There is virtually no protection against infection with the currently circulating omicron variant of the SARS-CoV-2 virus for dual-vaccinated and recovered individuals who were infected with the previous SARS-CoV-2 variants.
In a new study from MedUni Vienna, researchers found only people who have been immunized against COVID-19 with a third vaccination form antibodies that can partially block omicron.
They examined vaccinated and recovered people to see their antibody status and protection against the virus that originated in Wuhan as well as the delta and omicron variants.
For this purpose, a test developed for the previous variants, which investigates whether the virus can bind to the receptor on human cells via its receptor-binding domain (RBD), was rapidly adapted for omicron, which, if needed, can also be done for any newly emerging variant swiftly.
The team found that both COVID-19 convalescent individuals and individuals who had been vaccinated twice had developed antibody protection against delta.
However, the antibodies were not able to block receptor binding against omicron.
Blockade of omicron was better in those individuals who had received the third vaccination.
However, there is also a significant proportion (20%) that was not protected by vaccination.
The receptor-binding domain (RBD) which is used by SARS-CoV-2 to enter human cells via the ACE2 receptor differed only slightly in all previously known SARS-CoV-2 variants so that infections with these and the currently available vaccines provided protection against the previous coronavirus variants.
Omicron is the first variant that differs greatly from the previous variants in RBD, consequently, infections with the previous variants and currently available vaccines provide little or no protection against omicron.
The team says for the immunologist, the best protection under such circumstances would be to develop a broadly effective combination vaccine that protects against both the previous variants and omicron.
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The study is published in Allergy and was conducted by Rudolf Valenta et al.
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