Among the many medical puzzles about COVID-19 that continue to confound experts: Why does one spouse contract COVID-19 while in many cases the other does not? Why does the African continent have far fewer COVID-19 cases and deaths per capita than the other continents? Why does Singapore have more COVID-19 cases per capita than the U.S. but less than one-tenth the per capita death rate? What protects better from future COVID-19 infection, previous infection or vaccination?
Some of the partial answers to these questions are obvious: In terms of prevention, both previous infection and vaccination protect better than either alone. Environmental factors and mitigation efforts play a role in how the virus spreads, while age, obesity and underlying health affect COVID-19’s severity. The novel characteristics of the virus and its variants — transmissibility and lethality — surely matter, as does chance, which invariably exerts itself in most medical mysteries.
But the real key to demystifying the COVID-19 pandemic is immunity — explaining why some individuals are able to resist infection, while others are susceptible, and still others are especially vulnerable. Unfortunately, even our best immunologists have little more than a rudimentary understanding of how immunity in COVID-19 works.
