It is common for vaccine-induced immunity to wane over time for some vaccines.
The current WHO-approved vaccines provide substantial protection for at least six months against severe disease, hospitalization and death from COVID-19. This waning has resulted in reduced effectiveness against mild and asymptomatic infection with Omicron and Delta variants, and the need for a booster dose to restore a sufficient level of protection.
WHO has recommended that a booster dose should be offered 4-6 months after completion of the primary series to maintain the high level of protection against severe disease. Furthermore, for people with impaired immune system, an additional dose in the primary series is recommended to mount a proper immune response.
It is important to take all vaccine doses you are offered to maintain the highest level of protection. Consult your health practitioner for the recommended number of doses.
More research is needed to continue evaluating vaccine effectiveness beyond six months, and following administration of a booster dose.