Reply to letter to editor by Hadigal et al. regarding the immunogenicity and safety trial of high-dose influenza vaccine in adults aged ≥60 years

Figures & data

Table 1. Number needed to vaccinate in high-dose trivalent influenza vaccine (IIV3-HD) vs standard-dose trivalent vaccine (IIV3-SD), using season-specific attack rate in the USA.

Season	Vaccination status	Attack rate in participants*	Background attack rate†	Absolute risk reduction (ARR)	Number needed to vaccinate (NNV)	Delta of NNV: (IIV3-SD – IIV3-HD)
2011/12	Vaccinated with IIV3-HD	0.00317 (23/7253)	–	0.00700 (1.02%/0.00317)	143 (1/0.00700)	86 (229–143)
	Vaccinated with IIV3-SD	0.00580 (42/7244)	–	0.00437 (1.02%/0.00580)	229 (1/0.00437)
	Unvaccinated	–	1.02% (0.00580/[1–43%^Citation6)	–	–	–
2012/13	Vaccinated with IIV3-HD	0.02346 (205/8737)	–	0.01654 (4.00%/0.02346)	60 (1/0.01654)	36 (96–60)
	Vaccinated with IIV3-SD	0.02960 (259/8749)	–	0.01040 (4.00%/0.02960)	96 (1/0.01040)
	Unvaccinated	–	4.00% (0.02960/[1–26%^Citation7)	–	–	–

* Derived from Supplementary Appendix, Table S9 of IIV3-HD trial.⁴

† Calculation: attack rate in participants receiving IIV3-SD/(1 – vaccine effectiveness reported by CDC for the corresponding season); as a result, the effectiveness of IIV3-SD in the IIV3-HD trial equals the CDC reported estimates.^6,7

The U.S. Centers for Disease Control and Prevention (CDC). Seasonal Influenza Vaccine Effectiveness, 2011-2012. 2018. https://www.cdc.gov/flu/vaccines-work/2011-2012.html.

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The U.S. Centers for Disease Control and Prevention (CDC). Seasonal Influenza Vaccine Effectiveness, 2012-2013. 2018. https://www.cdc.gov/flu/vaccines-work/2012-2013.html.

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DiazGranados CA, Dunning AJ, Kimmel M, Kirby D, Treanor J, Collins A, Pollak R, Christoff J, Earl J, Landolfi V, et al. Efficacy of high-dose versus standard-dose influenza vaccine in older adults. N Engl J Med. 2014;371(7):635–645. doi:10.1056/NEJMoa1315727.

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