key: cord-0724441-pt1jxf7n
authors: Zeng, Guangting
title: Re: ' Vaccine Effectiveness of ChAdOx1 nCoV-19 Against COVID-19 in a Socially Vulnerable Community in Rio de Janeiro, Brazil' by Ranzani et al.
date: 2022-03-16
journal: Clin Microbiol Infect
DOI: 10.1016/j.cmi.2022.03.008
sha: 4bc40e07ff4dfb5ea5797fabd74fdfd89de643c9
doc_id: 724441
cord_uid: pt1jxf7n

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Community in Rio de Janeiro, Brazil' by Ranzani 

To the Editor:

Ranzani and colleagues evaluated the effectiveness of ChAdOx1 NCOV-19 against COVID-19 in a socially vulnerable community, and observed vaccine effectiveness increased up to 53.2% during 42-55 days of the first dose, and decreased afterwards in those that did not take the second dose 1 . They hypothesized that this decrease might occur in part because of an increase on the Delta dominance and wanin. I think it is more likely that the vaccine's immune protection declines over time, and the time-dependent decline is greater than the mutation-related decline 2 . Unfortunately, the study did not provide detailed estimates of changes in vaccine effectiveness over time.

In addition, there are several concerns about the study that could interfere with the results. First, age stratification using a median age of 35, rather than children, adults, and older adults, does not provide a good assessment of vaccine effectiveness in various populations. Studies have shown that the vaccine is less protective in older people and needs to be prioritized for booster shots 3 . Second, the study included periods dominated by Gamma and Delta and did not analyze them separately according to the onset of Delta. The infectivity, immune escape ability and pathogenicity of different mutants are different, which may cause confusion in the evaluation of vaccine effectiveness. Third, this analysis fails to account for potentially important confounding factors, including previous COVID-19 infection, populations with more sustained immune protection and possibly greater emphasis on personal protection 4 , such as wearing masks, that can influence the assessment of vaccine effectiveness. Fourth, the novel coronavirus vaccine may have cross-protection against other pathogens, leading to the conclusion that the vaccine protection effect is low. A study has found that being vaccinated against COVID-19 may help people fight off illnesses such as colds by inhibiting other coronaviruses 5 .

Vaccine effectiveness of ChAdOx1 nCoV-19 against COVID-19 in a socially vulnerable community in Rio de Janeiro, Brazil: a test-negative design study

Association of COVID-19 Vaccination With Symptomatic SARS-CoV-2 Infection by Time Since Vaccination and Delta Variant Predominance

Vaccine effectiveness of heterologous CoronaVac plus BNT162b2 in Brazil

Antibody responses and correlates of protection in the general population after two doses of the ChAdOx1 or BNT162b2 vaccines

SARS-CoV-2 Vaccination boosts Neutralizing Activity against Seasonal Human Coronaviruses

The author declares no competing interests.