End of season 2022/2023 quadrivalent influenza vaccine effectiveness in preventing influenza in primary care in Portugal

Figures & data

Figure 1. Participants exclusion flowchart.

Figure 2. Weekly distribution of laboratory-confirmed influenza-positive ILI cases and influenza-negative controls, Portugal, 2022/2023 season.

Table 1. Characteristics of laboratory-confirmed influenza cases and influenza-negative controls, Portugal, week 41/2022-week 14/2023.

	Laboratory-confirmed influenza cases (n = 218)		Influenza-negative controls (n = 374)
Characteristics	n	%	n	%	p-value
Age group (years)					p = .009
18–44	123	56.4	184	49.2
45–64	82	37.6	138	36.9
≥65	13	6.0	52	13.9
Sex					p = .002
Female	135	61.9	277	74.1
Male	83	38.1	97	25.9
Any chronic condition*					p = .002
No	173	79.4	252	67.4
Yes	45	20.6	122	32.6
Month of symptoms onset					p < .001
October	20	9.2	72	19.3
November	97	44.5	99	26.5
December	53	24.3	71	19.0
January	22	10.1	78	20.9
February	12	5.5	29	7.8
March	10	4.6	20	5.4
April	4	1.8	5	1.3

*diabetes type 1, diabetes type 2, hypertension, cardiovascular disease (excluding hypertension), chronic renal disease, chronic liver disease, neuromuscular disease, immunodeficiency (congenital or acquired), obesity, asthma under medical treatment, chronic respiratory disease (excluding asthma), cancer.

Table 2. Interim influenza vaccine effectiveness against any influenza and A (H3N2) influenza, Portugal, week 41/2022-week 14/2023.

	Laboratory-confirmed influenza cases n (%)		Negative controls n (%)		VE (%)*	95% CI
	Vaccinated	Unvaccinated	Vaccinated	Unvaccinated
Any influenza	20 (9.2)	198 (90.8)	79 (21.2)	295 (78.9)	59.3	(27.3 to 77.3)
A(H3N2)	19 (11.4)	148 (88.7)	79 (21.2)	295 (78.9)	44.5	(−5.6 to 70.8)

*adjusted by age group, sex, chronic condition, and month of symptoms onset. VE: vaccine effectiveness; 95% CI: 95% confidence interval.