The rest live on in the community. Some, like tuberculosis, make a comeback, and history shows that a second wave of a pandemic can be worse than the first. This was the case with the Spanish flu pandemic of 1918, which continued in waves until letting up in 1920.

So, should we be a little more patient? Should we stay in lockdown?

Germany: A controlled experiment?

When the coronavirus reproduction rate R fell from a threshold of 1 down to 0.76 at the end of April, the German government and health authorities agreed to partially reopen schools for those sitting major exams or moving from primary to secondary schools in the autumn.

The schools set about redesigning classrooms and segmenting concrete playgrounds into safe zones, to ensure they met physical distancing and hygiene guidelines.

But before schools and their pupils had a chance to return to class and test those ad hoc safety designs, the government decided to lift restrictions further. Now, even younger children were to return to school, for a day at a time.

Zoos and museums are also reopening with new physical distancing rules, ensuring that people remain apart from each other. But there's no sign of any such rules at playgrounds, which reopened on May 7, and where a physical distancing rule of 1.5 meters (about 5 feet) between kids has quickly dwindled to 1.5 centimeters. Was this a controlled experiment for good behavior? Germany is, after all, a democracy "built on trust," said Chancellor Angela Merkel last week as she announced the relaxed regulations.

The WHO, however, would prefer that the transition from lockdown be "evidence based [and] data driven," one that is "implemented incrementally" to "reduce the risk of new outbreaks."

"Ideally there would be a minimum of 2 weeks (corresponding to the incubation period of COVID-19) between each phase of the transition, to allow sufficient time to understand the risk of new outbreaks and to respond appropriately," the WHO said in its COVID-19 strategy update from April 19.

That has not exactly happened in Germany, with the second phase of the transition for schools starting a mere four days after higher grades went back to class.

The federal government has left it to the states and municipalities to track developments, saying that tighter restrictions should be reintroduced if a region detects 50 new cases of coronavirus per 100,000 people in any given week.

No international standard

But it would appear that there is no agreed standard for what constitutes a second wave of an epidemic or pandemic — either at a global or national, regional level. So, the 50 cases per 100,000 people may be nothing more than a nice round figure.

In an email to DW, WHO spokesperson Christian Lindmeier said the "second wave" is not a fixed technical term. "The term [only] refers to renewed outbreaks after an initial reduction in cases. Hence, the same applies for a 'third' wave."

Some researchers in Germany, including Eva Grill at the Ludwig Maximilian University of Munich and Rafael Mikolajczyk at Martin Luther University Halle-Wittenberg, are reportedly worried that 50 cases per 100,000 people is too high — too high for the health system to cope, or simply too late to stop the spread.

If or when it happens, people will panic and cities will head back into lockdown. Plans for classroom education will tank along with the economy, and everyone will go nuts indoors. Again. We'll be desperate to reemerge, and when the number of new cases drops again, restrictions will be eased once more.

It's a classic cycle. But one with which we may have to learn to live.

"If disease persists in countries at a low level without the capacity to investigate and identify clusters," said the WHO's Mike Ryan at an earlier press conference on May 11, "then there is always the risk that the disease will take off again, particularly where we have large groups of people together in major cities, in refugee camps and other places where people don't have the possibility of large-scale social or physical distancing."

Viruses always mutate and come back

The influenza pandemic of 1918 had three major waves. Starting in March 1918, its peak came during a second wave late that same year.

That second wave was a stronger mutation than the first version of the virus.

In fact, the U.S. Centers for Disease Control and Prevention (CDC) has said the second wave was responsible for the majority of the deaths in the U.S. — the flu's likely country of origin.

A third wave came in early 1919 and lasted until mid-year when, according to the CDC, the Spanish flu "subsided." But it probably never fully went away.

Some virologists suggest that a virus weakens with subsequent mutations. It becomes less fatal for humans, not only because people develop an immunity or resilience to the virus, but also because the virus needs living hosts to reproduce and survive itself. And so, it lives on in the community.

A 2006 study suggested that almost all cases of influenza A — an influenza that affects birds and mammals — since the Spanish flu were "caused by descendants of the 1918 virus."

We're already seeing what may become, officially, a second wave of the novel coronavirus. There are new cases in China, Russia and even South Korea, which has been praised for its containment of the first wave.

As the Northern Hemisphere heads into summer and with Greece and Spain banking on a tourist season despite the virus, we may see that second wave sooner than later, as predicted by a study published in British medical journal The Lancet in April.

"The question is, can we reach a point where we have strong public health measures in place, where we can [detect] clusters of cases and suppress those clusters without going back to the intense transmission patterns of before," said Ryan.

A major wave of new infections would bring a second wave of lockdowns.

"That's what we're trying to avoid," said Ryan. "So, we hope, and we have faith that Germany, Korea and other countries will be able to suppress the clusters they're having and, in some cases, maybe at a subnational level, they may have to impose some specific measures targeted at reducing particular types of transmission."

Or we'll all be rebooking our holidays yet again.