Table 1.

Features of 20th and 21st century influenza pandemics

Pandemic	Dates	Influenza virus	No. waves	No. deaths	Age groups with highest mortality
Spanish influenza	1918–1920	A/H1N1	3(Barry, 2005)	20–100 million (Barry, 2005, Johnson and Mueller, 2002, Jordan, 1927, Nicholson et al., 2019)	Infants, young adults (20–40 years), elderly (Taubenberger and Morens, 2006)
Asian influenza	1957–1958	A/H2N2	2(Rogers 2020)	1–2 million (Saunders-Hastings and Krewski, 2016)	Infants, children (5–14 years), young adults (15–24 years), elderly (Viboud et al., 2016)
Hong Kong influenza	1968–1969	A/H3N2	2(Cockburn et al., 1969, Saunders-Hastings and Krewski, 2016)	0.5–2 million (Saunders-Hastings and Krewski, 2016)	>65 years (Centers for Disease Control and Prevention 2019b)
Russian influenza	1977–1979	A/H1N1	1(Gregg et al., 1978)	700,000 (Gregg et al., 1978)	Infants, young adults (<25 years) (Gregg et al., 1978)
Swine influenza	2009–2010	A/H1N1pdm09	2 or 3 depending on location(Jhung et al., 2011, Saunders-Hastings and Krewski, 2016)	123,000–203,000 (Simonsen et al., 2013)	5–59 years (Charu et al., 2011)