Estimations of the infection mortality rate of COVID-19, the disease caused by the SARS-CoV-2 virus, are prone to biases due to underdiagnosis, false positives, false negatives, and time lag between diagnosis and death. With a systematic analysis that combines epidemiological modeling of COVID-19 in Spain and in the state of New York, and results of random immunological testing in the spring of 2020 in both locations, most of the bias is eliminated and any remaining bias is evaluated and reported as an uncertainty estimate. A true infection mortality rate of 1.45 ± 0.45 % is obtained, representing an average for the two locations, and obtained with a different technique to minimize the effect of potential biases. In the absence of specific local data, this number can be used for the first wave of COVID-19 in OECD countries. This mortality rate estimate of the new coronavirus is sufficiently accurate to be used as a basis for policy decisions. When differences in age distribution between Spain and the state of New York are accounted for, tentative infection mortality rates of 1.18 ± 0.26 % and 1.94 ± 0.43 % are put forward for New York and Spain, respectively.