The COVID-19 pandemic halted longevity improvements and mortality reductions at older ages in 2020. Life expectancy at birth - a widely-used indicator of population health - declined from 2019 to 2020 in 24 out of 26 countries for which high-quality vital statistics are presently available, including most European countries, Chile and the USA. Males in the USA and Bulgaria experienced the largest losses in life expectancy at birth during 2020 (2.1 and 1.6 years respectively), but staggering reductions of more than an entire year were documented in eleven countries for males, and seven among females; a magnitude of loss not witnessed since WW-II in many countries. Reductions were mostly attributable to increased mortality above age 60 and to official COVID-19 deaths.