Similar viral loads in Omicron infections regardless of vaccination status

Background Although SARS-CoV-2 booster vaccinations are underway, breakthrough infections with Omicron variants are occurring. This study analyzed associations between Omicron sublineage (BA.1.1 and BA.2) viral load and vaccination history. Methods Viral loads in nasopharyngeal swabs were evaluated by quantitative real-time PCR, and the virus strain was evaluated by whole-genome analysis or TaqMan assay. Results A total of 611 patients positive for an Omicron SARS-CoV-2 variant were included; 199 were unvaccinated, 370 had received two vaccine doses, and 42 had received three doses. Similar viral loads and Ct values of BA.1.1 and BA.2 were detected regardless of vaccination history. No correlations between age and BA.1.1 and BA.2 viral load were observed. Conclusion Omicron-infected patients who had received a third vaccine dose had viral loads similar to patients with two doses or who were unvaccinated.