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Relationship between Influenza Vaccination Coverage Rate and COVID-19 Outbreak: An Italian Ecological Study.

Correlazione tra tasso di copertura della vaccinazione antinfluenzale e outcomes relativi al COVID-19

Correlation between influenza vaccination coverage rates and COVID-19 outcomes
Univariate correlations between the influenza vaccination coverage rate and (a) seroprevalence for COVID-19, (b) patients hospitalized with symptoms, (c) patients hospitalized in intensive care units or (d) number of deaths attributable to COVID-19.

The lack of specific vaccines or drugs against coronavirus 2019 disease (COVID-19) requires the identification of alternative clinical approaches to reduce the spread of this pandemic disease, also in view of a possible second wave of outbreaks.

In this study, we focused on the hypothesis that the flu vaccine could reduce the spread of COVID-19.
Influenza virus and SARS-CoV-2 share a similar transmission route and also some symptoms, but they strongly differ in terms of severity and mortality in case of infection, and peculiarly, also in terms of age of the groups predominantly affected.
Influenza preferentially affects children and young adults, whereas COVID-19 mainly affects older subjects. One possible explanation is that children and young people have a more reactive immune system, boosted by the exposure to viral agents or to viral antigens contained in many pediatric vaccines (measles, varicella, mumps, rubella, hepatitis B, papilloma virus ...). Vaccines may induce positive “non-specific” immunotherapeutic mechanisms, improving the immune system's ability to react to other pathogens.
In our study we assessed whether influenza vaccination in people over 65 years of age plays a role in reducing the spread of COVID-19 in the Italian population. We compared region by region, vaccination coverage rates with: (1) the number of infections (assessed in terms of seroprevalence of SARS-CoV-2), (2) the number of hospitalizations for COVID-19, (3) the number of patients admitted to intensive care, and (4) the number of deaths attributable to COVID-19.
In the analysis some possible confusing factors were taken into consideration, and in particular: 1) the percentage of health expenditure compared to the regional gross domestic product, 2) the average seasonal temperature for each region/autonomous province, 3) the delay in the application of the lockdown, 4) import/export Italy-China, 5) international air traffic, 6) mortality due to cardiovascular causes and 7) mortality due to respiratory diseases. Even after adjustment of the analyses for these confounders, all the relationships observed in the univariate analysis were confirmed (all p < 0.01).
In conclusion, our data support the hypothesis that influenza vaccination can help prevent the spread of COVID-19. It would therefore be important to encourage as much as possible any activity that could lead to an increase in vaccination coverage, especially among the over-65s.


Vaccines (Basel). 2020 Sep 16;8(3):E535. doi: 10.3390/vaccines8030535. PMID: 32947988




Damiano Baldassarre, damiano.baldassarre@unimi.it





02 October 2020
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