The effect of influenza vaccine in reducing the severity of clinical outcomes in patients with COVID-19: a systematic review and meta-analysis

Abstract

Recent evidence suggests that vaccination against influenza may reduce the clinical outcomes of COVID-19. This study looked at the link between influenza vaccination and the severity of COVID-19 infection. We searched five databases until August 2021. We included studies that reported the relationship between influenza vaccination and COVID-19 outcomes. We pooled the data as risk ratio (RR) or mean difference (MD), with 95% confidence intervals (CIs), the data pooled using fixed and random effects models according to the heterogeneity of results. Sixteen observational studies with 191,496 COVID-19 patients were included. In terms of mechanical ventilation, our analysis showed a significant favor for the influenza vaccinated group over the non-vaccinated group (RR = 0.72, 95% CI [0.54, 0.96], P = 0.03). However, the analysis indicated no statistically significant differences between vaccinated and non-vaccinated groups in the term of mortality rate (RR = 1.20, 95% CI [0.71, 2.04], P = 0.50), hospital admissions (RR = 1.04, 95% CI [0.84, 1.29], P = 0.75), intensive care admissions (RR = 0.84, 95% CI [0.44, 1.62], P = 0.60). There were no significant differences between those who had received the influenza vaccine and those who had not in COVID-19 clinical outcomes, except for mechanical ventilation which showed a significantly lower risk in the influenza vaccinated group compared to the non-vaccinated one. However, future research is encouraged as our data have limitations, and the influenza vaccine is regularly updated. Also, this does not exclude the importance of the influenza vaccine during the COVID-19 pandemic.

Predicting infection with COVID-19 disease using logistic regression model in Karak City, Jordan

“…A meta-analysis study revealed a significant advantage for mechanical ventilation in COVID-19 individuals who had received an influenza vaccination over those who had not. 33 Another meta-analysis of observational studies included 290,327 participants claimed that receiving an influenza vaccination decreases the chance of COVID-19 infection which is in agreement with the findings of our study. 34 On the other hand, the relationship between the influenza vaccine and a decreased risk of COVID-19 negative outcomes was discussed by Fink et al 35 This included the ability of live vaccines to activate trained innate immunity and produce known "off-target" protection against infections other than those specifically targeted by the vaccine.…”

Seasonal Influenza Vaccine Intention among Nurses Who Have Been Fully Vaccinated against COVID-19: Evidence from Greece

“…Additionally, systematic reviews have identified that influenza vaccination is a cost-saving or cost-effective intervention [ 9 , 10 ]. Moreover, a recent meta-analysis [ 11 ] showed that influenza vaccination was associated with a reduced risk of mechanical ventilation among COVID-19 patients, while another meta-analysis [ 12 ] showed a lower risk of COVID-19 infection and influenza leading to hospitalization among the vaccinated group compared to the non-vaccinated group.…”

Examining the effectiveness and duration of adjuvanted vs. non‐adjuvanted influenza vaccines in protecting older adults against symptomatic SARS‐CoV‐2 infection

“…Nevertheless, these findings were limited to the first wave of the pandemic and did not therefore account for a larger spectrum of disease severity. Finally, the available meta‐analyses 6,26 have reported contrasting results in terms of different COVID‐19‐related outcomes, underlying a high level of heterogeneity among the included studies. In this regard, the presence of bias due to the ‘healthy vaccinee’ effect has been demonstrated as a major source of inconsistencies among previous studies 7 …”