Covid-19 reinfections are real. Should you be worried?

Reports that Covid-19 patients are getting reinfected with the virus shouldn't be surprising, since the disease, like the common cold, is caused by a coronavirus. Even so, it's a troubling development as it is much deadlier, says the writer. PHOTO: AFP/GETTY IMAGES

(BLOOMBERG) - We all suffer multiple bouts of the common cold throughout our lives and never think twice about it. We live with recurring influenza seasons despite a vaccine. But what about Covid-19?

Repeat occurrences of cold and flu happen because our immune systems seem to "forget" the previous infection.

Sometimes, a case isn't serious enough for the body to develop an immune reaction and create a "memory" to help fight it the next time. In other cases, the virus has changed enough such that the immune system does not recognise it and has to mount a brand new reaction. This tends to happen with the flu because it mutates a lot, and that is why vaccines targeting a specific flu strain become less effective as new ones arise.

It is against this backdrop that we hear reports of Covid-19 patients getting reinfected with the virus.

In some ways, this shouldn't be surprising; after all, Covid-19, like the common cold, is caused by a coronavirus. Even so, it's a troubling development, given how much more deadly this virus is relative to most colds and flu, especially in older people and those with health conditions such as obesity or diabetes.

As it is, a wave of fresh outbreaks is causing a spike in new cases worldwide, before any rash of second bouts.

Should we be worried about reinfections?

It all depends, like so much else in this fight, on the development of an effective vaccine.

The good news is that with such an inoculation, Covid-19 will likely be less of a threat even if the virus lingers in one form or another. But there are unknowns.

Here's what we do know: When it comes to Covid-19, at least as of now, reinfections appear to be very rare.

Out of more than 40 million Covid-19 cases reported worldwide, there have been only five properly documented reinfections. That's a rate of 1.25 per 10 million infections.

Reinfections may become more common as time passes. This may happen if our immune systems don't consistently mount a strong or durable reaction to the virus, as is the case for the four coronaviruses that cause the common cold.

Alternatively, the virus could start to mutate sufficiently to allow it to reinfect even individuals whose immune systems do have a memory of it.

The last scenario is less of a worry because Sars-Cov-2 - the virus that causes Covid-19 - is one of the few viruses in its class that has a "proof-reading" mechanism to correct mutations. While this reduces the number of mutations to far below that seen with the influenza virus, it does still happen.

What all this means is, there's a chance that the virus causing Covid-19 becomes endemic in the human population just like flu and the common cold. That, in turn, raises the unpalatable prospect of recurring lockdowns, hospitalisations and deaths.

But here's where a vaccine comes in. We know that the virus is very good at evading the human immune system through multiple mechanisms. So an infection is likely to lead to a suboptimal immune response in most people, especially the more vulnerable older population which has a diminished immune system.

An effective vaccine would help the body put up a better fight against an infection, limiting the severity of any health effects.

More good news: Most of the Covid-19 vaccines now in development target the "spike protein", a part of the virus which has shown little change over time.

Also, the newer types of vaccines like those being developed by Moderna and Pfizer-BioNTech - which use the body's protein machinery to prime the immune system - can be rapidly deployed to produce a different vaccine if the virus mutates enough to evade a current version.

Assuming one or more vaccines make it through to approval, they have a good chance not only of staving off new cases but also limiting the incidence of repeat infections.

They don't have to work perfectly in the most susceptible people, such as the elderly, because a good immunisation campaign in younger individuals will create the "herd immunity" that we all keep hearing about.

If vaccines do not work at all - or end up not inducing a very strong or long-lasting immune reaction - then we are in a very tough spot. As of now, based on limited data, we can only guess at which way it will go.

I remain optimistic that we will get one or more vaccines that can help us manage this disease, including reinfections. But it's too soon to say for sure. That's why I say don't worry - just yet.

Sam Fazeli is senior pharmaceuticals analyst for Bloomberg Intelligence.

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