As countries ease lockdowns, the concern is that residents remain highly vulnerable

With more countries planning to ease restrictions imposed by the Coronavirus, but British Prime Minister, Boris Johnson, and German Chancellor, Angela Merkel, are concerned about the possibility of a resurgence or a second wave, here is what we know from the rest of the world about the risk of a resurgence of Covid-19.

Will There Be a Second Wave?

Infectious disease epidemics behave in different ways, but the 1918 influenza pandemic that killed more than 50 million people is seen as a prime example of a pandemic that occurred in multiple waves, the latter more severe than the first. It was repeated – albeit in a less mild manner – in subsequent influenza epidemics.

Other influenza epidemics—including in 1957 and 1968—have all had multiple waves. The 2009 H1N1(a) influenza pandemic began in April and was followed, in the United States and in the diverse Northern Hemisphere, by a second wave in the fall.

How and why multi-wave outbreaks occur, and how subsequent waves of infection can be prevented, has become a staple in epidemiological modeling and pandemic preparation studies, which have looked at everything from social behavior and health policy to vaccination and building community immunity, also known as herd immunity.

While second waves and secondary peaks during a pandemic period are technically different, the concern is essentially the same: disease returning to strength.

Is There Evidence of Coronavirus Coming Back Elsewhere?

This is monitored very carefully. Without a vaccine, and without widespread immunity to the new disease, one alarm stems from the experience of Singapore, which has seen a sudden rebound in infections despite being lauded for its early handling of the outbreak.

Although Singapore has established a robust contact tracing system for its general population, the disease has resurfaced in cramped housing used by thousands of foreign workers with inadequate hygiene facilities and communal canteens.

With 1,426 new cases reported on Monday and nine dormitories – the largest housing 24,000 men – declared isolation units, Singapore’s experience, while very specific, has demonstrated the disease’s ability to make a strong comeback in places where people are in close proximity to one another. Its ability to exploit any weakness in the public health systems is set up to counter it.