Considerations in Boosting COVID Vaccine Immune Responses

As a new wave of COVID cases caused by the highly transmissible delta variant is exacerbating the worldwide public health crisis, this new wave has led to consideration of the potential need for and, optimal timing of booster doses for previously vaccinated recipients While the idea of further reducing the number of COVID cases by enhancing immunity in those previously vaccinated is appealing, any decision to do so should be evidence-based in the context of benefits and risks for individuals and society. Boosting might ultimately be needed in the general population because of waning immunity to the primary vaccination (defined as the original one‐ or two‐dose series of each vaccine) or because variants have evolved to the point where immune responses to the original vaccine antigens no longer adequately protect against circulating viruses. Boosting may also be justified for certain individuals in whom the primary vaccination series likely did not induce adequate protection, as may occur in the immunocompromised or in recipients of vaccines with low efficacy. Where primary vaccination did not induce adequate protection, an additional dose of the same vaccine may be helpful, or it may be appropriate to provide an additional dose of a different vaccine that may boost and complement the primary immune response.