Case study reports 20-day gap between two different COVID infections
Researchers in Spain are reporting on the case of a young healthcare worker testing positive to COVID-19 twice in 20 days. Genomic sequencing revealed the first infection was the Delta variant and the second was Omicron making this the shortest officially recorded gap between two SARS-CoV-2 infections.
The case study will be presented at this year’s upcoming European Congress of Clinical Microbiology & Infectious Diseases in Portugal and details a 31-year-old female healthcare worker who had her third COVID-19 vaccine dose 12 days before the first infection.
The first infection was detected through routine hospital COVID testing in December. The patient displayed no symptoms and genomic sequencing confirmed the infection was with the Delta variant of SARS-CoV-2.
After a 10-day isolation period the woman returned to work and came down with mild COVID-19 symptoms (cough and fever) on January the 10th, 2022. Another test again returned positive results and genomic sequencing this time found the infection to be due to the Omicron variant.
Gemma Recio, from Spain’s Institut Català de Salut, says her team’s findings are a potent reminder of the immune-evading ability of the Omicron variant.
“This case highlights the potential of the Omicron variant to evade the previous immunity acquired either from a natural infection with other variants or from vaccines,” said Recio. “In other words, people who have had COVID-19 cannot assume they are protected against reinfection, even if they have been fully vaccinated.”
The case is the shortest recorded gap between two COVID-19 infections officially reported to date. The big question yet to be answered is how common a phenomenon is this?
Since the emergence of the Omicron variant there have been increasing numbers of reinfections being reported. However, there is no general agreement over how to record COVID-19 reinfections.
The United Kingdom, for example, has been reporting on reinfection numbers for several months but is requiring a 90-day gap between two positive tests for a case to officially qualify as a reinfection. It has been argued that prolonged SARS-CoV-2 viral shedding can lead to frequent positive test results for weeks, or even months, after an acute infection. And without thorough genomic testing it is impossible to know for sure if a new wave of symptoms is a totally new infection and not just a reawakening of the first infection. So currently the UK is reporting about 10 to 15 percent of new cases as reinfections based on the 90-day rule.
The US Centers for Disease Control and Prevention (CDC) also works off the 90-day rule for classifying COVID-19 reinfections. The organization did publish a recent report chronicling 10 cases of COVID-19 reinfection that occurred less than 90 days apart.
All 10 cases in the CDC report were genetically confirmed as distinct reinfections and the average gap between infections was 54 days. The shortest reinfection gap in the CDC report was seen in an unvaccinated teenager for whom just 23 days separated a confirmed Delta infection and a confirmed Omicron infection.
It is impossible at this point to known just how prevalent COVID-19 reinfections are but Recio stressed the value of vaccination in protecting against severe COVID-19, despite the possible frequency of Omicron reinfection.
“This case also underscores the need to carry out genomic surveillance of viruses in infections in those who are fully vaccinated and in reinfections,” added Recio. “Such monitoring will help detect variants with the ability to partially evade the immune response.”
Lawrence Young, a virologist from the University of Warwick, said the new case study is a good example of the capacity for Omicron to reinfect individuals. The increasing rate of COVID-19 reinfections around the world is also a reminder that as long as SARS-CoV-2 continues to spread it will continue to mutate and new variants will arise.
“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,” said Young, who did not work on this new case study. “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.”