Table A4. Comparison of the frequency of deaths stratified by vaccination history, according to data from 19th- and early 20th-century outbreaks.

Reference	Unvaccinated		Vaccinated
	Cases	Deaths	Cases	Deaths	p value*	OR (95% CI)†
Welch (10), 1878	7	7	39	7	<0.01	NC
van der Willigen (3), 1893–1894	2	2	78	10	0.02	NC
Rao (6), 1959–1962	12	9	82	17	<0.01	11.5 (2.8–47.1)

*2-sided.
†OR, odds ratio; CI, confidence interval; NC, not calculable.