Reply letter to “Vaccine effectiveness of recombinant and standard dose influenza vaccines against outpatient illness during 2018–2019 and 2019–2020 calculated using a retrospective test-negative design”

Figures & data

Table 1. NNV for the recombinant and standard-dose vaccines.

Age group	Vaccine	Background rate	Attack rate	ARR	NNV	Difference in NNV
50–64	RIV4	12.9%	1.7%	0.129–0.017 = 0.112	1/0.112 = 8.9	1.1
	SDIV4	12.9%	2.9%	0.129–0.029 = 0.100	1/0.100 = 10.0
65+	RIV4	12.4%	3.0%	0.124–0.030 = 0.094	1/0.094 = 10.6	0.8
	SDIV4	12.4%	3.6%	0.124–0.036 = 0.088	1/.088 = 11.4

ARR, Absolute risk reduction; NNV, Number needed to vaccinate; RIV4, recombinant influenza vaccine; SDIV4, quadrivalent standard-dose influenza vaccine.