Emerging evidence suggesting waning levels of immune markers with time, particularly against more virulent variants. How this will correlate to functional immunity is yet to be documented.
Immunocompromised populations with lower levels of responses to standard 2-dose regimens may benefit from a 3rd dose of mRNA vaccine as a part of the primary series, though their response may still be lower than what is expected in the general population
Current recommendation for populations to receive a 3rd dose include adults over a certain age (depending on jurisdiction), those living in long-term care settings, frontline health and social workers and/or people working in high risk settings, those with immune compromising conditions leading to increased risk of severe disease/poor outcomes if infected
Safety trials have indicated that side effects to 3rd/booster doses are similar to those following the 2nd dose in initial vaccination series
Badea, A; Groot, G; Muhajarine, N; Lee, S; Shumilak, G; Hernandez-Ronquillo, L; Tian, K. What is the current evidence and recommendations regarding COVID-19 vaccine booster shots (exceeding 2 doses) for the general population? 2021 Oct 07, Document no.: EOC210902 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2021. 8 p. (CEST rapid review report).