HOW worried should we be about reinfections with Covid?

It is a question worth asking because repeat infections are becoming increasingly common and evidence suggests that even triple-vaccinated people who were exposed to the original strain of Omicron back in December or January may have little immune protection against infection by some of the sub-lineages now in circulation.

The rise of the Omicron variant has shattered any remaining illusions of herd immunity.

We are on the brink of our third Omicron wave in barely six months, with this one looking set to be driven by some combination of BA.4/5 and BA.2.12.1, having already passed through January’s BA.1 wave and the record-breaking BA.2 spike in March when, at one point, one in 11 Scots were infected.

HeraldScotland:

According to data from Public Health Scotland, in the two months from April 18 until June 19 a total of 13,009 cases reported in Scotland counted as suspected reinfections (where a person tests positive 90 days or more after their last positive test).

That is equivalent to 13.5 per cent of all known cases during that period, although the end of routinely available PCR testing from May 1 and a reliance on people self-reporting their own positive lateral flow results means many thousands more will have gone unreported.

From the outset, Omicron set itself apart from previous variants as a master of immune evasion, thanks mainly to the 37 mutations on its spike protein which make it difficult for antibodies to bind on.

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This means Omicron finds it much easier to latch onto human cells and slip inside, where it unleashes the process of viral replication which results in its human hosts feeling decidedly disinclined to boogie.

Its latest iterations - BA.4, BA.5 and BA2.12.1- have upped the stakes.

All three share mutations on an area of the spike protein known as L452 which scientists believe have evolved in direct response to the high levels of immunity generated by the huge Omicron waves.

Separate studies carried out at the Africa Health Research Institute in Durban, South Africa, and Peking University in China, found that antibody-rich blood from patients who had been infected with BA.1- the original form of Omicron - had only weak ability to neutralise BA.4 and BA.5; the same was true for BA.2.12.1.

HeraldScotland: Since emerging in southern Africa at the end of 2021, Omicron has given rise to successive new Covid waves caused by increasingly transmissible new sublineagesSince emerging in southern Africa at the end of 2021, Omicron has given rise to successive new Covid waves caused by increasingly transmissible new sublineages

This finding is echoed in a paper from Imperial College London published on June 14 which found that UK healthcare workers who had been triple-vaccinated but never infected and then caught Omicron actually mounted a stronger immune defence against previous Covid variants such as Delta and Alpha than they did against Omicron, leaving them exposed to repeat infections as new forms spring up.

Danny Altmann, a professor of immunology at Imperial, described Omicron as an “especially stealthy immune evader”, adding: “Not only can it break through vaccine defences, it looks to leave very few of the hallmarks we’d expect on the immune system – it’s more stealthy than previous variants and flies under the radar, so the immune system is unable to remember it.”

These findings are already calling into question the utility of Omicron-specific vaccines currently in development.

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That isn’t the only worry, however.

In May, Dr Kristian Andersen, a Californian-based expert in viral evolution, told Science magazine it was “certain” that the Omicron family tree “will continue to be more and more capable of immune escape”.

In time, he said, that might mean reduced protection not just against infection, but also against severe disease.

Setting aside that ominous possibility, however, is there anything inherently dangerous for the individual about reinfection compared to, well, infection?

This issue caught fire on social media this week with the publication of an American preprint study (not-yet peer-reviewed, or published in a journal) led by a team at Washington University School of Medicine in St Louis.

 

 

The study, posted online on July 17, is among the first to specifically evaluate the health consequences of reinfection, but has been widely misinterpreted as demonstrating that the risk of hospitalisation, death, and Long Covid increases exponentially with each new infection.

What it actually shows is that reinfection with Covid adds to the overall risk of death, hospitalisation and some health conditions compared to not being reinfected at all.

This might seem fairly obvious, but it is important because it underlines the fact that reinfection is not necessarily benign.

As the authors put it: "In this study of 5,693,208 we provide evidence that reinfection contributes additional health risks beyond those incurred in the first infection including all-cause mortality, hospitalisation, and sequelae [conditions resulting from previous disease] in the pulmonary and broad array of extra-pulmonary organ systems.”

In other words, each repeat infection adds to overall risk of dying from any cause, needing hospital care, or suffering long term lung and organ damage.

This does not mean that a second or third infection is more acute; only that repeat infections come with a cumulative risk of harm which is “not trivial”.

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It is worth noting, however, that the 5.6m medical records studied came from a healthcare database of US veterans whose primary infections (and some reinfections) all occurred between March 2020 and September 2021, predating Omicron.

Although follow-up continued until early April 2022, it is unclear how relevant the results are for Omicron, which is less virulent than Delta.

Participants were also 90% male; more than half were current or former smokers; and the average age was nearly 63.

Nearly 90% were unvaccinated at the time of their reinfection, and 20% had been hospitalised at the time of their first infection.

The results may not be representative for the population at large, therefore.

Nonetheless, repeat waves of Covid are bad news for the NHS.

It means more staff absences, fewer beds, more planned operations cancelled, and more bottlenecks in A&E.

And that, undoubtedly, is a problem for all of us.