**1. Introduction**

3

SARS-CoV-2 vaccines can reduce disease occurrence and transmission in a population. This is essential to reduce both morbidity and mortality from SARS-CoV-2 [1]. Consequently, there is a need for evidence on the effectiveness of vaccines to protect not only against SARS-CoV-2 symptoms but also to reduce COVID-19-related case fatality rates [2]. However, the reduction in the occurrence of severe disease and death is difficult to evaluate in phase 3 clinical trials, mainly due to the high number of participants required [1]. Thus, the effectiveness of SARS-CoV-2 vaccines in relation to case fatality has to be inferred from other sources of data, such as mortality statistics [3].

In Brazil, by the end of June 2021, more than 18.5 million cases and more than 500,000 deaths were confirmed, with a case fatality rate of 2.8% [4]. The state of Ceará, with a population of 8.8 million, was one of the first Brazilian states to confirm sustained transmission of COVID-19 in 2020 [5]. Despite the rapid implementation of control measures, Ceará stands out with more than 880,000 cases and almost 22,500 deaths by the end of June 2021 [4]. The case fatality rate was 2.5%, and there was a high rate of hospital bed occupancy (>90%), while different strains of SARS-CoV-2 were circulating [5].

A recent case-control study in England, including almost 160,000 adults aged over 70 years, evidenced a significant reduction in symptomatic COVID-19 cases and severe

**Citation:** Alencar, C.H.; Cavalcanti, L.P.G.; Almeida, M.M.; Barbosa, P.P.L.; Cavalcante, K.K.S.; Melo, D.N.; Alves, B.C.F.B.; Heukelbach, J. High Effectiveness of SARS-CoV-2 Vaccines in Reducing COVID-19-Related Deaths in over 75-Year-Olds, Ceará State, Brazil. *Trop. Med. Infect. Dis.* **2021**, *6*, 129. https://doi.org/ 10.3390/tropicalmed6030129

Academic Editor: John Frean

Received: 15 June 2021 Accepted: 10 July 2021 Published: 13 July 2021

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symptoms after a single dose of the Oxford-AstraZeneca vaccine [6]. A recent study with Brazilian data showed an association between the rapid increase in vaccination coverage of the older population and relative mortality, as compared to younger individuals, in a setting where the gamma variant was predominant, and the most widely used vaccine was CoronaVac-Sinovac/Butantan [7]. The Brazilian Ministry of Health has made available both vaccines from Oxford-AstraZeneca/Fiocruz and CoronaVac-Sinovac/Butantan. In Ceará, by May 2021, more than 1.7 million people had taken at least one dose of a vaccine, with more than 500 thousand people having received two doses [8]. In this study, we evaluated the hypothesis that COVID-19 vaccinations had a considerable impact on reducing the number of deaths due to COVID-19 in the state of Ceará, Northeast Brazil, in the year 2021.

#### **2. Materials and Methods**

People aged 75 years or older were included since this age group was prioritized by the Brazilian Immunization Program and, thus, had a higher proportion of vaccination coverage at the beginning of the campaign. For the year 2021, the estimated population in this age group was 354,269 people (IBGE—Brazilian Institute of Geography and Statistics/*Instituto Brasileiro de Geografia e Estatística*).

We used data from the National Mortality System (SIM) and from the Immunization Program (SIPNI), between 17 January and 11 May 2021. The SIM database records all deaths that occur in Brazil. We selected death records with COVID-19 as the underlying cause of death. The SIPNI aims to coordinate immunization actions throughout Brazil, and records the immunobiological doses applied. The number of unvaccinated people was calculated as the difference between the estimated population and the number of vaccinated individuals. We included only individuals who had received at least one COVID-19 vaccine application. After removing duplicates, the databases were probabilistically related by means of people's names (*soundex*) and respective dates of birth, using Stata 15.1 software. The outcome was defined as people who died 21 days or later after the first dose of vaccine. We stratified the vaccinated population by number of doses, vaccine type and age group, and calculated the proportion of deaths as well as the protection ratio for deaths and percentage attributable protection ratio for deaths, and their respective 95% confidence intervals. All data in this study were extracted from secondary databases. The use of data was authorized by the Secretary of Health of the State of Ceará. As the study consisted of an analysis of secondary data, no informed consent was sought.
