As it can be difficult to assess the neutralization activity just before infection in vaccinated patients, we assessed the neutralization activity and serum levels of the markers of the protective status or immune response during the acute phase, namely, type I and III interferons (IFNs), interleukin (IL)-6, C-X-C motif ligand (CXCL)-10, and vascular endothelial growth factor (VEGF), within 5 days after symptom onset in both vaccinated and unvaccinated patients admitted to the hospital. Here, IL6 is linked to infection.