The SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) has caused an unprecedented pandemic in human history. To date, more than 6.5 million lives have been lost to COVID-19 (coronavirus disease 2019). Following widespread efforts for COVID-19 vaccination in Brazil, there has been a drastic reduction in COVID-19 deaths, which was particularly evident in the city of Botucatu, SP, Brazil, after a campaign to a mass vaccination. Our objective was to assess the temporal and epidemiological spread of Variants of Concern (VOC) of SARS-CoV-2 in the four weeks preceding the massive vaccination campaign in the municipality. After randomizing 400 samples, Next-Generation Sequencing was used to produce sequences and determine the variants. Among high-quality sequences, 98.4% belonged to the VOC Gamma, with P.1 and P.1.14 being the most prevalent lineages. P.1 was more frequent in both men and women, and in younger individuals and adults (0-59 years) compared to P.1.14. There was no correlation between the variants and the presence of comorbidities or between them and moderate to severe clinical cases of COVID-19 or death. However, P.1 was more frequent than P.1.14 in people with mild forms of the disease and in those who exhibited symptoms. In the phylogenetic analyses, a small cluster of 9 P.1.14 samples containing mutations in ORF1a: M584V and A3620V was observed, which had not been found in any Gamma sequences to date. The importance of genomic surveillance of SARS-CoV-2 is evident in assisting public health decision-making and the management of COVID-19 and other diseases.