Flue Vaccination does not Protect Against COVID-19 Infection; A Cross-Sectional Study.

is likely be the nal solution to stop the COVID-19 pandemic which has been considered as a global public health emergency. Inuenza and corona viruses have previously demonstrated antigenic cross-reactivity. This cross-sectional study was aimed to evaluate the transmission rate and the severity of corona virus infection among health care workers with history of previous inuenza vaccination. Subjects of the study were asked about their demographics, inuenza vaccination history prior to pandemic, infection with Covid-19 and the severity parameters of the disease.


Introduction SARS-COV-2 or COVID-19 virus infection was initially identi ed in Wuhan City, China in December 2019
and became a public health emergency of international concern (PHEIC). To date, the burden brought by this pandemic has accounted to 25 million con rmed cases and 855 thousand deaths worldwide because of rapid geographical transmission and severity of the disease [1] . COVID-19 is associated with 2-14 days of incubation period and a life-threatening respiratory illness especially for those elderly smoker patients with simultaneous comorbidities [2] [3] .
It seems that the nal solution to stop the pandemic would be a safe and e cient vaccine. Many attempts have been made nd a vaccine and one example is the non-replicating adenovirus type-5 (Ad5)vectored COVID-19 vaccine which was introduced by Feng-cai et. al. and has shown appropriate safety and e cacy at the 2nd phase of the clinical trial [4] .
Previous studies have implicated the cross-reactivities between Corona and In uenza viruses on their surface antigens [5][6][7] which are involved in viral invasion and spread and also the overt in ammatory response to virus [8] . There has been also evidences of cross-immunity between corona virus and BCG [9] [10] . Hemagglutinin-esterase is another similar component between corona and in uenza viruses which mediates virus-cell attachment and membrane fusion [11] . So, targeting this shared viral component by anti-in uenza vaccine is expected to prevent from cellular invasion by the corona virus.
In uenza vaccination among clinical staff in Iran has been reported to have a coverage rate of 6% which is higher than national statistics among general population [12] . Furthermore, the higher rate of clinical staffs' exposure to con rmed cases of COVID-19 makes them an appropriate subject for this study.

Methods And Materials
Clinical staff enrolled in this study were requested to ll-up a questionnaire. Subjects were asked regarding their demographics, in uenza vaccination history (during the previous year and before testing positive for Covid-19), medical history of comorbidities (including asthma, diabetes mellitus (DM), hypertension (HTN), cardiovascular diseases (CVD) and immunode ciencies), symptoms they experienced (respiratory and non-respiratory involvement), COVID-19 PCR or Chest CT-scan results and in case of con rmed disease, the severity parameters such as; home care, hospital admission, ICU admission, intubation, oxygen saturation, arterial blood gas results and disease duration. The subjects were segregated into three categories; mild, moderate and severe. Subjects who experienced mild clinical symptoms, those tested positive but were asymptomatic and those individuals con rmed positive through chest CT-scan but were treated at home with conservative measures were considered mild cases.
Severe cases were those who were admitted to the hospital and in the intensive care unit (ICU), respiratory distress with respiratory rate above 30, Oxygenation index (OI) (calculated by partial pressure of oxygen (O 2 ) divided by fraction of inspired oxygen (FiO 2 ) less than 300 mmHg and those with oxygen saturation less than 93%. Those subjects whose clinical manifestation fall between these spectrums were considered moderate cases. This study was approved by the research committee of the Iran University of Medical Sciences (IUMS) with a code number: IR. IUMS. REC.1399.414.

Analysis:
Statistics of quantitative data were presented by means and variances while qualitative data were reported by their frequencies. Chi-square test was used to assess dependence between categorical variables. Parametric data were compared using student T-test and Mann-Whitney U Test. P-value equal or less than 0.05 was considered statistically signi cant. Analyzes were performed using IBM SPSS version 22.

