Fig. 1: Vaccination, infection and basic reproductive ratio of SARS-CoV-2 in Brazil, France, Germany, Israel, the United Kingdom and the United States.

a, Large-scale vaccination programmes commenced in December 2020. At the peak, Israel vaccinated more than 20,000 people per million (2%) per day. The vaccination rate decreased in April 2021 after most eligible individuals had been vaccinated. b, In an attempt to balance economic and sanitary considerations, these six countries have gone through several cycles of loosening and tightening government-imposed restrictions, resulting in periodical increases and decreases in the number of new infections per day. The Alpha variant, identified in November 2020, is most probably responsible for the increase in the number of infections in the United Kingdom and Israel at that time. The fourth wave in Israel (starting in July 2021) has been attributed to a combination of the emergence of the Delta variant and waning of immunity after vaccination. c, Vaccination in most countries follows a logistic-shaped curve. At first, priority groups are vaccinated. Then, most of the population is vaccinated in a short time frame (exponential growth). Lastly, the total number of vaccinated individuals plateaus due to vaccine hesitancy and ineligibility of the remaining non-vaccinated individuals. d, The reproductive ratio of SARS-CoV-2 infections has hovered around 1 in the six considered countries due to the imposition of non-pharmaceutical interventions to curb the infection rates. Hence, the number of infections per day has fluctuated around an average for the duration of the pandemic.