Cases grew rapidly in both host and non-host states during the first 2 weeks of competition, reaching 600 cases per million in parts of the country. This elevated rate continued during the remaining 2 weeks of the tournament (Fig. 1).

COVID’s high rate of asymptomatic cases together with Copa América’s compulsory testing prevented meaningful comparisons of incidence rates between the general population and the tournament (see ESM 3) [8,9,10,11,12,13,14]. Therefore, we analysed the number of positive tests within each group of accredited personnel.

Of the 179 positive tests reported during the tournament, we estimate that 98 were the product of exposure during Copa América. This estimate is based on the exclusion of positive tests reported during the first week of the tournament (see Fig. 1). Games during this first calendar week of the tournament were held 5 days apart, on June 13 and June 18. Considering the accuracy of Rt-qPCR early after exposure to the virus, it is reasonable to assume that positive cases detected during the first week are the product of contagion occurring prior to the beginning of Copa América (see ESM 4) [13, 15]. Importantly, the compulsory testing during Copa América prevented any infection occurring during the first week from remaining undetected during the second week of the tournament.

Cases in bubbles decreased during the tournament, showing protocols were effective in preventing uncontrolled spread. Considering the unfavourable local epidemiological scenario in Brazil, the bubbles were effective in isolating the tournament from the rest of the country (Fig. 1). Two cases were detected in the CONMEBOL staff and referees bubble during the final week. Protocols were followed and those affected were promptly isolated to avoid further spread.

To better understand the risks involved for local staff, and by extension the communities they live in, we analysed whether contagion in this group exceeded expectations (see ESM 3). Because direct comparison of incidence rates was not feasible due to Copa América’s compulsory testing programme, we established a baseline for contagion based on seroprevalence studies conducted at the time in Brazil [9, 16]. Seroprevalence varied significantly with estimates for 2021 ranging from 17 to 35%, with large variations observed across the country [9, 17,18,19,20,21] (see ESM 4). The 83 positive cases detected from the second week of the tournament onwards represent 33.2% of local staff. This infection rate was comparable to the observed seroprevalence in Brazil at the time, suggesting that the risk for members of the local staff was not in excess of what they were exposed to in the general population.