Mutated virus variants can reinfect us

Krishna: Yes, mutated virus variants can reinfect us. Although rare, one can be infected with various variants at the same time.

Reports of reinfection have become common now, especially since the emergence of the omicron variant. Research from South Africa (1) suggests that the risk of reinfection increased quickly and substantially after the variant arrived.

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.

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.

In general, reinfections should be less severe than primary infections, as the person being reinfected will have some pre-existing immunity from their primary infection. If the person took vaccines too, then he will have hybrid immunity which is an excellent in protecting against severe infection. However, data shows the proportion of people reporting symptoms with their reinfection varies depending on what variant they were likely infected with second time round. Reinfections with alpha gave people symptoms only 20% of the time, whereas delta reinfections caused symptoms in 44% of cases and omicron in 46%.

We know that the severity of COVID varies from one variant to another. However, it’s difficult to distinguish how much of the difference above is down to the different strengths of the variants, and how much is due to levels of COVID immunity from prior infection and vaccination present in people at the time.

Footnotes:

1. https://www.science.org/doi/10.1126/science.abn4947