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Could over half of the UK population have been exposed to the novel coronavirus responsible COVID-19 since January? That’s the figure some British press is reporting, based on a controversial new model created by the University of Oxford. If accurate, that would optimistically suggest that a substantial portion of the UK population has already been infected by the novel coronavirus SAR-CoV-2 and acquired some protective immunity.
However – and it’s a big “however” – many infectious disease experts have urged for extreme caution when interpreting the report, suggesting it makes too many assumptions and could be “open to gross over-interpretation by others.” Regardless of conclusions drawn from the model, the advice remains the same: stay at home, avoid unnecessary physical contact with other people, and wash your hands.
The unpublished paper – a draft of which can be read here (PDF) – used a Susceptible-Infected-Recovered (SIR) model to work out how many people might have been already exposed to COVID-19 in the UK and Italy. Out of three simulated scenarios, one concluded that up to 68 percent of people may already have been exposed to infection between mid-January and March 19, 2020.
This suggests that the number of “hidden cases,” in which people are asymptomatic or only display mild symptoms, could be much higher than the number of confirmed cases suggest. By their workings, there could be over 1,000 people exposed to COVID-19 for every death that’s confirmed. This suggests that the current wave of infections in the UK and Italy could last between 2 to 3 months.
“Importantly, the results we present here suggest the ongoing epidemics in the UK and Italy started at least a month before the first reported death and have already led to the accumulation of significant levels of herd immunity in both countries,” the study reads.
But epidemiology experts are warning there are too many caveats to draw conclusions from all of this. For one, the report attempts to infer infection rates without using any direct data gathered from serological surveys and COVID-19 tests. The study is also not yet peer-reviewed, meaning it has not gone through the rigorous evaluation of others in this field to see if the results can be replicated or stand up to criticism.
“The exact figures must be viewed with caution. The analysis is based on an abstract model which does not account for spatial distribution of infection, and neither the countries in this analysis (Italy or Great Britain) has presented an even geographic distribution of infection,” said Professor Rowland Kao, Chair of Veterinary Epidemiology and Data Science at the University of Edinburgh.
"In my view, the model presented by Lourenço and colleagues suffers from a number of key failings which make me doubt its utility," added Professor Paul Hunter, Professor in Medicine at the University of East Anglia in England. “My main criticism is that a very simple SIR model that assumes complete mixing of the population which is almost always wrong at a country level. We do not all have an equal random chance of meeting every other person in the UK, infected or otherwise.”
It's unclear why the research was shared on Twitter by the researchers in the first place. According to the post, the research will soon appear on the distribution server medRxiv, itself a pre-print site for unpublished or not yet peer-reviewed research in medical, clinical, and related health sciences.
In the wake of the COVID-19 pandemic, many researchers are publishing their work while awaiting peer-review in order to share resources with other scientists and researchers, as well as to broadcast potentially vital information into the public sphere as quickly as possible. While it doesn't necessarily mean the work is false or poor quality, it does mean the results should be interpreted with restraint.
The report does, however, highlight one point that everyone can agree one: if we want to understand and defeat this virus, we need more tests. In the words of Dr Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, last week: “You cannot fight a fire blindfolded and we cannot stop this pandemic if we don't know who is infected. We have a simple message for all countries; test, test, test.”
