Long-lasting T-cell response to SARS-CoV-2 antigens after vaccination-a prospective cohort study of HCWs working with COVID-19 patients.

BACKGROUND: Vaccination against SARS-CoV-2 reduces the risk of hospitalisation and death, but vaccine-induced IgG antibodies against the spike protein (IgG S) decline over time. Less is known about the nature of the vaccine-induced T-cell response to SARS-CoV-2 antigens. METHODS: IgG antibodies against nucleocapsid protein (IgG N), IgG S, and T-cell response towards SARS-CoV-2 antigens were determined in samples taken between November 2020 and November 2021 from a cohort of healthcare workers at an Infectious Diseases Department. RT-PCR screening for SARS-CoV-2 was encouraged once every four weeks in addition to testing when symptomatic or identified through contact tracing. Vaccination data were collected at the end of the study. RESULTS: At inclusion, T-cell response to SARS-CoV-2 antigens was found in 10/15 (66.7%) of participants with a previous/current COVID-19 infection and in 9/54 (16.7%) of participants with no prior/current history of COVID-19 infection. All participants with complete follow-up (n = 59) received two doses of a SARS-CoV-2 vaccine during the study. All participants demonstrated detectable IgG (S) antibodies at the end of the study, in median 278 days (IQR 112) after the second vaccine dose. All but four participants displayed T-cell responses towards SARS-CoV-2 antigens. IgG S antibody levels correlated with time since the second vaccine dose. In addition, previous COVID-19 infection and the strength of the S1 T-cell response correlated with IgG S antibody levels. However, no correlation was demonstrated between the strength of the T-cell response and time since the second vaccine dose. CONCLUSION: COVID-19 vaccination induces robust T-cell responses that remain for at least nine months.