In a recent publication in Nature Communication the incidence and protective factors of SARS-CoV-2 omicron infection in triple vaccinated healthcare workers were investigated.

Vaccination is known to protect against severe COVID-19 but not effectively against infection. This study followed 368 triple vaccinated healthcare workers during four weeks with qPCR screenings twice weekly and serum antibody titer, viral abundance and clearance of infection determined at start of the study and upon omicron infection. During this period 22% of the participants had a breakthrough omicron infection independent on COVID-19 status of their patients or if they only were engaged in non-patient related work. By repeatedly measuring Spike-specific IgG levels, neutralization titers and mucosal spike-specific IgA-levels for those infected with omicron it could be shown that high levels of vaccine-induced spike-specific WT antibodies increase protection against infection and reduce viral load if infected. It is also suggested that the additive protective effect associated with pre-omicron infection is mainly dependent on mucosal spike-specific IgA and not by serum-IgG. The study involved research groups from both KTH (Royal Institute of Technology) and Science for Life Laboratory (SciLifeLab), Stockholm, Sweden.

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