It is unclear whether the
ChAdOx1 nCov-19 vaccine can induce the development of anti-PF4
antibodies in vaccinated individuals who have not developed
thrombosis. The aim of this prospective study was to evaluate the presence of
antibodies against
heparin/PF4 in adults who received a first dose of the
ChAdOx1 nCov-19 vaccine, and correlate them with clinical data and antibody responses to the
vaccine. We detected non-platelet activating anti-PF4
antibodies in 67% (29/43) of the vaccinated individuals on day 22 following the first dose of the
ChAdOx1 nCov-19 vaccine, though these were detected in low titers. Furthermore, there was no correlation between the presence of anti-PF4
IgG antibodies and the baseline clinical characteristics of the patients. Our findings suggest that the
ChAdOx1 nCov-19 vaccine can elicit anti-PF4 antibody production even in recipients without a clinical manifestation of
thrombosis. The presence of anti-PF4
antibodies was not sufficient to provoke clinically evident
thrombosis. Our results offer an important insight into the ongoing investigations regarding the underlying multifactorial pathophysiology of thrombotic events induced by the
ChAdOx1 nCov-19 vaccine.