Thread by @petermbenglish

"Antibody tests offer the hope that people who think they have had the disease will know they are immune and get back to life as normal."

True; but it begs a lot of questions about the nature and duration of immunity.

I would like to know more about this. (Perhaps @PeterKolchinsky can help.)

We obviously know very little about the quality and duration of immunity following Covid-19 infection - it's too soon.

But we can make some guesses based on what we know of other Coronaviruses.

I have read that the duration of immunity following infection with other coronaviruses is relatively short - a few months, perhaps over a year.

But I know enough to know that I don't know what this really means!

Is this a reference to serum antibody levels? Or to actual functioning immunity?

Some antigens and infections do not stimulate a T-cell response, without which immune memory is not formed.

With unconjugated polysaccharide vaccines, for example, there is no "memory", and repeated exposure can lead to immune tolerance, and a poorer antibody response.

With other infections - hepatitis B, measles... - you get immune memory.

With immune memory, circulating B cells are antibody factories, ready to spring into life and rapidly produce vigorous antibody production the moment they detect re-exposure; and killer T-cells are primed and ready to react even if…

…even if serum antibody levels have dropped.

With many diseases, reinfection can occur. Often rarely. Or infection following an initial response to vaccination (secondary vaccine failure). Where there is immune memory, however, such reinfections are often "attenuated"…

…attenuated, because, although the immune system didn't kick in quickly enough to prevent infection, it still prevents most of the harm from the disease. We see this with eg measles and mumps secondary vaccine failure cases.

By contrast, with a few diseases - like Dengue - serious illness arises on reinfection (sometimes with a closely related but not identical virus).

So, given all of this… what is likely to be the case with Covid-19? How long are people likely to be protected after recovery? Will they be completely susceptible to disease, as serious as if they'd never had it before, if reinfected?

Will they have at least partial protection - the sort of protection that might mean they're unlikely to significantly reduce their odds of dying or needing hospital treatment, ventilation etc?

Is there a chance of worse disease, perhaps due to "antibody dependent enhancement"?

Obviously, we don't know the answers to these questions - not for certain, yet. But can we make educated guesses?

@threadreaderapp unroll