Association between Exposure to Influenza Vaccination and COVID-19 Diagnosis and Outcomes

Abstract

We explored whether influenza vaccination (IV) affects susceptibility to SARS-CoV-2 infection and clinical outcomes in COVID-19 patients in 17,608 residents of the Italian province of Reggio Emilia undergoing a SARS-CoV-2 test. Exposure to IV was ascertained and the strength of the association with SARS-CoV-2 positivity expressed with odds ratios (OR). Rates of hospitalisations and death in those found positive were assessed and hazard ratios (HR) were estimated. The prevalence of IV was 34.3% in the 4885 SARS-CoV-2 positive and 29.5% in the 12,723 negative subjects, but the adjusted OR indicated that vaccinated individuals had a lower probability of testing positive (OR = 0.89; 95% CI 0.80–0.99). Among the 4885 positive individuals, 1676 had received IV. After adjusting for confounding factors, there was no association between IV and hospitalisation (1.00; 95% CI 0.84–1.29) or death (HR = 1.14; 95% CI 0.95–1.37). However, for patients age ≥65 vaccinated close to the SARS-CoV-2 outbreak, HRs were 0.66 (95% CI: 0.44–0.98) and 0.70 (95% CI 0.50–1.00), for hospitalisation and death, respectively. In this study, IV was associated with a lower probability of COVID-19 diagnosis. In COVID-19 patients, overall, IV did not affect outcomes, although a protective effect was observed for the elderly receiving IV almost in parallel with the SARS-CoV-2 outbreak. These findings provide reassurance in planning IV campaigns and underscore the need for exploring further their impact on COVID-19.

Impact of the influenza vaccine on COVID-19 infection rates and severity

“…This is a slight contradiction to a recent report from Italy demonstrating the greatest protection against COVID-19 in elderly patients who received the vaccine in close proximity to COVID-19 exposure as compared to several months before. 14 While we did see decreased mortality in the influenza vaccinated group, the association was non-significant. This may be due to a small sample size and the low number of deaths observed.…”

“…Recent studies have suggested that prior vaccination to pathogens such as tuberculosis and influenza may confer some protection against COVID-19. 9 , 10 , 11 , 12 , 13 , 14 An analysis of over 92,000 COVID-19 patients in a non-peer reviewed study from Brazil found a 17% reduced odds of mortality, 8% lower odds of need for intensive care treatment and 18% lower odds of invasive respiratory support in those who received an influenza vaccine. 12 Separate epidemiologic studies in Italy and the United States found a correlation between increased vaccination rates in those aged greater than 65 years and decreased rates of COVID-19 deaths across different regions.…”

Effect of influenza vaccine on COVID-19 mortality: a retrospective study

“…Interestingly, in an epidemiological study performed on an Italian population, the flu vaccine was associated with reduced susceptibility to COVID-19. However, in this study, the death rate was affected by flu vaccination only in a small group of patients who received the vaccine in the period immediately preceding the onset of the outbreak [11]. In our study, we only included symptomatic patients who presented themselves to the Emergency Department.…”

“…The hypothesized pathophysiological mechanisms underlying the interaction between influenza vaccine and coronavirus infection are structural similarities in ligands for cell receptors, antibody cross-reactivity, and a non-specific cell-mediated response [4,[7][8][9]. Several authors have studied the effect 1 3 of influenza (flu) and pneumococcal vaccination on the susceptibility and mortality of COVID-19, with conflicting results [10,11]. This is why we have designed a study aimed at verifying whether influenza vaccination may influence the clinical course of COVID-19.…”

Absence of association between 2019–20 influenza vaccination and COVID-19: results of the European I-MOVE-COVID-19 primary care project, March–August 2020

“…7 Additionally, ecological studies correlating influenza vaccination uptake rates and COVID-19 mortality, published in scientific journals as articles or rapid responses to articles sustain these hypotheses. 8,9 Conversely, several articles have been published in scientific journals on the negative association or no association between influenza vaccination and COVID-19 mortality, hospitalisation and infection, 10,11 many of which are summarised in a recent systematic literature review. [12][13][14][15] The authors of the latter paper recommend that further studies are carried out to validate these preliminary findings across settings.…”