While COVID-19 has not disappeared, it no longer dominates daily life as it once did. However, the question of its resurgence and lasting health impacts remains. In our article series, you will find everything you need to know about the coronavirus pandemic.

As highlighted in a press release by ELTE, due to unprecedented international collaborations and monitoring efforts, a vast amount of data on the SARS-CoV-2 coronavirus has been compiled and is available online. This data aids continuous surveillance and forms the basis for numerous fundamental research studies.

With the involvement of researcher István Csabai's team, a European consortium has established the European Covid-19 Data Portal. The portal aims to analyze publicly available SARS-CoV-2 genome sequencing results using a standardized methodology. The database includes mutations within the genome of every sequenced sample and their prevalence rates among the virus population derived from individual patients.

This is important, the researchers emphasize, because the emergence of new mutations occurs often in low frequencies initially but can become more widespread if advantageous to the virus.

The prevalence rates (allele frequency values) can indicate whether multiple known variants such as Alpha, Delta, or Omicron are present in a sample. Co-infection with different variants might lead to more severe symptoms and the combination can potentially result in a third, so-called "recombinant" virus variant.

The data were analyzed by Orsolya Anna Pipek and Anna Medgyes-Horváth, marking the first time such a vast number of samples has been examined collectively in the world.

Summarizing the results published in the journal Nature Communications, 0.35 percent of the samples (a total of 7,700 cases) were found to contain characteristic patterns of at least two variants, with Delta and Omicron variants most commonly blending within a single sample.

Simultaneous infections require multiple variants to be circulating in society, as observed with Delta and Omicron between the end of 2021 and the beginning of 2022. Notably frequent coinfections occurred in South Africa, where the high number of HIV-related AIDS cases can, without proper treatment, result in immunodeficiency and prolonged infections. Such prolonged infections could have led to the emergence of the Omicron variant, which had significantly more mutations than previous variants and was more infectious.

Prolonged infections also increase the likelihood of co-infection, as patients have more time to contract another variant. Additionally, a weakened immune system might aid in the rapid reproduction of the virus, thus potentially giving rise to a hybrid genome.

Finally, the study aimed to examine whether recombination had occurred in samples with multiple present variants. Despite technical challenges, researchers using two newly developed methods successfully identified three regions in Delta-Omicron co-infections where recombination was frequent. The findings may contribute to the early detection of potentially dangerous hybrid viruses before they spread.