Hospitalization and risk of death due to influenza among vaccinated and unvaccinated patients. A 5-year study in the northeastern Mexican population

Figures & data

Table 1. Clinical and demographic characteristics of patients included (ILI and confirmed seasonal influenza) according to the vaccination status.

Characteristic	Vaccinated, n (%)	Unvaccinated, n (%)	p-Value
Total	302 (31.32)	662 (68.67)
Gender
Female	190 (62.91)	361 (54.53)	.0178
Age group (years)
0–8	17 (5.62)	65 (9.81)	.0415
9–17	10 (3.31)	42 (6.34)	.0751
18–49	246 (81.45)	400 (60.42)	.0001
50–64	12 (3.97)	82 (12.38)	.0001
>65	17 (5.62)	68 (10.27)	.0254
No data	0 (0.00)	5 (0.75)	NA
Influenza season
2014–2015	32 (10.59)	76 (11.48)	.7690
2015–2016	19 (6.29)	120 (18.12)	.0001
2016–2017	46 (15.23)	156 (23.56)	.0042
2017–2018	110 (36.42)	154 (23.26)	.0001
2018–2019	95 (31.45)	156 (23.56)	.0120
Antiviral treatment prior assessment
Amantadine	3 (0.99)	16 (2.41)	.2205
Oseltamivir	4 (1.32)	17 (2.56)	.3227
Zanamivir	0 (0.00)	1 (0.15)	NA
High-risk condition^a
Any	4 (8.69)	100 (33.89)	.0001
Asthma/pulmonary	8 (17.37)	117 (39.64)	.0001
Cardiovascular	9 (19.55)	106 (35.92)	.0001
Diabetes	4 (8.69)	82 (27.79)	.0001
Pregnancy	16 (34.78)	57 (19.32)	.0946
Renal	2 (4.34)	24 (8.13)	.0155
Treatment/outcome
Outpatient	256 (84.76)	367 (55.43)
Hospitalized	46 (15.23)	295 (44.56)	.0001
ICU admission	2 (4.34)	82 (27.79)	.0001
In-hospital mortality	0 (0.00)	52 (17.62)	.0001

^aPresence of a high-risk health condition is defined as the presence of ≥1 medical record-documented on the Tenth Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD–10) high-risk code from October 1, 2014, to enrollment, as defined by the Advisory Committee on Immunization Practices (ACIP) guidance for conditions that increase risk for complications from seasonal influenza. The high-risk condition column met more than 100% because some patients had more than one high-risk health condition.

ILI: influenza-like illness; NA: not applicable.

Statistically significant p values are remarked in bold letters.

Table 2. Total of confirmed seasonal influenza cases.

	Vaccinated (n = 302)	Unvaccinated (n = 662)	p-Value
Rapid antigen test positive*	109/302	252/662	.606
RT-PCR positive**	43/93	111/199	.162
Influenza A	9	23	.977
Subtype A H1N1	0	24	.0003
Subtype A H3N2	23	38	.044
Influenza B	11	26	.943
Rapid antigen test and RT-PCR positive	34	73	.764

*All patients were evaluated by the rapid antigen test.

**Selected patients were evaluated by the RT PCR.

RT-PCR: real-time polymerase chain reaction.

Statistically significant p values are remarked in bold letters.

Table 3. Univariate and multivariate analysis of hospitalization, ICU-admission, and in-hospital mortality risk among vaccinated and unvaccinated patients.

Treatment/Outcome	Vaccinated, n (%)	Unvaccinated, n (%)	Univariate analysis			Multivariate analysis
			OR	95% CI	p-Value	OR	95% CI	p-Value
Outpatient	256 (84.76)	367 (55.43)	0.22	0.16–0.32	0.0001	0.15	0.16–0.30	.0001
Inpatient	46 (15.23)	295 (44.56)	1.70	1.16–2.49	0.0059	1.49	3.13–6.30	.0001
Inpatient in the ICU	2 (4.34)	82 (27.79)	8.46	2.01–35.74	0.0036	2.03	3.70–15.96	.0001
In-hospital mortality	0 (0.00)	52 (17.62)	27.17	1.65–446.62	0.0208	18.73	0.00–0.00	.0001

CI: confidence interval; ICU: intensive care unit; OR: odds ratio.

Statistically significant p values are remarked in bold letters.

Table 4. Characteristics of patients who died during the hospitalization due to seasonal influenza or ILI and their complications. All patients were unvaccinated.

Characteristic	n (%)
Total	52 (100.00)
Male gender	35 (67.30)
Age group (years)
0–8	1 (1.96)
9–17	1 (1.96)
18–49	22 (43.13)
50–64	16 (31.37)
>65	11 (21.56)
Influenza season
2014–2015	2 (3.92)
2015–2016	4 (7.84)
2016–2017	26 (50.98)
2017–2018	4 (7.84)
2018–2019	15 (29.41)
High-risk condition^a
Any	20 (39.21)
Diabetes	17 (33.33)
Obesity	16 (31.37)
Cardiovascular	16 (31.37)
Asthma/pulmonary	9 (17.64)
Seasonal influenza cases
Rapid antigen test	4 (7.84)
AH1N1	12 (23.52)
AH3N2	2 (3.92)
Virus A	5 (9.80)
Total	23 (45.08)
Total ILI	28 (54.90)

^aPresence of a high-risk health condition is defined as the presence of ≥1 medical record-documented on the ICD-10 high-risk code from October 1, 2014, to enrollment, as defined by the ACIP guidance for conditions that increase risk for complications from influenza. The high-risk condition column met more than 100% because some patients had more than one high-risk health condition. CI: confidence interval; ILI: influenza-like illness; OR: odds ratio.