#16,189
In July, and again in early August (see PLoS One: Potential Benefits of the Influenza Vaccine Against SARS-CoV-2 (Retrospective Cohort Analysis)) we looked at a study that found that those who received a flu vaccine within 6 months of contracting COVID appeared significantly less likely to experience severe disease.
Previously, we'd seen a few studies suggesting that - at least statistically - receipt of the flu vaccine had been linked to lower SARS-CoV-2 infection rates, and/or reduced severity.
A few of those studies include:
- In 2020, in the preprint The effect of influenza vaccination on trained immunity: impact on COVID-19, researchers from the Netherlands hypothesized that receipt of the quadrivalent flu vaccine could boost innate immunity after finding SARS-CoV-2 infection `. . . was less common among Dutch hospital employees who had received influenza vaccination during the 2019/2020 winter season (RR = 0,61 (95% CI, 0.4585 - 0.8195, P = 0.001).'
- Similarly, last January researchers from the University of Missouri School of Medicine published The Flu Vaccination May Have a Protective Effect on the Course of COVID-19 in the Pediatric Population, finding that children vaccinated against flu were less likely to be symptomatically infected with SARS-CoV-2 (p=0.028, adj. OR=0.714, 95% CI [0.529, 0.964]) than those not vaccinated
- And yet another study, Inactivated trivalent influenza vaccination is associated with lower mortality among patients with COVID-19 in Brazil, looking at over 53,000 hospitalized COVID patients during the first half of 2020, found mortality was consistently lower among patients who received a flu vaccine after March 1st, 2020.
- And last March, in AJIC: Impact of the Influenza Vaccine on COVID-19 Infection Rates and Severity, we saw another study that found that receipt of the flu vaccine appears to be linked to reduced infection, and severe illness, with COVID-19.
This is often referred to as the `temporary immunity hypothesis'.
Adding to this growing list we have a new preprint that finds a statistical correlation between hospital employees receiving the quadrivalent flu shot and their having a lowered risk of COVID infection.
Interestingly, it also demonstrates that receipt of the flu vaccine strongly downregulates nearly 370 inflammatory proteins while boosting anti-inflammatory proteins, which could help explain the reduced severity of COVID in that cohort.
The link, Abstract, and link to the 27-page PDF follow. I'll have a brief postscript when you return.
Induction of trained immunity by influenza vaccination - impact on COVID-19
Priya A. Debisarun, Katharina L. Gössling, Ozlem Bulut, Gizem Kilic, Martijn Zoodsma, Zhaoli Liu, Marina Oldenburg, Nadine Rüchel, Bowen Zhang, Cheng-Jian Xu, Patrick Struycken, Valerie A.C.M. Koeken, Jorge Domínguez-Andrés, Simone J.C.F.M. Moorlag, Esther Taks, Philipp N. Ostermann, Lisa Müller,Heiner Schaal, Ortwin Adams, Arndt Borkhardt, Jaap ten Oever, Reinout van Crevel, Yang Li, Mihai G. Netea
doi: https://doi.org/10.1101/2021.09.03.21263028
This article is a preprint and has not been peer-reviewed [what does this mean?]. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.
ABSTRACT
Non-specific protective effects of certain vaccines have been reported, and long-term boosting of innate immunity, termed trained immunity, has been proposed as one of the mechanisms mediating these effects. Several epidemiological studies suggested cross-protection between influenza vaccination and COVID-19.
In a large academic Dutch hospital, we found that SARS-CoV-2 infection was less common among employees who had received a previous influenza vaccination: relative risk reductions of 37% and 49% were observed following influenza vaccination during the first and second COVID-19 waves, respectively.
The quadrivalent inactivated influenza vaccine induced a trained immunity program that boosted innate immune responses against various viral stimuli and fine-tuned the anti-SARS-CoV-2 response, which may result in better protection against COVID-19. Influenza vaccination led to transcriptional reprogramming of monocytes and reduced systemic inflammation.
These epidemiological and immunological data argue for potential benefits of influenza vaccination against COVID-19, and future randomized trials are warranted to test this possibility.
While certainly no substitute for getting the COVID vaccine, we continue to see studies which appear to show some additional, and unexpected, benefits against severe illness from SARS-CoV-2 infection.
Despite its often lackluster effectiveness - particularly in my age group (65+) - I get flu vaccine every year because even a little protection can be lifesaving. The downsides of doing so are miniscule and it not only helps to protect me, it helps to protect others.
We've also seen evidence over the past few years that influenza - and other respiratory viruses - can trigger heart attacks and strokes (see JAHA: Another Study Linking ILI To Increased Risk Of Heart Attack & Stroke), and that getting the flu shot can substantially reduce those risks as well.
The evidence that it may help prevent, or attenuate, COVID-19 may not be robust, but there continues to be enough of a pattern in the data to warrant further research.
