As countries ease lock downs, the worry is that populations remain highly vulnerable.
Will there be a second wave?
How and why multiple-wave outbreaks occur, and how subsequent waves of infection can be prevented, has become a staple of epidemiological modelling studies and pandemic preparation, which have looked at everything from social behavior and health policy to vaccination and the buildup of community immunity, also known as herd immunity.
While second waves and secondary peaks within the period of a pandemic are technically different, the concern is essentially the same: the disease coming back in force.
Corona virus updates
Data correct at 07.25 UTC 21 April
Confirmed cases: 2,472,259.
Is there evidence of corona virus coming back elsewhere?
Without a vaccine, and with no widespread immunity to the new disease, one alarm is being sounded by the experience of Singapore, which has seen a sudden resurgence in infections despite being lauded for its early handling of the outbreak.
Although Singapore instituted a strong contact tracing system for its general population, the disease re-emerged in cramped dormitory accommodation used by thousands of foreign workers with inadequate hygiene facilities and shared canteens.
With 1,426 new cases reported on Monday and nine dormitories – the biggest of which holds 24,000 men – declared isolation units, Singapore’s experience, although very specific, has demonstrated the ability of the disease to come back strongly in places where people are in close proximity and its ability to exploit any weakness in public health regimes set up to counter it.
What are experts worried about?
Conventional wisdom among scientists suggests second waves of resistant infections occur after the capacity for treatment and isolation becomes exhausted. In this case the concern is that the social and political consensus supporting lock downs is being overtaken by public frustration – which has triggered protests in the US and elsewhere – and the urgent need to reopen economies.
The threat declines when susceptibility of the population to the disease falls below a certain threshold or when widespread vaccination becomes available.
In general terms the ratio of susceptible and immune individuals in a population at the end of one wave determines the potential magnitude of a subsequent wave. The worry right now is that with a vaccine still months away, and the real rate of infection only being guessed at, populations worldwide remain highly vulnerable to both resurgence and subsequent waves.
As Justin Lessler, an associate professor of epidemiology at Johns Hopkins University, wrote strikingly for the Washington Post in March: “Epidemics are like fires. When fuel is plentiful, they rage uncontrollably, and when it is scarce, they smolder slowly.
The problem is that we do not know how much fuel is still available for the virus.
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Will There Be a Second Wave Of Coronavirus?
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