"Both these variants were circulating in Belgium at the time, so it is likely that the lady was co-infected with different viruses from two different people. Unfortunately, we do not know how she became infected," Vankeerberghen added.

The team reported that the woman, whose medical history was unremarkable, was admitted to the hospital on 3 March, 2021, after a spate of falls.

She tested positive for Covid on the same day. She lived alone and received nursing care at home, and had not been vaccinated against Covid-19.

Further tests for VOCs with PCR confirmed the presence of two different strains of the virus–Alpha (B117), which originated in the UK, and Beta (B1351), first detected in South Africa.

Initially, there were no signs of respiratory distress and the patient had good oxygen saturation. However, she developed rapidly worsening respiratory symptoms, and died five days later.

In January 2021, scientists in Brazil reported that two people had been simultaneously infected with two different strains of the coronavirus–the Brazilian variant known as B1128 (E484K) and a novel variant VUI-NP13L, which had previously been discovered in Rio Grande do Sul. But the study has yet to be published in a scientific journal. Previous research has reported people infected with different influenza strains.

"Whether the co-infection of the two variants of concern played a role in the fast deterioration of the patient is difficult to say," Vankeerberghen said.

"Up to now, there have been no other published cases. However, the global occurrence of this phenomenon is probably underestimated due to limited testing for variants of concern and the lack of a simple way to identify co-infections with whole genome sequencing," she noted.

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