The speed with which the pandemic swept across the world meant that even in countries with sophisticated health systems, mortality was difficult to accurately assess, especially in the early days. Patients with heart disease, diabetes, cancer and other chronic conditions are at greater risk of dying from Covid-19. Some governments, including Russia, had last year attributed the cause of deaths in some of these patients to the pre-existing condition, raising doubts about the veracity of official mortality data.
Tens of thousands of probable Covid-19 deaths in the U.S. weren’t captured by official statistics between March and May 2020, a study in July found.