The latest report by the International Committee for the Recovery of the Vaquita (CIRVA) estimates that only between 6 and 22 individuals remained alive in 2018. It is likely, however, that there no more than 10 vaquitas left. (For comparison, in 1997, the population was estimated to be about 600 individuals strong.)
However, these estimates based on acoustic and very few visual surveys, and with a population size this small, it is very difficult to arrive at an accurate number. The click detectors (“C-pods”) used to detect the presence of vaquita in the surveyed area have some limitations and are subject to vandalism and failure. CIRVA, in its report, recommends the purchase of additional C-pods to improve the accuracy.