Serological assessment is advisable before COVID-19 vaccination.

Dear Editor,

We read with interest the article of Joshi et al., who reported that previously infected healthcare workers receiving coronavirus disease 2019 (COVID-19) vaccination experimented a higher incidence of adverse events following immunization (AEFI). This important finding provides substantial support to the previous evidence that vaccine reactogenicity, along with the consequent risk of developing local or systemic reactions, is magnified in subjects who recovered from a previous severe acute respiratory disease coronavirus 2 (SARS-CoV-2) infection, either symptomatic or asymptomatic.

The rate of asymptomatic SARS-CoV-2 infections varies widely according to population characteristics but has been reported to be as high as 80% in certain studies. This vast number of subjects with a previous asymptomatic SARS-CoV-2 infection should be accurately identified before undergoing COVID-19 vaccination for at least two clinical and epidemiological motivations. The first reason is for preventing the high risk of developing AEFI in these subjects, as clearly evidenced by Joshi et al. in their study. The second important aspect is that we and others have shown that the humoral response developing after COVID-19 vaccination is orders of magnitude higher in healthcare workers with previous SARS-CoV-2 infection than in those without,, such that a dose reduction (i.e., lowering the dosage of single-administration vaccines or averting the booster in two-dose vaccines recipients) may be advisable. This will contribute to optimize vaccine usage and reduce their worldwide shortage, especially in more vulnerable countries, including India.

The measurement of anti-SARS-CoV-2 neutralizing antibodies via fully automated, fast, high-throughput, and relatively inexpensive immunoassays is now possible and should thus be widely encouraged before COVID-19 vaccination. Their post-vaccine assessment may also help to solve the dilemma raised by Bobdey et al. on the optimal dose interval of COVID-19 vaccine administration since the period from the first vaccine dose to the booster could be specifically tailored according to the serum levels of anti-SARS-CoV-2 neutralizing antibodies, while consideration of administering a third dose could be made in older and/or immunocompromised subjects, who often display insufficient serologic response to the administration of the first two doses.

Conflicts of interest

The authors have none to declare.