Results
Of the 510-healthcare staff that participated in the study, 33 were infected by SARS-COV2 accounting to a prevalence rate of 6.47 % among our hospital staff while 132 (25.9%) of the participants have history of in uenza vaccination. 176 were males and 334 were females and the mean age of the participants was 28.94 with an SD deviation of 5.87 years. Furthermore, the subjects of the study were equal in terms of the basic variables such as age and sex.
Individuals in vaccinated and unvaccinated groups were not statistically signi cant in terms of frequency on gender categories (P = 0.108) and also were not signi cantly different in terms of age (P = 0.441 =).
The prevalence and duration of comorbidities such as diabetes mellitus (DM), hypertension (HTN), asthma, cerebrovascular diseases (CVD) and immunode ciencies were not statistically signi cant (Pvalue > 0.05) [ Table 1, Table 2] between vaccinated and unvaccinated participants and so the samples in two groups were equal in their baseline characteristics.     Table 5]. Results of the 114 PCRs or chest CT-scans showed that 33 of the participants were positive of Covid-19. The most prevalent manifestations of the disease were musculoskeletal pain, fever and cough. Disease duration was signi cantly higher on participants with history of in uenza vaccination (P-value = 0.020) [ Table 5]. One participant positive with Covid-19 without any history of in uenza vaccine has been admitted to a general ward while 2 of the participants infected with the virus with previous u vaccination were admitted to the ICU and were intubated. There was no signi cant difference noted on the oxygen saturation level (SaO 2 ) between the vaccinated and unvaccinated participants (P-value = 0.149) [ Table 5]. Furthermore, we observed no signi cant difference in severity of the disease among asthmatics and non-asthmatic patients (P-value = 1.000, Fischer exact test).

Discussion
This study found no signi cant correlation between in uenza vaccination prior to the pandemic to the rate of infectivity and the severity of the disease caused by COVID-19.
Nucleocapsid protein (N protein) and spike protein (S protein) are two major surface components of Corona virus which are involved in its pathogenesis [8]. Both proteins are also present on the surface of in uenza virus [13] [14] . Since N protein is associated with viral assembly and budding and S protein is involved in in ammatory reactions by inducing the host immune response, in uenza vaccination was expected to decrease both proliferation and the in ammatory response caused by corona virus.

Hemagglutinin-esterase (HEs) is another shared viral capsid component of in uenza and corona viruses
which mediated host cell membrane invasion and fusion [11] .
Regardless of the mentioned shared antigenic components between corona virus and in uenza, the novel SARS-COV2 (COVID-19) virus is not identical in its antigenic components with conventional corona virus which has made it more pathogenic and consistent with a more severe life-threatening disease. S glycoprotein on the surface of SARS-COV2 has 12.8 % antigenic variety with SARS-COV, with this in mind that the spike protein accounts for immune response against the virus [15] . There are also additional structural loops on receptor binding (S1) and fusion (S2) domains of the spike protein on SARS-COV2 [16] .
Our results suggest that previous in uenza vaccination has no correlation with Covid-19 infection nor the severity of novel SARS-COV2 (COVID-19) disease regardless of the previously reported antigenic similarity between in uenza and corona viruses could be explained by the antigenic variety of novel 2019 corona virus from its conventional form which accounts for its higher pathogenicity and severity.
The equality of the baseline characteristics such as demographic parameters and the presence of comorbidities among the vaccinated and unvaccinated participants were ensured and the confounding biases were addressed.
Also, results of the study indicated that there is no signi cant difference in the severity of the disease between asthmatics and non-asthmatics which is compatible with previous studies [17] and this could be explained by the fact that eosinophils have a prominent role in immune response against viral illnesses such as in uenza virus as a determinant of the severity [17] .

Conclusion
In uenza vaccination is a not recommended for the prevention of COVID-19. It is neither effective in reducing the rate of infection nor decreases the severity of the 2019 novel SARS-COV2 disease.

Declarations
Ethics approval and consent to participate:

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Con icts of interest/Competing interests
Authors declare no nancial or non-nancial con ict of interest in subject matters of this study. This study did not receive any speci c grant from any companies, funding agencies in the public, commercial, or not-for-pro t sectors.