The reason everyone should have expected occasional error in the quarantining of overseas arrivals is one of many reasons not to lockdown again. The whole point of quarantine is to catch positive cases.
The Prime Minister should have primed the debate better months ago. Instead she boasted of having eliminated the virus. She set herself up for a fall and may even cost herself the election.
A few returnees will be picked up as Covid-19 positive between now and when a vaccine is available and is widely applied worldwide. That day may never come.
Maybe there will be a vaccine and we will reach community vaccination targets high enough for herd immunity. But we struggle to reach winter vaccination targets for senior citizens with multiple health conditions, much less with all annual vaccination targets among the old and middle-aged.
The upside of the positive cases in quarantine from now probably to the end of time is a false sense of security was dashed. This will double or treble the number of young people who will vaccinate.
The experience with Victoria just unable to eliminate the virus and in Florida of an explosion of infections after reopening suggests locking down was always an initial stopgap to flatten the curve.
Flattening the curve was supposed to mean not overwhelming the hospital system and leave it badly short-staffed because of many infected medical workers having to go into quarantine themselves.
The net lives saved from the lockdown is now known to be ambiguous because 400 additional deaths are expected by the NZ Cancer Society from a three-month delay in treatment and diagnosis.
There were nearly 10,000 excess deaths from dementia in the UK not from Covid-19 in recent months. Disrupted routines of dementia patients and staff shortages let their health fall away. The old must be reminded to drink because of a reduced sensation of thirst. The loss of family visits caused confusion, refusals to eat and loss of the ability to communicate. One in three British paediatricians are handling emergency admissions who turned up later than usual.
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Covid-19 appears to be mostly spread by maybe 10 per cent of the infected; by super spreaders or in confined environments ranging from meat works and subways to choir practices.
Neighbouring provinces or countries can lockdown equally hard; one can be New Zealand, the other Lombardy, depending on how unlucky they are with super spreaders cropping up here there and everywhere. We were plain lucky to not have super spreaders before the borders were closed.
More data is in on what works. Ciminelli and Garcia-Mandico found that shutting non-essential in-person services greatly reduces deaths but closing factories does not. Death rates were much the same in the average Italian municipality and those with 10 per cent higher shares of factory employment.
Analysis of wastewater may give us a seven-day heads up on infection rates. If so, the Italian analysis suggests that alert level 2, and at absolute most, alert level 3 is enough.
Data in many countries shows that most of the required social distancing occurs two weeks or so before any government action because of people fearing infection. Many stop going out and work and shop from home.
Further waves are inevitable. It just takes one super spreader among aircrew or after a quarantine botch up. Another alert level 4 lockdown is unaffordable but nor do we need it.
Alert level 2 social distancing may have curbed infections in Italy by as much as their level 4 lockdown.
• Economist Jim Rose blogs at utopiayouarestandinginit.com