Abstract

Background: Insufficient evidence exists for comparing different COVID-19 vaccination schemes with CoronaVac in the adult and older adult populations. Methods: A prospective multicenter study was carried out with patients admitted for hospitalization due to COVID-19. Results: A study of 159 COVID-19 patients found that unvaccinated younger patients had a higher risk of oxygen requirement (RR = 1.3, p = 0.041) and dyspnea(p = 0.002). Critical care hospitalizations and the requirement of Invasive Mechanical Ventilation were less frequent across CoronaVac vaccines than in unvaccinated individuals. CanSino and BNT162b2-vaccines patients presented lower levels of D dimer than those vaccinated with CoronaVac. However, vaccinated individuals younger than 60 years old did not have a different risk of death than unvaccinated when presenting severe COVID-19, indicating insufficient vaccine-induced immunity. Conclusions: CoronaVac has a better response in older adults than in young people, and vaccination status did not significantly differ in young individuals with severe illness. Future studies should examine the effects of different vaccines on different age groups and their long-term follow-up, which can help countries make informed decisions for older adults' vaccination against COVID-19.