The effects of Covid-19 on the immune system and how this affects subsequent infections

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Cecilia*, an Australian woman, has been feeling unwell for much of the year.

After recovering from Covid in April, she suffered a handful of colds over the winter.

“I felt like I’d get over one before the next vaccine hit,” said the mother of two who had three vaccines in Melbourne.

“It was really hard for a while.”

At the end of October, her eldest son was Covid positive. Right after that, so did Cecilia.

“I couldn’t believe it. It feels like there is no end.”

Infections in the immediate aftermath of Covid-19 are common, whether it’s another stint with the SARS-CoV-2 virus or an entirely different pathogen.

It’s not entirely unexpected, according to Paul Griffin, an infectious disease physician and microbiologist at the University of Queensland.

“In other viral infections, sometimes [a person] There may be a slightly higher risk of getting additional infections or reactivating a latent infection.

“For example, some people may have recurrent cold sores if they have a nasty viral infection.”

Moreover, the current round of Omicron subvariant ‘soups’ means that antibodies generated in the face of one infection may not necessarily provide long-term protection against other subvariants.

But why some people seem more susceptible to reinfection and other illnesses after Covid is complicated, Dr. Griffin said.

“A lot of factors come into play,” he said.

“Our immune systems are different at baseline, and as we are exposed to different things, the difference increases.

“For example, we know that past exposure to other viruses may be related.

“So some immune systems are overactive, while others are not fully capable of protecting against certain types of infections.”

What Does Covid-19 Do to Your Immune System?

Simon Barry, a molecular immunologist at the University of Adelaide, says the SARS-CoV-2 virus tends to spread through the lungs, but can wreak havoc throughout the body.

This is because the ACE2 receptors that the virus hooks and uses to infect are not just in the lungs, but everywhere from the intestines to the blood vessels.

Our immune system springs into action to fight these infections. There are different cells working in different parts of the body trying to get the virus out.

And even if you feel recovered after an attack of Covid-19, your immune system still seems to be recovering.

Professor Barry was part of a study published in January that measured different types of immune cells in people hospitalized with the Delta variant over a six-month period.

“Generally, most people experience a great many changes immediately after being infected with the novel coronavirus, which then slowly normalizes over the course of three to six months.

“But there are some subtle immune changes that appear to persist over time.”

They found that one type of immune cell called T cells was the slowest to return to normal.

“T cells are where you get the immune memory response, which is important the next time you encounter the virus. Knock it out before you get symptoms, or knock it out quickly so you don’t get as many symptoms.”

Similar studies have found that other immune cell populations do not revert quickly.

These changes aren’t necessarily numbers, but changes in how immune cells work, said Professor Barry.

“The classic thing in immunology is that the number of cell types of interest doesn’t change…but if you look at what they do, you can actually see that they’re reprogrammed. .”

So immunologists like Professor Barry are figuring out how Covid-19 alters the functioning of our immune cells and alters the knock-on effects in the body.

“We followed up and asked what the real functional impact of having Covid inside individual immune cell types is? How do they talk to each other and that causes disease states? Huh? Is that something we need to fix?”

Why are some people more likely to get Covid multiple times?

Once considered relatively rare, reinfection with Covid-19 now occurs in only one in ten cases, with some people getting four or more infections.

In July, Australia’s Chief Health Protection Commission, which provides advice during health emergencies, changed the Covid-19 “reinfection period” from 12 weeks to 28 days. something new.

So who is more likely to be infected with Covid-19 more than once?

According to a Saudi study investigating Delta reinfection, those exposed to the virus, such as health care workers, are clearly more likely to be reinfected, as are people with HIV, diabetes and obesity.

Older or immunocompromised people, whose immune systems may not be strong enough to fight subsequent infections, are also at increased risk.

But doing all the things that have been hitting us since the pandemic began, regardless of work or physiology, can reduce the risk of reinfection, Dr. Griffin said.

“We know people can get re-infected with Covid, and we cannot assume that re-infection will not cause problems.

“So it’s still worth trying to do what you can to prevent any transmission, and the best way to do that is with a few simple strategies to reduce your risk, like social distancing and wearing a mask. and to stay up to date on vaccines.”

Having “hybrid immunity” (prior infection and vaccination) appears to provide better protection against reinfection from Omicron variants, at least for some time.

For example, a Danish study found that a combination of previous Omicron infection and three rounds of the mRNA Covid vaccine gave people a high level of protection against subsequent BA.5 and BA.2 infections.

Study during Canadian BA.2 epidemic reveals that HCWs who received two doses of mRNA vaccine and were previously infected with BA.1 were protected from ‘long-term’ BA.2 reinfection became.

Cecilia is keen to get her 4th dose in the New Year, in line with recommendations from the Australian Technical Advisory Group on Immunization.

“We will do everything we can to reduce the chances of catching Covid, or even getting sick, as much as possible.”

*Name changed to protect privacy

-ABC