Letter to editor about the articles of "Six-month sequelae of post-vaccination SARS-CoV-2 infection: A retrospective cohort study of 10,024 breakthrough infections".

Dear editor:

With great interest, we read the article of “Six-month sequelae of post-vaccination SARS-CoV-2 infection: A retrospective cohort study of 10,024 breakthrough infections” by Taquet et al. (Taquet et al., 2022). The authors reported COVID-19 vaccination (at least one dose) was associated with lower risk of several COVID-19 sequalae in those with breakthrough SARS-CoV-2 infection. We appreciate the population-based cohort study with empathizing the necessity of vaccination and outcomes evaluation. Nevertheless, there were some research designs we would like to discuss.

First, the unvaccinated matched group were included by whom had received an influenza vaccine at “some point” of their electronic health records network. The inclusion criteria meant to exclude individuals with vaccine hesitancy as health-related behaviors that might confound associations with COVID-19 outcomes. “Some point” may be years ago and this could not represent their health-related behaviors during pandemic in the study. Besides, if they received influenza vaccine in previous one or two years, it might be more possible they also received COVID-19 vaccine (without records in this network for some reasons). Because outright vaccine refusal of COVID-19 seemed to be corelated to poorer compliance of recommended influenza vaccine in the past (Michael et al., 2021). The inclusion criteria were ambiguous and cannot eliminate the possible confounding effect.

Second, the primary cohort contained patients received partial (one dose) or fully (two doses) COVID-19 vaccination. The outcomes (acute or post-acute sequalae) should be interpreted very carefully, since the effectiveness and breakthrough infection are dose-dependent (Haas et al., 2021). It could also interfere the conclusion that protective effects were smaller and not robust in those60-year-old. Either the matched cohort comprised some individuals with COVID-19 vaccinated, or the outcomes were evaluated regardless of one or two doses lead to attenuate the protective effects of vaccine in those60-year-old in the study (Meseret et al., 2021, COVID Data Tracker 2022 COVID Data Tracker 2022, 2022). Since public health policy advise fully vaccination, high risk group such as elderly should be analyzed with different doses, separately.

Above all, the study provided essential information about sequalae of breakthrough infections. However, some bias need to be considered.

Funding statement

No specific funding was received from any bodies in the public, commercial, or not for profit sectors to carry out the work described in this article.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.