It’s the biggest question in the world right now: is Covid-19 a deadly disease that only a small fraction of our populations have so far been exposed to? Or is it a much milder pandemic that a large percentage of people have already encountered and is already on its way out?
If Professor Neil Ferguson of Imperial College is the figurehead for the first opinion, then Sunetra Gupta, Professor of Theoretical Epidemiology at the University of Oxford, is the representative of the second. Her group at Oxford produced a rival model to Ferguson’s back in March which speculated that as much as 50% of the population may already have been infected and the true Infection Fatality Rate may be as low as 0.1%.
Since then, we have seen various antibody studies around the world indicating a disappointingly small percentage of seroprevalence — the percentage of the population has the anti-Covid-19 antibody. It was starting to seem like Ferguson’s view was the one closer to the truth.
But, in her first major interview since the Oxford study was published in March, Professor Gupta is only more convinced that her original opinion was correct.
As she sees it, the antibody studies, although useful, do not indicate the true level of exposure or level of immunity. First, many of the antibody tests are “extremely unreliable” and rely on hard-to-achieve representative groups. But more important, many people who have been exposed to the virus will have other kinds of immunity that don’t show up on antibody tests — either for genetic reasons or the result of pre-existing immunities to related coronaviruses such as the common cold.
The implications of this are profound – it means that when we hear results from antibody tests (such as a forthcoming official UK Government study) the percentage who test positive for antibodies is not necessarily equal to the percentage who have immunity or resistance to the virus. The true number could be much higher.
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