Mild dose of Covid virus may boost protection for those vaccinated, says immunologist

The protection vaccines give against Covid-19 may be boosted through exposure to a mild infection with the virus, according to an Irish immunologist. For people who are vaccinated, an asymptomatic or mild dose of SARS-CoV-2 may induce potent mucosal immunity and boost their vaccine effect, according to Prof Mary Keogan of Beaumont Hospital.

Prof Keogan said it was “highly unlikely” additional doses of vaccine would reduce mucosal responses and, therefore, prevent all infections and transmission. Mucosa refers to the lining of organs and body cavities through which viruses can enter.

"We have to weigh up additional vaccine doses extremely carefully," she told a symposium in the Royal College of Physicians in Ireland on Thursday. "We know two doses of vaccine provide protection against severe disease in the vast majority of the population. We don't know if a three-dose schedule will improve response or durability of the protection we get."

“At a time when most of the world is not vaccinated we really can’t afford that luxury,” said Prof Keogan, adding that “we need to be mindful of our responsibility to use this precious resource prudently”.

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The world is currently at the “end of the beginning” of the pandemic, she said, and would only get to the “beginning of the end” when the global population was vaccinated.

To get there, aside from global vaccination, those who were not vaccinated needed to be provide with information about their unanswered questions, she said.