July 2020 Update
The above article was written and published back in March 2020. Since then there have been mixed experiences around the World. In the UK, Sweden and parts of the USA the 'let it rip' and go for 'herd immunity' strategy was either deliberately chosen or chosen by default due to an initial reluctance to impose the necessary restrictions.
As of July 18 the UK had 666 deaths per million of population; Sweden had 556 deaths per million and the USA, where some States acted faster than others, there were 420 deaths per million.
It was notable that these three countries were reporting significantly different numbers of cases per million. The USA was reporting over 11,000 cases per million; Sweden over 7,000 while the UK, with almost 60% more deaths than the USA per capita, was reporting only 4,320 cases per million. Clearly the UK is wildly under-reporting case numbers, presumably due to insufficient testing.
At the other end of the Government response spectrum, New Zealand with over a thousand Covid-19 cases, and 21 related deaths in May, closed its borders and locked-down hard. There have been no deaths since. The PM, Jacinda Ardern, announced an elimination strategy. But although they are almost clear they are still finding, on average, one new case a day - so they have suppression - not elimination.
Likewise, Australia was approaching a high level of suppression and several smaller states mirrored the New Zealand experience.
This level of suppression was sufficient for a cautious reopening of cinemas; pubs; bars; clubs; gyms; restaurants; schools and other places of employment across the country without encountering an upsurge in community spread. The economy, nevertheless has taken a significant hit and remains handicapped by the a strict quarantine of visitors and a consequent loss of international tourism and some services, like overseas education.
But in Australia a breach of quarantine in Melbourne, around June 23, led to a surge in cases in Victoria; and delays in responding led to a brief period of uncontrolled spread. This became so concerning that on July 8 the NSW- Victorian border was closed. But not before a Melbourne man had visited a crowded pub in Western Sydney and initiated a new spread, creating 'hot spots' across the metropolitan area and south to Bateman's Bay.
In this there are echoes of 1919 when the Spanish Influenza got loose after a breach of quarantine in Melbourne. As a result of this recent breach much of Melbourne has again been locked-down, with almost three thousand active cases detected, 31 in intensive care; and there have been a handful of additional deaths (to 38 total) in Victoria.
Yet overall, Australia, like New Zealand, has, to date, suffered less than 5 deaths per million of population.
This is all very well in the short term but the unenviable choice, raised back in March, remains. If there is no effective vaccine soon, is the economic hardship currently being imposed by lock-downs worse than the alternative?
The answer depends, as it did at the outset, on how many lives countries are willing to sacrifice in the interests of the economy. Because we can't continue like this indefinitely and if we try to achieve herd immunity without a vaccine we are looking at a repeat of the Spanish Influenza when an estimated 1% of the world population died.
There's an interesting article published by The Centre for Evidence-Based Medicine at the University of Oxford: “When will it be over?”: An introduction to viral reproduction numbers, R0 and Re that attempts to estimate the levels of infection (or inoculation) at which 'herd immunity will be obtained. The authors conclude that: "...to protect us against future epidemics, herd immunity of around 62% will be needed... [yet] taking the highest [R0] value (4.6), 78% immunization [from vaccination or exposure to the virus] will be needed, and it would be wise to aim for at least that."
In other words, to reach herd immunity we need to have between 620,000 and 780,000 cases or inoculations (employing an effective, safe, vaccine) per million people.
The case-fatality rate (CFR) of Covid-19 turns out to be around half that of the Spanish Influenza that had an estimated CFR of around 2.5% (Taubenberger and Morens). The CFR in Australia and New Zealand is around 1.4% and a Lancet Infectious Diseases study, found the median CFR was likely to be 1.38%; slightly lower for the young but much higher for those over the age of 80 or for people with underlying disease (13.4%).
Simple mathematics tells us that if herd immunity is to be reached by infection alone (in the absence of an effective vaccine) between 8 and 11 thousand people will die for each million of a country's population (1.38% of 620 thousand to 780 thousand). At the moment the worst infected country, judging by deaths per million, is Belgium with 845 deaths per million. Yet on these numbers even Belgium is only 10% on the way to achieving herd immunity.
Without a vaccine the USA with a population of 331 million could look forward to another 2.9 million dead, in addition to the 140,000 dead to date. The UK to a further 550,000 dead.
In Australia and New Zealand we have virtually no herd immunity. So if it gets loose in Australia before we have a vaccine we can expect up to 225,000 deaths.
In China, which after the initial disaster, pushed the reproduction rate down to close to zero and has relentlessly traced and suppressed every outbreak since, there is even less residual immunity than in New Zealand. If it get's away there, with a population of 1,439 million, some 13 million will die.
As I write, the virus is indeed spreading in India, with a population 1,380 million. The number of deaths is still relatively low but is doubling every 28 days. As in other less developed countries this is huge disaster in the making.
For more information on viruses see my article: The Chemistry of Life.