inclusion criteria: * adult aged at least 18 years * previously vaccinated with 2 (or more) doses of any licensed covid-19 vaccine who requires initiation of moderate-to-severe immunosuppression; most recent covid-19 vaccine dose must have been given \> 3 months prior * planned significant immunosuppressive therapy for at least 1 year * no cyclophosphamide, alemtuzumab or rituximab treatment in the past 5 years. note: patient may have concurrent steroids with any treatments listed in protocol * voluntarily given written informed consent

inclusion criteria: * adult aged at least 18 years * previously vaccinated with 2 (or more) doses of any licensed covid-19 vaccine who requires initiation of moderate-to-severe immunosuppression; most recent covid-19 vaccine dose must have been given \> 3 months prior * planned significant immunosuppressive therapy for at least 1 year * no cyclophosphamide, alemtuzumab or rituximab treatment in the past 5 years. note: patient may have concurrent steroids with any treatments listed in protocol * voluntarily given written informed consent

inclusion criteria: * adult aged at least 18 years * previously vaccinated with 3 (or more) doses of any licensed covid-19 vaccine who requires initiation of moderate-to-severe immunosuppression; third covid-19 vaccine dose must have been given \> 3 months prior * planned significant immunosuppressive therapy for at least 1 year * no significant immunosuppression in the past 5 years. * evidence of prior tetanus toxoid vaccination (detectable tetanus toxoid igg at screening) * voluntarily given written informed consent

inclusion criteria: * adult aged at least 18 years * previously vaccinated with 3 (or more) doses of any licensed covid-19 vaccine who requires initiation of moderate-to-severe immunosuppression; third covid-19 vaccine dose must have been given \> 3 months prior * planned significant immunosuppressive therapy for at least 1 year * no significant immunosuppression in the past 5 years. * evidence of prior tetanus toxoid vaccination (detectable tetanus toxoid igg at screening) * voluntarily given written informed consent

inclusion criteria: adult aged at least 18 years previously vaccinated with 3 (or more) doses of any licensed covid-19 vaccine who requires initiation of moderate-to-severe immunosuppression; third covid-19 vaccine dose must have been given > 3 months prior planned significant immunosuppressive therapy for at least 1 year no significant immunosuppression in the past 5 years. evidence of prior tetanus toxoid vaccination (detectable tetanus toxoid igg at screening) voluntarily given written informed consent

inclusion criteria: adult aged at least 18 years previously vaccinated with 3 (or more) doses of any licensed covid-19 vaccine who requires initiation of moderate-to-severe immunosuppression; third covid-19 vaccine dose must have been given > 3 months prior planned significant immunosuppressive therapy for at least 1 year no significant immunosuppression in the past 5 years. evidence of prior tetanus toxoid vaccination (detectable tetanus toxoid igg at screening) voluntarily given written informed consent