Like a giant tidal wave, the COVID-19 pandemic is hitting health systems in several European countries, causing experts to struggle to know when it will peak.
What will be the consequences of this 'tsunami', as it was called by Italian health workers? A general retreat and a return to normalcy, or regular relapses that will overwhelm hospitals?
The calm before the storm?
It looks like the tide has already died down in China, where the coronavirus first emerged late last year: no new cases have been reported in recent days.
But French public health specialist and epidemiologist Antoine Flau of the medical journal The Lancet wonders if things will get worse.
So far, China may have “experienced the messenger wave, using terminology borrowed from those studying tsunami, and is there a big wave yet to come?” he wrote.
To understand the complexity of the evolution of epidemics, it is necessary to go back to the post-World War I period, when the Spanish flu killed nearly 50 million people in three waves – more than the war itself.
After the epidemic stopped.
The question of why this happened was investigated by mathematicians. In the late 1920s, Scottish mathematicians William Ogilvy Kermack and Anderson Gray McKendrick developed models to understand the dynamics of epidemics.
Immunity threshold.
Kermak and McKendrick found that the epidemic does not end because it runs out of vulnerable people, but because as the number of infections increases, the so-called herd immunity threshold is reached.
“Herd immunity is the proportion of people immunized against the virus (either recovering or being vaccinated when it exists) that must be achieved to stop any risk of recurrence,” said Flao, head of the Institute for Global Health at the University of Geneva.
This proportion depends on the ease of transmission of the virus to a healthy person.
The more contagious the disease is, the greater the number of people immunized must be to stop it.
For COVID-19, “there must be 50 to 66 percent of people infected before people become immune to the pandemic,” he said.
The infection rate itself is subject to fluctuations depending on the preventive measures taken, such as quarantine, isolation, and potential weather conditions.
If an infected person infects, on average, less than one person, the epidemic is over, he said.
Recovery.
But this will not necessarily mean the end of the epidemic, which may just take a break, as he argues that “this is currently happening in China and South Korea.”
Because public health measures during an epidemic are temporary, and when you weaken them, the epidemic starts over again until society reaches immunity, sometimes for months or years, 'he said.
The head of the infectious disease service at the Pitie Salpetriere hospital in Paris, Professor François Brixer, also warned of possible 'relapses'
“COVID-19 re-emergence is possible eventually with a seasonal spike,” he said.
Sharon Levin, an Australian infectious disease expert, also wonders about the possibility of a return: 'Will the coronavirus return? We do not know'.
However, she said, SARS (Severe Acute Respiratory Syndrome), also a coronavirus, has completely disappeared due to strict social distancing measures following an epidemic in 2002 and 2003.
The development of a vaccine and its global distribution, which the pharmaceutical industry has promised to deliver within 12-18 months, will radically change the outlook.
Sources: Agence France-Presse. Photo: (Statista / CC BY 3.0)
