If you have recently contracted COVID-19 and thought that you were immune for a few months – you may have to think again. Researchers have found that the shortest-known COVID reinfection period is 20 days.
The findings were showcased in a presentation at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) in Lisbon, Portugal (23-26 April).
The unlucky person who contracted the virus was a 31-year-old healthcare worker. It is reported that the woman did not develop any symptoms after the first positive PCR test on December 20, 2021, and after a 10-day self-isolation period returned to work. However, she developed a cough and fever three weeks later and so took another test, and this too was positive.
Whole genome sequencing discovered that the woman was infected with two different variants – Delta in December and Omicron in January. The woman was fully vaccinated and had received a booster shot 12 days before her first positive test.
“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.” Dr Gemma Recio, one of the studies authors from the Institut Català de la Salut in Tarragona, said in a statement. "In other words, people who have had Covid-19 cannot assume they are protected against reinfection, even if they have been fully vaccinated.
"Nevertheless, both previous infection with other variants and vaccination do seem to partially protect against severe disease and hospitalisation in those with Omicron."
In the UK and US, it is no longer a requirement to take a confirmatory PCR test after a positive lateral flow test (LFD). Therefore, it is very difficult to determine the exact number of reinfection cases, as this requires whole genome sequencing to differentiate between different strains.
Currently, the virus is still classed as a pandemic – the World Health Organization (WHO) defines diseases as this when it has spread worldwide, and is unpredictably increasing in numbers. However, this disease is slowly heading towards becoming an endemic – which is similar to the common cold or flu, where case numbers are still large but at a more predictable rate. If coronavirus becomes a seasonal virus, scientists foresee that everyone will eventually catch COVID-19 twice, and probably many more times over the course of their lifetimes.
Despite this, COVID-19 variant monitoring is still very important even in people who are fully vaccinated, as this research will help pinpoint variants that can evade vaccines and the full effects of long COVID are still not known.