Projected impact of a plant-derived vaccine on the burden of seasonal influenza in Canada

Figures & data

Table 1. Description of scenario analyses

Description of scenario	Scenario number
Variation in VE: To account for seasonal variation in the effectiveness of influenza vaccines, two scenarios considered variation in VE from base case inputs for the plant-derived QVLP and egg-derived vaccines.	Scenario 1: 5% absolute decrease in VE
	Scenario 2: 5% absolute increase in VE
Variation in VC: An online survey among the general adult population in the provinces of Alberta, British Columbia, Ontario, and Quebec (n = 802) was conducted in December 2019 and projected a 6.73% increase in VC with the introduction of plant-derived vaccines versus currently available egg-derived vaccines. Four scenarios considered the impact of greater vaccine uptake from base case inputs with the plant-derived QVLP vaccine option only.	Scenario 3: 3% absolute increase in VC
	Scenario 4: 5% absolute increase in VC
	Scenario 5: 6.73% absolute increase in VC
	Scenario 6: For the 18–64 population only; absolute increase of 3% in VC applied proportionally among those aged 18–49 and 50–64 based on projections from the online survey, to account for the likelihood that VC increases would vary by age group
Simultaneous variation in VE and VC: Seasonal influenza vaccines had relatively low VE during the 2017/18 and 2018/19 seasons (CDC 2020).^Citation34 To simulate the impact of increased VC during seasons when VE is not particularly low, two scenarios examined simultaneous variation in VC and VE from base case inputs.	Scenario 7: VE of plant-derived QVLP vaccines assumed to be equal to that of egg-derived vaccines and an absolute increase in VC of 3% applied to plant-derived QVLP vaccines only
	Scenario 8: 5% absolute increase in VE applied to the both plant-derived QVLP and egg-derived vaccines, and a 3% absolute increase in VC applied to plant-derived QVLP vaccines only
Variation in attack rates: A scenario analysis considered attack rates sourced from Molinari et al.^Citation24 This study estimated baseline attack rates in the adult population using data for multiple influenza seasons spanning 1983–1989 and 1998–1999.	Scenario 9: Attack rate inputs of 7% among the population aged 18–64 years and 9% among those aged 65+ years

QVLP: quadrivalent virus-like particle; VC: vaccine coverage; VE: vaccine effectiveness.

Table 2. Number of influenza cases and influenza-related outcomes in the Canadian population aged 18–64 and 65+ with no vaccines, egg-derived vaccines only, and plant-derived QVLP vaccines only – base case results

Scenario	Influenza cases	Symptomatic cases	GP visits	ED visits	Inpatient admissions	ICU admissions	Deaths
18–64 subgroup
No vaccine (95% CrI]	2,006,829 (1,782,819–2,250,071)	1,685,736 (1,497,568–1,890,059)	766,075 (640,164–902,349)	38,036 (28,565–48,654)	20,805 (12,769–30,751)	3940 (2359–5968)	1187 (652–1872)
Egg-derived vaccines (95% CrI)	1,827,859 (1,630,525–2,037,601)	1,535,402 (1,360,421–1,723,350)	698,012 (582,476–823,953)	34,774 (26,056–44,534)	19,022 (11,643–28,249)	3602 (2157–5459)	1088 (596–1717)
Plant-derived QVLP vaccines (95% CrI)	1,779,830 (1,577,677–2,004,607)	1,495,057 (1,325,249–1,683,870)	680,731 (567,415–802,449)	34,379 (25,798–44,221)	18,815 (11,453–28,050)	3563 (2119–5421)	1083 (597–1711)
65+ subgroup
No vaccine (95% CrI)	639,456 (570,221–711,464)	537,143 (478,986–597,630)	461,719 (403,962–521,594)	48,398 (34,104–65,485)	27,137 (14,131–43,725)	4376 (2198–7199)	7513 (3850–12,186
Egg-derived vaccines (95% CrI)	579,685 (464,494–672,924)	486,935 (390,313–564,010)	418,557 (332,502–491,588)	43,875 (28,881–60,584)	24,591 (12,169–40,164)	3965 (1931–6595)	6809 (3386–11,175)
Plant-derived QVLP vaccines (95% CrI)	551,766 (438,160–646,895)	463,484 (368,054–543,392)	398,413 (314,501–473,544)	41,785 (27,537–58,149)	23,425 (11,675–38,421)	3778 (1824–6267)	6483 (3222–10,717)

CrI: credible interval; ED: emergency department; GP: general practitioner; ICU: intensive care unit; QVLP: quadrivalent virus-like particle. Results represent the mean of 5000 simulations. Influenza cases refers to the total number of symptomatic and asymptomatic influenza cases combined. Symptomatic cases refers to the total number of symptomatic influenza cases only.

Figure 1. Number of prevented influenza cases and influenza-related outcomes with plant-derived QVLP and egg-derived vaccines versus no vaccination in the base case analysis among the Canadian population (a) aged 18–64; and (b) aged 65+

ED: emergency department; GP: general practitioner; ICU: intensive care unit. Results represent the mean of 5000 simulations. Influenza cases refers to the total number of symptomatic and asymptomatic influenza cases combined. Symptomatic cases refers to the total number of symptomatic influenza cases only.

Figure 2. Number of (a) prevented cases, (b) prevented inpatient admissions, and (c) prevented deaths with plant-derived QVLP and egg-derived vaccines versus no vaccination in the base case analysis among the adult Canadian population stratified by age

Results represent the mean of 5000 simulations. Prevented influenza cases refers to the total number of symptomatic and asymptomatic influenza cases combined.

Figure 3. Difference in the number of prevented influenza cases with plant-derived QVLP and egg-derived vaccines in scenario analyses relative to respective base case results among the Canadian population (a) aged 18–64^a,b and (b) aged 65+.^a–c

NA: not applicable; VE: vaccine effectiveness; VC: vaccine coverage. ^aVariations in VE and VC are reported relative to the base case analyses input parameters; Scenario 6 was only performed for the 18–64 population. ^bBase case attack rate obtained from the RCT was 8% and 11% in those aged 18–49 and 50–64, respectively. ^cBase case attack rate was assumed to be 11% in those aged 65+. Results represent the mean of 5000 simulations. The numbers of cases prevented with egg-derived vaccines in scenarios 3–6 converge around zero (i.e., do not equal zero) due to the underlying uncertainty in input point estimates, as a full simulation was run for each set of results.

CDC. “CDC Seasonal Flu Vaccine Effectiveness Studies”. 2020 [accessed 17 Jul 2020]. https://www.cdc.gov/flu/vaccines-work/effectiveness-studies.htm .

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