The Impact of the First Year of COVID-19 Vaccination Strategy in Brazil: An Ecological Study

Abstract

Background: Countries have used different strategies to prioritize who be vaccinated first during the COVID-19 vaccination roll-out. No consensus exists about the best strategy to be adopted by low-and-middle-income countries with limited access to vaccines. Brazil adopted an age-based calendar strategy to reduce mortality and the burden over the healthcare system. The impact of this strategy on preventing deaths and years of life lost was not estimated.

Methods: This ecological study analyses the dynamic of vaccination coverage and COVID-19 deaths in adults (≥20 years) during the first year of the COVID-19 vaccination roll-out (January-December, 2021) using nationwide data (DATASUS). We stratified the adult population into 20-49, 50-59, 60-69, and 70+ years. The dynamic effect of the vaccination campaign on mortality rates was estimated using Differences-in-Differences. The prevented and preventable deaths (observed deaths higher than expected), and Potential Years of Life Lost (PYLL), for each age group were obtained in a counterfactual analysis. 

Findings: During the first year of COVID-19 vaccination 266,153,517 doses were administered, achieving 91% first-dose coverage. 380,594 deaths were reported, being 154,091 (40%) in 70+, and 136,804 (36%) from 50-59 or 20-49 years. The mortality rates of 70+ decreased 52% (RRR [95% CI]: 0.48 [0.43-0.53]) in 6 months, whereas rates for 20-49 were still increasing due to the low coverage (52%). The vaccination roll-out strategy prevented 59,618 deaths, 53,088 (89%) from those aged 70+ years. However, the strategy did not prevent 54,797 deaths, 85% from those under 60 years, being 26,344 (45%) only in 20-49, corresponding to 1,589,271 PYLL, being 1,080,104 PYLL (68%) from those aged 20-49 years.

Interpretation: The adopted aged-based calendar vaccination strategy initially reduced the mortality in the oldest, but did not significantly prevent the deaths of the youngest. Countries with high burden, limited vaccine supply and young population should consider other factors besides age to prioritise who to vaccine first.

Funding Information: This work is part of the Grand Challenges ICODA pilot initiative, delivered by Health Data Research UK and funded by the Bill & Melinda Gates Foundation and the Minderoo Foundation. This study was supported by the National Council for Scientific and Technological Development (CNPq), the Coordination for the Improvement of Higher Education Personnel (CAPES) - Finance Code 001, Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ) and the Pontifical Catholic University of Rio de Janeiro. OTR is funded by a Sara Borrell grant from the Instituto de Salud Carlos III (CD19/00110). OTR acknowledges support from the Spanish Ministry of Science and Innovation and State Research Agency through the "Centro de Excelencia Severo Ochoa 2019-2023" Program (CEX2018-000806-S), and support from the Generalitat de Catalunya through the CERCA Program.

Declaration of Interests: The authors declare no potential conflicts of interest.

Ethics Approval Statement: Data was publicly available, anonymized, and de-identified. Following ethically agreed principles on open data, this analysis did not require ethical approval in Brazil.