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expert reaction to poster looking at a case study of a woman who tested positive for the omicron variant 20 days after being infected with the delta variant

A poster presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) Annual Meeting looks at a case report of omicron infection just 20 days after delta.


Prof Paul Hunter, Professor in Medicine, UEA, said:

“This case is not particularly surprising, though the gap between infections is particularly short . We have known for some months that reinfections will occur. The omicron variant with its escape mutations has made reinfections even more likely.

“Even before omicron, Townsend and colleagues suggested that “Reinfection by SARS-CoV-2 under endemic conditions would likely occur between 3 months and 5·1 years after peak antibody response, with a median of 16 months”.  So the omicron variant will have reduced the period.

“But a prior delta infection during the summer or autumn of last year still provides substantial protection against infection, about 50%  which is actually much better than protection from a booster dose of vaccine (see figure 1)

“It is likely that a prior omicron will provide even better protection against further omicron infections than a prior delta infection, but it is too early to be able to estimate how much better. But even if we do not get anymore variants (unlikely) we will still get reinfections from omicron as immunity wanes.

“We can expect further waves of infection especially during winter even without new variants. Fortunately the evidence is that immunity to severe disease is more robust than immunity to infection. So even though reinfections will continue to occur for many years, we will see fewer and fewer severe illness and deaths with time.”


Prof Lawrence Young, Virologist and Professor of Molecular Oncology, University of Warwick, said:

“The ability of previously infected individuals to get re-infected, particularly with a different variant, is well-documented. This case shows that previous vaccination was not sufficient to protect this healthcare worker from infection with the delta variant although it was very likely to have prevented the development of symptoms. Infection 20 days later with the omicron variant resulted in symptomatic disease. While it’s difficult to extrapolate from a single case, this report highlights the ability of the omicron variant (and its sub-variants) to re-infect even in those individuals who are fully vaccinated. This is a product of the increased infectiousness of the omicron variant and its associated ability to evade the protective immunity induced by previous infection and/or vaccination. This accounts for the extremely high levels of infection we have experienced in the UK. This case also emphasises the need to maintain surveillance systems to detect new variants. It reinforces the fact that as long as the virus continues to spread and replicate, it will throw up new variants and these will remain a continual threat even to those countries with high rates of vaccination. It is wrong to assume that any new variant will be less infectious and less dangerous than previous variants particularly as immunity induced by infection and vaccination wanes over time and current vaccines may not be as protective against these new variants.”



The press release is based on ePoster L0438 at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) Annual Meeting. The material has been peer reviewed by the congress selection committee. There is no full paper at this stage and the authors have not yet submitted the work to a medical journal for a publication.



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Declared interests

None received.


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