After exhausting years of the Covid pandemic with multiple waves of infections caused by ever-changing virus variants, and with corresponding hospitalisation rates, the situation has significantly improved. Large infection waves outside the cold and wet seasons are not occurring. This success is largely attributed to the rapid development of vaccines. Many people have been immunised against SARS-CoV-2. Booster vaccinations with adapted vaccines, known as booster shots, as well as infections in vaccinated individuals with currently circulating virus variants, have further trained our immune systems so that they can also counter newly emerging virus variants.
A part of our immune protection relies on neutralising antibodies produced by the cells of our immune system after vaccination or infection. These neutralising antibodies attach to the spike protein of SARS-CoV-2, preventing the virus from entering our cells. This mechanism is also referred to as neutralisation.
However, even with neutralising antibodies, 100% protection against SARS-CoV-2 infection is not guaranteed because SARS-CoV-2 can still change. This leads to the emergence of mutated virus variants that can gain the ability to partially evade neutralising antibodies. The process is also known as “antibody escape” and is based on mutations in the spike protein that make it less optimal for neutralising antibodies to bind to.
“Mutations can enhance the transmissibility of SARS-CoV-2 variants by, for example, improving the binding of the spike protein to the cellular receptor ACE2,” said Markus Hoffmann, the leading scientist behind the study, published in The Lancet Infectious Diseases.
Since May 2023, the SARS-CoV-2 lineage EG.5 (including its descendant EG.5.1), has been on the rise in many countries. The lineage, classified as a “Variant of Interest” by the World Health Organization (WHO), is also referred to as Eris, named after the Greek goddess of chaos and discord. While this name may sound dangerous, there is currently no evidence to suggest that infections with EG.5 and EG.5.1 are leading to more severe illnesses.
However, it is still unclear what is causing the increasing spread of EG.5 and EG.5.1. A team of scientists from the German Primate Center – Leibniz Institute for Primate Research in Göttingen, the Hannover Medical School, and Friedrich-Alexander University Erlangen-Nuremberg has investigated the Eris sublineage EG.5.1. “We have found evidence that an increased ability to escape from antibodies is the likely cause for the enhanced spread of Eris,” said Hoffmann.
Lu Zhang, the lead authors of the study, explained: “We tested how effectively the Eris sublineage EG.5.1 can enter host cells and how efficiently it is neutralised by antibodies in the blood of vaccinated individuals without a SARS-CoV-2 infection and those with a SARS-CoV-2 infection. During this process, we found that, in comparison to other currently circulating SARS-CoV-2 lineages, EG.5.1 does not possess an advantage in infecting host cell. However, further investigations revealed that EG.5.1 is less effectively neutralised by antibodies present in the blood of vaccinated individuals, or vaccinated and infected individuals.”
“In summary, our results suggest that the spread of EG.5 and its sublineages primarily relies on antibody escape rather than an enhanced ability to infect host cells. However, the increase in the ability to escape antibodies is rather moderate and by no means sufficient to completely undermine our immunity that has been established through vaccination or prior infection,” commented Hoffmann on the outcome of the study.
In the autumn of this year, newly adapted SARS-CoV-2/Covid vaccines based on the widespread XBB.1.5 lineage of SARS-CoV-2 will be deployed. Now the question arises: Will these vaccines also be effective against EG.5 and its sublineages?
“Since Eris is a descendant of the closely related XBB.1.9 lineage, and the various XBB sublineages exhibit only minor differences among themselves, it can be assumed that the newly adapted vaccines will also be effective against EG.5 and its sublineages. Primary and booster vaccination, especially for high-risk groups and their close contacts, are therefore advisable,” concluded Stefan Pöhlmann, Head of the Infection Biology Unit at the Leibniz Institute for Primate Research.
