From Delta to Omicron in 20 Days

Armelle Pérez-Cortés Villalobos, MD

May 13, 2022

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

A group of Spanish researchers presented an interesting case report last month at the 2022 European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Lisbon, Portugal: A 31-year-old woman who, just 20 days after testing positive for Delta, tested positive for Omicron. This is the shortest known gap between infections.

The woman was a healthcare worker who had a polymerase chain reaction (PCR) test done as part of routine staff screening at her place of work. On December 20, 2021, her results came back positive for SARS-CoV-2. She was asymptomatic at the time of the test and remained so during and after 10 days of isolation. In addition, she was fully vaccinated and had received a booster shot 12 days before testing positive.

On January 10, 2022, just 20 days after her first test came back positive, she presented with a cough, fever, and malaise. She had another PCR test done. As with the first, the results came back positive for SARS-CoV-2. Given the short interval between the two positive results, a decision was made to perform whole genome sequencing. This method confirmed that the patient had been infected by two different variants of SARS-CoV-2. The first, in December, was Delta; the second, in January, was Omicron. The latter is more infectious than Delta and remains the dominant strain worldwide.

One of the study's authors is Gemma Recio, MD, of the Catalan Health Institute in Tarragona, Spain. "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 reaffirming some important points, this report will be of great relevance to those seeking to better understand the disease. The first is that having COVID-19 doesn't preclude the possibility of being infected again. This also holds true for people with hybrid immunity, which was the case here: The patient was fully vaccinated and got COVID-19, and then, not long after, she got COVID-19 a second time. It's important to publicize her story so that people will know that if they've had COVID-19, they are not, in fact, protected against getting it again. Indeed, the degree of one's immune protection is something that is not known. And because new variants will inevitably emerge, everyone should consider taking the proper precautions.

Numerous factors could explain why this patient did not come down with a severe case or need to be hospitalized. In addition to her health status, she had already had COVID-19 and she was fully vaccinated.

Because of the slowdown in cases and the greater availability of rapid tests, significantly fewer PCR tests are being performed worldwide. Nonetheless, it's important that epidemiologic surveillance using sequencing be continued. Random sequencing will allow researchers to detect new variants and characterize those currently circulating to get a better understanding of their ability to partially evade the immune response.

Follow Armelle Pérez-Cortés Villalobos of Medscape Spanish Edition on Twitter @armelleID.

This article was translated from Medscape Spanish Edition.

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