While much of the focus on treating COVID-19 and preventing its spread has been on antibodies, emerging research is indicating that T cells of the adaptive immune system are equally important to not only disease resistance and vaccine development but also to epidemiological tracking. Researchers at Karolinska Institute assert that recent T cell immunity testing done in a study there reveals that the number of COVID-19 cases is about double what estimates made based on earlier seroprevalence antibody testing had indicated. Results just released from a T cell immunity study from Germany suggests that perhaps 80% of the population may carry COVID-19 resistance acquired from exposure to some of the other four coronaviruses that cause common colds. If correct, such results have clear implications for achievement of more accurate estimates of both infection lethality rates and of timeframes for achieving herd immunity with and without a safe and effective vaccine. The high degree of COVID‑19 resistance in those too young to benefit from either antibodies or T cells is also discussed.