Why Some People Get COVID More Than Once


Although the federal government does not collect data on COVID reinfections, and nor do health authorities in WA and Queensland, Victoria recorded almost 10,000 reinfections between late December 2021 and late March 2022. This compares with just 108 known reinfections in Victoria during the previous two years. NSW plans to release state reinfection data soon.

As the Omicron sub-variant BA.2 continues to fuel more infections, the spectre of repeat infections is well and truly upon us. Current vaccines were designed to protect against the original strain of SARS-CoV-2, and while the shots are crucial in shielding us from severe illness and death, they are less effective in preventing infection by newer variants.

 Unfortunately, natural immunity gained from a Delta infection also won’t stop us getting infected with Omicron. We learnt this with the rise of Omicron in South Africa late last year, when a population with relatively high natural immunity from previous coronavirus infections still fell victim to the merciless Omicron wave.

Reinfections have become something of a hallmark of Omicron. Since the rise of this highly transmissible strain, the number of people reinfected with coronavirus has spiked, in a pattern that is unique to the strain. Imperial College London researchers estimate a reinfection with Omicron is 5.4 times greater than with the Delta variant.

A letter published in The New England Journal of Medicine indicated that a previous COVID-19 infection was 90 per cent effective at preventing an infection with the Alpha, Beta or Delta variants, but only 56 per cent effective against Omicron.

In England, where Omicron has driven a spike in reinfections, provisional data from the UK Health Security Agency shows 10.7 per cent of all positive COVID-19 cases were reinfections in the last week of March.

The data shows that the number of weekly reinfections jumped from 20,000 to 50,000 in just one month, with reinfections occurring across all age groups, despite high vaccination levels. (A reinfection was counted when someone tested positive on two tests taken more than 90 days apart.)

Waning immunity is playing a part, along with the easing of restrictions. But the potent variable here is the rise of the BA.2 variant of Omicron, which is rapidly becoming the dominant strain globally.

A non-peer reviewed Swedish study suggests Omicron BA.2 could be more contagious than the original BA.1 strain due to its higher viral loads in the nose and throat. (The first case of a new recombinant variant combining BA.1 and BA.2, known as XE, was detected in New South Wales on April 9. Watch this space.)

The good news as far as reinfections go, is that catching the same variant twice is fairly unlikely. So if you got sick with Omicron BA.1, you’re probably in the clear when it comes to catching BA.2.

A more likely scenario is being reinfected after having Delta or an earlier strain. You’re more likely again to get infected if you’ve had no prior COVID infection at all, and that likelihood increases further if you’re unvaccinated.

While reinfection is no fun, the plus side is that it gives you excellent immunity when coupled with vaccination. The combination triggers a broader range of antibody and white cell responses in your system, meaning you are less likely to suffer serious illness on reinfection.

A preprint study from Qatar confirms that the best defence against Omicron BA.1 or BA.2 infections is a prior infection plus two vaccinations and a booster shot. This reduces the risk of infection by 77 per cent, compared with 52 per cent if you got three doses but had no prior infection, the study found.

Senior research fellow at the Kirby Institute’s infection analytics program Dr Deborah Cromer says COVID-19 may follow the trajectory of other respiratory viruses, such as the flu, when it comes to reinfection.

“People will get the flu once, but that doesn’t mean they won’t get the flu again,” she says. “They probably won’t get the flu twice in one season, but obviously, there are people who do. And if you’ve had the flu vaccine, it doesn’t mean you won’t get the flu, but your symptoms will probably be less severe.

“I think what we’re talking about is a respiratory virus that will keep changing, but if people’s immunity levels keep being maintained at a high level, then it should hopefully not be too severe.”

That’s pretty much how the 1918 Spanish flu petered out. The first couple of years of that pandemic were the worst in terms of severe sickness and death, but as the virus changed and spread over the following decades, it continued to infect people but was far less dangerous.

The key problem in Australia, though, is a lack of good data. As more people rely on rapid-antigen tests, there are fewer samples available for sequencing. ANU infectious diseases physician Peter Collignon says we need systematic surveillance to monitor infections and genomic sequencing to better understand how reinfections will impact us.

“Instead of having a one in 1000 chance of dying, is there one in 10,000 if you’re reinfected? What’s your chance of getting into hospital? And how is it proportionate to your socio-economic condition and your age? We need that sort of data to be able to plan for the future.”

Timna Jacks

By: Timna Jacks

Source: Why some people get COVID more than once

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