Reinfection

[shpalman]

COVID reinfections: are they milder and do they strengthen immunity?

So why are reinfections increasing? The simple answer is because our immunity is often no longer sufficient to prevent an infection. This can be due to the appearance of a new viral variant like omicron that, because of mutations to its form, is less recognisable to the immune system, meaning the virus bypasses prior immunity. Or it can be because immunity has waned since we were last infected or vaccinated. We know that this is a particular issue with COVID immunity – hence the need for vaccine boosters.

Plus, as I have discussed previously, the coronavirus almost always enters the human body via the nose and throat. Immunity in the mucosal linings of these areas tends to be relatively short lived compared to systemic immunity throughout the body. This may explain why protection against severe illness, usually rooted in the lungs, lasts longer than protection against infection.

In a small omicron outbreak in a US household, one unvaccinated person caught the virus for the first time and four unvaccinated others for the second. The illness of the person experiencing the virus for the first time was more severe the illness of those reinfected – but the very small number of cases precludes any firm conclusions.

On the other hand, there have been opposing reports in the past of more severe disease being caused by reinfection.* So while it’s plausible that reinfections should be milder, at the moment, we’re still lacking robust evidence that proves this.

* - fixed their link but it's to MDPI.