Re: “Postinfectious Immunity After COVID-19 and Vaccination Against SARS-CoV-2” by Krsak et al.

To the Editor:

We would like to share ideas on the publication “Postinfectious Immunity After COVID-19 and Vaccination Against SARS-CoV-2 (3).” Krsak et al. concluded that “anyone who is within the CDC-specified period of ….. (3)” and “Such single-dose boosting could,….. health care workers and first responders (3).” We agree that vaccination for a person previously infected with COVID-19 might not be necessary. Apart from the immunological issue that Krsak et al. mentioned, there are other important considerations. There are lines of evidence that support and do not support vaccination for a person infected previously with COVID-19. First, there are many new emerging SARS CoV-2 variants at present. Whether immunity due to previous COVID-19 infection can cross protect new SARS CoV-2 variants is an interesting question. Regarding the present available vaccine, the efficacy against SARS CoV-2 variants is still questionable (1). Moreover, we should consider the possible risk of unnecessary vaccination to a person with previous COVID-19 infection. The previous COVID-19 infection can result in increased blood viscosity and vaccination might further cause a hyperviscosity problem, adverse effect of vaccine (2).