As nations lift lockdowns and experts worry about a potential second peak in cases, our ability to ward off infection is one of the hottest topics of scientific debate.
Ever since it became apparent that children were less vulnerable to COVID-19 early in the pandemic, scientists have speculated that the regular spread of benign viruses in places like schools could have bolstered their immune response to the latest coronavirus.
Now the idea of “cross immunity” among the broader population is gaining some ground.
In a recent post on Twitter, Francois Balloux of University College London noted an “intriguing” lack of an immediate resurgence in COVID-19 cases following the easing of lockdowns in several countries.
Among the possible explanations, he noted, were seasonality and enduring social distancing practices.
But he posited a “wilder” hypothesis as well — that a “proportion of the population might have pre-existing immunity to #SARSCoV2, potentially due to prior exposure to ‘common cold’ coronaviruses”.
Balloux said that might explain issues like cases where there is no transmission between spouses.
Earlier this month, an American study in the journal Cell suggested between 40 and 60 percent of the population could be immunized against COVID-19 without ever being exposed to it.
Researchers put this down to the action of protective cells, known as T lymphocytes, that had been activated by other coronaviruses responsible for colds.