The Pfizer and Astra-Zeneca COVID-19 vaccines require that you get the two shots for the best immune response. It is stated that you will start to have partial protection within 12 days after the first shot. This partial protection is thought to be short-lived. The second shot encourages the body to build stronger immunity against COVID-19. A person may not have the full protection of the second shot for 7-14 days after it is received. Since this is the case, you can still become ill shortly after getting the second shot. It is best to continue safe practices after you have received your shots.