Deciphering New Zealand's COVID-19 numbers

Opinion: Will there be 20 deaths, or 27,000? Virus mortality projections offer Kiwis very different outlooks - Robert Bartholomew explains the the missing variables that could determine which of these predictions will become our reality.

Compare these two projections: One scenario has as many as 27,600 Kiwis dying from COVID-19 –a frightening prospect. On the other end of the spectrum, the best-case scenario from epidemiological modelling places the figure closer to 20. While the worst-case scenario is chilling and citizens should continue to follow the advice of their government and not let their guard down, it is important to look at these figures within the context in which they were drawn up, and not be discouraged by the high numbers. While any responsible government would be remiss if it did not model potential scenarios, mortality projections are fraught with challenges. Producing accurate figures at this point in the pandemic's timeline poses special difficulties because key information is still missing, and these variables are crucial to efforts to create accurate models.

Obviously, there is a massive difference between 20 and 20,000+ deaths. Epidemic outcomes are notoriously difficult to predict. During the SARS outbreak of 2002-03, there were projections that Severe Acute Respiratory Syndrome would be worse than the AIDS epidemic and could kill tens of millions globally. SARS eventually sickened 8,098 people and led to 774 deaths. In 2012-13, there were fears that MERS or Middle East Respiratory Syndrome would become a pandemic. With a death rate of 35 percent, that would have been catastrophic. Similar overestimations were made for Ebola, Swine Flu and the Zika virus.

A Crucial Missing Variable

Models for what could happen in New Zealand will remain fluid and depend on such factors as the development of new drug treatments, potential breakthroughs on the vaccine front (a vaccine is likely; the key question is timing), and new information about mitigating the spread. Some variables which would lead to a worse outcome seem less likely, such as hospital staff going on strike.

But amidst the variables is one missing piece of the coronavirus puzzle that continues to hang over New Zealand and the rest of the world like a dark cloud, shrouding our view of the future: the true mortality rate.

Thus far, this has not been possible to ascertain because so many people have not been tested, so we simply do not know how many infections are out there. A high number of unknown infections could translate to a lower death rate—potentially much lower. As of the time of this writing, Italy has a mortality rate of over 11 percent, while Germany’s rate is just under 1 percent. There is reason for optimism in the numbers because in Italy, most of the deaths are in the north, which has the worst air pollution in Europe. Another factor may be that Italy is the center of the European anti-vaccination movement, as elderly Italians who have been fighting off the flu would also be at greater risk of dying of COVID-19. Italy also has one of the oldest populations in the world.

Another significant reason for the high Italian death rate may be the way their government codes deaths. Italian Health Ministry advisor Walter Ricciardi has noted that their coding of coronavirus deaths is relatively inclusive in that people who die with COVID-19 are typically "deemed to be dying of the coronavirus.” However, when the Italian National Institute of Health recently re-evaluated the situation they found that "only 12 percent of death certificates have shown a direct causality from coronavirus, while 88 percent of patients who have died have at least one pre-morbidity—many had two or three”. Researchers also think the Italian mortality rate is so high because of an exceptionally mild flu season which increased the pool of vulnerable people.  

But if the mortality rate in Italy is sky high, why is Germany's so much lower? While Italy has been focusing their testing on those who are most sick, Germany has been testing those with mild symptoms, regardless of age. Perhaps the most important piece of information that may determine the future course of this pandemic is the conclusion drawn by a World Health Organisation study: 80 percent of patients were either asymptomatic and showed no symptoms or they were so mild they did not realise they had the virus. While these people are carriers, if these findings continue to hold true, mortality projections could drop precipitously.

A major factor in the country's mortality outcome will be how many Māori are affected. During the Great Flu Pandemic of 1918, European Kiwis had mortality rates several times less than Māori. A key factor was their living in rural areas that were unaffected by a milder flu wave earlier that year, that would have provided some immunity. Poor living conditions and high rates of malnutrition and tuberculosis tied to their loss of land and inferior housing also contributed.  

The modelling of potential deaths in New Zealand – be it 27,600 or 20 – offer very different visions of the future. What these figures show is the importance of taking the outbreak seriously, practising social distancing, good hygiene, and dobbing in people who are flouting the rules.  

Kiwis are not passive, powerless victims. We can exercise some control over which number eventually materialises. We can all help to rewrite the script by doing our part.  

Robert Bartholomew is an Honorary Academic in the Department of Psychological Medicine within the University of Auckland's School of Medicine. He specialises in social panics, popular delusions and mass suggestion.

This article reflects the opinion of the author and not necessarily the views of the University of Auckland.

Used with permission from Psychology Today, COVID-19: A Best-Case Scenario, 24 March, 2020.

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