Data coming out of Israel,
, showed Pfizer vaccine is not very effective against the South Africa strain. Of 400 infected cases that got the Pfizer shot(s), the prevalence of the SA strain is 5.4% while infected cases without any vaccine showed SA strain prevalence of 0.7%. The Pfizer vaccine is effective against the main strain. If I did the calculation right, assuming Pfizer is near 92 effective against the main strain in Israel, it is only 30-40% effective against the SA strain and so naturally you need 3rd shot, and annual shots if the virus continues to mutate.