South Korea says it has a second wave of coronavirus infections — but what does that really mean?
Social distancing and lockdowns have created substantial economic losses across the world — but with many countries now easing restrictions, fear is rising about the risk of a second wave of infections.
- Some experts are reluctant to use the term “second wave”
- It is used to refer to a sustained increase in virus cases
- Some countries are using the term while others are avoiding it
South Korea has had to put restrictions back in place after a large spike in cases in the capital Seoul. Earlier this week officials announced the country was experiencing a second wave.
However some are reluctant to use the term, and despite it coming up in conversations about the pandemic so frequently, “second wave” is not an epidemiological term and it is not easy to define.
A case in point: despite Seoul saying it believed it was going through a second wave, a World Health Organization (WHO) representative declined to repeat that suggestion when discussing the situation in South Korea yesterday.
So what actually constitutes a second wave of coronavirus infections? And if South Korea’s experiencing one now, which countries are likely to to be next?
Read more about coronavirus:
What even is a second wave?
According to Marc Lipsitch, director of the Centre for Communicable Disease Dynamics at the Harvard School of Public Health, there is no agreed definition for a second wave — it simply refers to a sustained upsurge in cases.
“A wave is just a metaphor. It is not a term with a precise definition in epidemiology, but it is a useful metaphor indicating that from whatever level of daily new case incidence we have, there is an increase,” he told the ABC.
He said this rise was hopefully followed by a decrease that could be attributed to control measures, seasonality, the accumulation of immunity in the population, or a combination of all those factors.
With viral infections such as influenza or the common cold, cases typically crest in the cold winter months and recede as warmer weather reappears.
Hence the wave metaphor — it’s supposed to go up, peak, and come crashing down.
Unfortunately the reality of what happens during an epidemic isn’t quite as elegant as that, and the metaphor is actually a bit clunky: waves in the ocean always come down, but waves of infectious disease are less reliable.
A second wave is also different to a “spike” in cases — another frequently used term.
“A spike [or upsurge] is a momentary phenomenon,” Professor Lipsitch said.
“But since cases are the cause of more cases, the difference is whether that spike is contained through control measures or allowed to continue through chains of infection.”
According to Australia’s Department of Health, second waves of infection can happen when contact tracing fails, making it harder to control the spread of the virus.
So if you get a temporary increase in infections, that’s a spike — if that uptick continues for a while and is not contained, that’s possibly a second wave.
Which countries are going through a second wave?
While there’s no formal definition for a second wave, some experts say they know it when they see it.
“It’s often quite clear; you’ll see a rise involving a second group of people after infections in a first group have diminished,” epidemiologist Jessica Justman of Columbia University’s Mailman School of Public Health said.
South Korea says it’s going through a second wave of infections at the moment, but it may not be alone.
Mr Lipsitch said the US was also experiencing a steady upsurge in some states, despite the country as a whole going through “a long period of near-flat activity”.
This is because cases are declining in former hotspots such as New York and Washington, but rising dramatically in places such as Texas, Florida and California.
Whether this constitutes a second wave or not is contested, and it’s probably a bit of a pointless argument — again, a “second wave” isn’t an epidemiological term, it’s just a metaphor for a sustained increase in infections.
US officials have not labelled the current situation as a second wave.
Anthony Fauci, America’s top infectious diseases expert, last week said the country was still going through its first wave.
“You can’t talk about a second wave in the summer because we’re still in the first wave. We want to get that first wave down. Then we’ll see if we can keep it there,” Dr Fauci told the Washington Post.
Not everybody is avoiding the term though — Israeli military authorities said in a report released over the weekend that the country was going through a second wave, following a recent uptick of cases in Israel.
And Australia’s own Chief Medical Officer Brendan Murphy has previously said a large second wave would be “the most worrying thing of all” for him.
There are also concerns the current increase in cases in Victoria could lead to a second wave — although according to Professor Tony Blakely from the University of Melbourne, there would need to be more than 1,000 cases before that happened, and we’re not there yet.
Singapore has also gone through what some have described as a second wave of infections after outbreaks at dormitories housing the city state’s large migrant worker population led to a dramatic rise in infections in late April.