COVID-19: Omicron's stealthy behaviour behind reinfections in people with immunity, says new study

People infected with initial strains had less sustained antibody response to omicron, scientists find

By Taran Deol
Published: Wednesday 22 June 2022

The stealthy nature of the omicron strain of SARS-CoV-2 may be behind the large number of reinfection cases linked with the variant, according to a new study. 

The human immune system doesn’t remember encountering the fifth ‘variant of concern’ because it is so stealthy, it said. So when the virus enters the body again, it is unable to muster a response to prevent an infection, the scientists found.  

They also observed that patients who had contracted COVID-19 during earlier waves, triggered by the ‘Wuhan strain’ and the alpha variant, “showed a less sustained antibody response against omicron”.

The study published in Science journal on June 14, 2022 was conducted by experts from the United Kingdom Health Security Agency, Imperial College London, University College London and other leading institutes in the country. 

They assessed T- and B-cell immunity against omicron in 731 triple mRNA vaccinated healthcare workers (HCW) with different SARS-CoV-2 infection histories from March 2020-January 2022. 

The findings challenge the notion we have had till now that being infected with COVID-19 provides some amount of natural immunity, albeit for a short period of time, according to experts. Since the emergence of omicron, several anecdotal evidence of reinfections within weeks of first being infected have been reported.

The paper noted: 

Previously infection-naïve HCW who became infected during the omicron wave showed enhanced immunity against earlier variants, but reduced neutralising antibody potency and T-cell responses against omicron itself. 

This means those who have received three doses of the vaccine and got COVID-19 for the first time during the omicron wave did not develop an immune response to the variant even after the infection and were thus vulnerable to breakthrough infections. 

Danny Altmann, professor wLondon’s departmentith Imperial College of immunology and inflammation, said: “We have found that omicron is far from a benign natural booster of vaccine immunity, as we might have thought, but it is an especially stealthy immune evader. While the study looked at BA.1, experts believe its subvairants — BA.4 and BA.5 — will likely have a similar behaviour.

These findings come at a time when “there is a view that the global spread of omicron, through its association with a relatively milder disease phenotype and, possibly, a potential to boost vaccine immunity, may herald the transition into a new, endemic relationship,” the authors noted in the paper. 

The report also had an assessment of the kind of protection one gets from prior infection and a triple dose of the vaccine. Here, the researchers encountered a phenomenon they termed ‘immune imprinting’. 

This means the immune system remembers a pattern of immunity based on the number of vaccination doses received and the variant of COVID-19 a person is infected with. Since not everyone has received the same number of doses nor were they infected by the same variant, immune patterns differ. 

The findings on the relation between immune imprint and subsequent protection were not only “profound and negative” but also an “unexpected consequence” of the pandemic. “While it is known that cross-reactive antibody recognition is compromised by the mutations in omicron, it was surprising that this was so profoundly exacerbated by differential imprinting in those having had prior infection with either Wuhan Hu-1 or B.1.1.7 (Alpha),” the authors noted.

While protection against an infection wanes, vaccination continues to prevent severe disease and death when infected with SARS-CoV-2, they maintained. However, the impact of even a mild infection and reinfection on Long Covid remained unexplored, the scientists wrote. 

“A concern is that omicron could potentially mutate further into a more pathogenic strain or become better able to overcome vaccine protection,” Boyton said. 

In this scenario, people who have had omicron infection would be poorly boosted against future infection depending on their immune imprinting, he added.

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