1 May 2020
With much journalistic ink spilled over Covid-19 it is easy to forget that our policies of lockdown and social distancing are based on a belief about the lethality of the virus and its spread. This belief comes from interpreting evidence. Currently, two main ideas predominate. Although the government has not stated it explicitly, their elimination policy now indicates that Covid-19 cases are contained, and that the virus can be put back in the box. This optimistic picture starkly contrasts with more convincing evidence from overseas that the virus is now well and truly out of the box, being now much more widespread than first thought. While this initially sounds terrible, it is instead good news, as it allows for a more relaxed stance toward the virus.
The government is now treating the disease in a similar fashion to how we have treated measles. Under this model, the vast majority of cases of infections have symptoms, the test is accurate, and we can contain the virus through contact tracing, quarantine and vaccination. This is a good model for infections that ‘declare themselves’ by causing unequivocal disease in cases and where vaccination is available.
The government has reused this model for Covid-19. Superficially, there is some justification, since community surveys of swab testing for coronavirus have all returned negative. The elimination strategy justifies harsh lockdowns which may be severe in the short term, but pay long term dividends. Under this model, the infection fatality proportion, that is the number of deaths divided by the number of people with infection, is (at the time of writing in NZ) 1.6%, well above seasonal flu (~0.1%), and justifies the ‘eliminate’ approach.
While this may sound attractive, several lines of evidence now indicate the virus often doesn’t ‘declare itself’ like measles, and is instead far more widespread than was initially thought. For example, in Iceland, a community survey of the population showed about 1% of the population tested positive for the virus from a nose swab, and about half showed no symptoms, despite the positive test results.
Information from antibody tests adds to the evidence that the virus has well and truly left the box and left its trail circulating in our bloodstream. After infection, the body mounts an immune response. After exposure, we produce antibodies as evidence that we have seen the virus. This blood test is quite different from the genetic nose swab that has so far dominated New Zealand’s ‘elimination’ thinking. The swab results only indicate the presence of the virus at the time the test was taken.
Antibodies give a contrasting picture from nose swab tests. Varying percentages of positive antibodies are reported, but the overwhelming picture is that many more people have recovered from the virus than has been appreciated. The percentage varies between 4% (Santa Clara, California) to 21% in New York city.
Why is this good news? Well, it indicates that exposure to the virus is about 50 to 85 times that observed from nose swab tests alone. In turn, this information dials back New Zealand fatality estimates to about 0.03% of all infected cases. This adjusted mortality rate is no greater than that for seasonal influenza. This is an important reality check on modelling figures which forecast carnage from Covid-19 equivalent to World War I deaths.
These antibody surveys are from overseas, and critics may argue that this does not apply to our New Zealand Covid-19 situation. Features of our Covid-19 cases, however, support the ‘out of the box’ idea. For example, in the recent measles outbreak, sourced from overseas, the majority of cases occurred in Auckland. For Covid-19, however, cases are much more dispersed around New Zealand, with 3% having no apparent link to overseas sources or other cases (44/1,461). In an effort to stamp the virus out, we will be hunting for needles in a very large haystack.
Since the disease is much more widespread than initially thought, then lockdowns are also unlikely to be effective at reducing spread. Recent evidence supports this idea. A comparison of US States showed that regions with social distancing were doing as well or even better on average for Covid-19 case or death rates than those that had a lockdown policy. Per capita cases and death rates were largely determined by a State’s population density – a factor New Zealand has on its side. While it is tempting to compare ourselves with New York, we have a population density more similar to Vermont, Arkansas, Oklahoma and Iowa. States with these population densities have death rates 95% lower than in New York, and are almost identical whether or not the State has locked down.
The government’s idea of a contained virus simply doesn’t gel with recent antibody surveys. The idea of elimination is scientifically unsound. The weight of evidence clearly illustrates that we are dealing with a virus that is more widespread and much less deadly than we feared. Evidence strongly supports us throwing off the lockdown shackles, safely returning to work and school, while doing our utmost to protect our most vulnerable in hospitals and rest homes.