A case study investigating the effects of emergency vaccination with Brucella abortus A19 vaccine on a dairy farm undergoing an abortion outbreak in China

Table 4 The influence of parity on estimates of vaccine (Brucella abortus A19) effectiveness for preventing abortions

Parity	Year	Incidence of abortion (95% CI), %	Relative risk (95% CI)	p value^†	Percent vaccine effectiveness (95% CI), %
1^st parity
	2018	22.8 (14.1, 33.6)	1.00 (reference)	0.012	86.7 (4.4, 98.1)
	2020	3.0 (0.1, 15.8)	0.13 (0.02, 0.96)	0.012	86.7 (4.4, 98.1)
2^nd parity
	2018	30.3 (15.6, 48.7)	1.00 (reference)	0.072	63.3 (0.0, 87.3)
	2020	11.1 (3.1, 26.1)	0.37 (0.13, 1.06)	0.072	63.3 (0.0, 87.3)
≥ 3^rd parity
	2018	8.3 (1.0, 27.0)	1.00 (reference)	0.686	Not applicable
	2020	15.6 (5.3, 32.8)	1.88 (0.40, 8.85)	0.686	Not applicable
All parities
	2018	22.1 (15.4, 30.0)	1.00 (reference)	0.013	56.8 (15.8, 77.8)
	2020	9.9 (4.9, 17.5)	0.43 (0.22, 0.84)	0.013	56.8 (15.8, 77.8)

^†Fisher’s exact test; Relative risk, incidence of abortion compared to that in each category