Adenoviral COVID-19 vaccines, like AstraZeneca, ChAdOx1, and J&J Ad26.COV2.S, can provoke Th1and CD8 T cell responses, while inactivated virus COVID-19 vaccines, such as CoronaVac and Covaxin (BBV152), induce comparatively modest CD4 T cell responses and a combination of Th1 and Th2 cells as well as a weak CD8 response. Here, CD4 is linked to COVID-19.