* require hfnc, non-invasive ventilation, invasive mechanical ventilation, or ecmo on day 1 at the time of randomization. * have history of or current thrombosis. only if current thrombosis is suspected, imaging testing is recommended (e.g. ctpa or per local guidance) to exclude thrombosis. * have a personal or first degree family history of blood clotting disorders. * participants who are immunocompromised, with known immunodeficiencies, or taking potent immunosuppressive agents (e.g. azathioprine, cyclosporine). * participants with any current malignancy or lymphoproliferative disorders that requires active treatment. * suspected or known active systemic bacterial, fungal, or viral infections (with the exception of covid-19). * severe hepatic impairment, defined as child-pugh class c. * severe anemia (hemoglobin \< 8 g/dl) * any of the following abnormalities in clinical lab tests at screening, confirmed by a single repeat, if deemed necessary: alc \< 500 cells/mm3, anc \< 1000 cells/mm3 * known allergy to tofacitinib

* require hfnc, non-invasive ventilation, invasive mechanical ventilation, or ecmo on day 1 at the time of randomization. * have history of or current thrombosis. only if current thrombosis is suspected, imaging testing is recommended (e.g. ctpa or per local guidance) to exclude thrombosis. * have a personal or first degree family history of blood clotting disorders. * participants who are immunocompromised, with known immunodeficiencies, or taking potent immunosuppressive agents (e.g. azathioprine, cyclosporine). * participants with any current malignancy or lymphoproliferative disorders that requires active treatment. * suspected or known active systemic bacterial, fungal, or viral infections (with the exception of covid-19). * severe hepatic impairment, defined as child-pugh class c. * severe anemia (hemoglobin \< 8 g/dl) * any of the following abnormalities in clinical lab tests at screening, confirmed by a single repeat, if deemed necessary: alc \< 500 cells/mm3, anc \< 1000 cells/mm3 * known allergy to tofacitinib

- require hfnc, non-invasive ventilation, invasive mechanical ventilation, or ecmo on day 1 at the time of randomization. - have history of or current thrombosis. only if current thrombosis is suspected, imaging testing is recommended (e.g. ctpa or per local guidance) to exclude thrombosis. - have a personal or first degree family history of blood clotting disorders. - participants who are immunocompromised, with known immunodeficiencies, or taking potent immunosuppressive agents (e.g. azathioprine, cyclosporine). - participants with any current malignancy or lymphoproliferative disorders that requires active treatment. - suspected or known active systemic bacterial, fungal, or viral infections (with the exception of covid-19). - severe hepatic impairment, defined as child-pugh class c. - severe anemia (hemoglobin < 8 g/dl) - any of the following abnormalities in clinical lab tests at screening, confirmed by a single repeat, if deemed necessary: alc < 500 cells/mm3, anc < 1000 cells/mm3 - known allergy to tofacitinib

- require hfnc, non-invasive ventilation, invasive mechanical ventilation, or ecmo on day 1 at the time of randomization. - have history of or current thrombosis. only if current thrombosis is suspected, imaging testing is recommended (e.g. ctpa or per local guidance) to exclude thrombosis. - have a personal or first degree family history of blood clotting disorders. - participants who are immunocompromised, with known immunodeficiencies, or taking potent immunosuppressive agents (e.g. azathioprine, cyclosporine). - participants with any current malignancy or lymphoproliferative disorders that requires active treatment. - suspected or known active systemic bacterial, fungal, or viral infections (with the exception of covid-19). - severe hepatic impairment, defined as child-pugh class c. - severe anemia (hemoglobin < 8 g/dl) - any of the following abnormalities in clinical lab tests at screening, confirmed by a single repeat, if deemed necessary: alc < 500 cells/mm3, anc < 1000 cells/mm3 - known allergy to tofacitinib