In � uence of Covid-19 Vaccination Coverage on Case Fatality Rate

Background: Recent evidence suggested that an increase in Covid-19 attack rate is correlated to increased case fatality rate (CFR) Covid-19 disease severity. An increase in the attack rate was suggested to lead to an increase in the viral load a proposed mechanism leading to this association. In this context, we conduct this study to look for the influence of decreasing the number of Covid-19 cases through vaccination on CFR. Material: and methods: We collected data concerning all countries/territories that implement Covid-19 vaccination at least for the last hundred days ending on 3d of April 2021. They were sixteen in number.Descriptive data analysis used included mean value, standard deviation, and graphical presentation by using Stem-Leaf charts and bar charts.Inferential data analyses used included the One-Sample Kolmogorov-Smirnov (K-S) test and general linear model procedure (GLM). Results: : Findings showed that in a highly significant association the mean CFR decreased in countries with > 18 Covid-19 vaccine doses per 100 inhabitants. Conclusion: Vaccination coverage may constitute another factor that determines temporal and spatial variances in CFR.


Introduction
Several factors were suggested to be associated with temporal and spatial variances in the Covid-19 case fatality rate (CFR, the ratio between the number of deaths and number of con rmed cases). Among these factors are comorbidity risk, demographic, socio-economic, and political variables, the age distribution of the community. [1] COVID-19 vaccine has a substantial impact in reducing the incidence, hospitalizations, and deaths, especially among vulnerable individuals with comorbidities and risk factors associated with severe COVID-19. [2] Important measures to monitor countries' vaccination progress include measuring daily or 7-day average decrease in the number of cases, measuring daily or 7-day average decrease in the number of deaths, and measuring the number of con rmed COVID-19 hospital admissions. [3] The positive association between the number of Covid-19 cases /million population inhabitants and CFR was raised in recent literature. [4] , [5] , [6] An increase in attack rate was suggested by these literature to be correlated to disease severity. The suggested hypothesis is that clustering of cases and viral overload lead to increased mortality rate and CFR.
We conduct this study to look for the in uence of decreasing the number of Covid-19 cases through the Covid-19 vaccine on CFR. This will test such a hypothesis in another way since vaccination leads to a decrease in the number of cases.

Material And Methods
We selected all countries / territories that implement Covid-19 vaccination for at least the last hundred days ending on 3d of April 2021. They were sixteen in number. Publically available data derived concerning April 3, 2021, include total doses, vaccine doses / 100 people, total deaths, and accumulative Covid-19 cases. Data regarding total deaths and accumulative Covid-19 cases at the time when that country or territory initiated the Covid-19 vaccination was also derived accordingly. Data is included within the supplementary le.
CFRs were computed as total accumulative deaths divided by accumulative total cases x 100.
Statistical Analysis: The statistical data analysis approaches were used with (SPSS) ver. (21).
1. Descriptive data analysis which included mean value, standard deviation, and Graphical presentation by using Stem-Leaf charts and bar charts.  Table (1) shows the normal distribution function (goodness of t test). It represents a one-sample "Kolmogorov-Smirnov" test procedure comparing the observed cumulative distribution function for studied readings with a speci ed theoretical distribution, which proposed a normal shape (i.e. bell shape).
The results show that the distribution of studied readings regarding CFR marker distribution function in different locations. Since (Pvalue ) is accounted at (P>0.05), this enabled us for applying the convention statistical methods (the parametrical methods).  The severity of COVID-19 has been widely reported to be in uenced by many factors e.g. age, sex ,and underlying comorbidities. [7] In one study vaccination reduced the overall attack rate from 9.0% to 4.6% over 300 days, which constitutes about a 50% reduction . Vaccination markedly reduced adverse outcomes, with non-ICU hospitalizations 63.5%, ICU hospitalizations 65.6%, and deaths decreasing by and 69.3% (95% CrI: 65.5% -73.1%), respectively, across the same period. 2 It is clear that the relative reduction in mortality overcomes the relative reduction in morbidity. This might indicate that the attack rate has a role in mortality per se.
Furthermore, our ndings support the recent evidence of the role of the number of accumulative cases within a certain community in determining CFR. 4,5 ,6 It was suggested that an increase in fatality rate as the number of infected people increases is related to the overwhelming of the healthcare system. 1,[8] This should be tested deeply as far as clusters of Covid- Furthermore, although the number of hospital beds per 1000 people had a negative association with COVID mortality in certain countries including European countries, North America, Mexico, Brazil, Bolivia ,and USA, these ndings were not global. The number of hospital beds per 1000 people did not have such a negative association in many Asian countries (excluding Japan) and in African countries. [11] They displayed comparatively low mortality regardless of their limited bed capacity. The controversy in these ndings might be biased by a high attack rate in some countries which makes these beds insu cient.
On the other hand low attack in other countries probably led to low CFRs regardless of the bed capacity .
This study shed a light on the importance of Covid-19 vaccination coverage in decreasing CFR, an unmeasured factor before. Although vaccines might protect from the severe disease [12] which can decrease the CFR per se, the early detection of such ndings in relatively low vaccination coverage together with the low number of infections that encountered in vaccinated patient. These infections if encountered in vaccinated patients are certainly very low and incomparable to infections in nonvaccinated patients.

Conclusions
Covid-19 vaccination leads to a decrease in CFR in signi cant association possibly due to a decrease in AR .
The attack rate is a possible missed factor explains variances of CFRs among countries or among the same country at different times.

Declarations
• Ethics approval and consent to participate: 'Not applicable • Consent for publication : I certify that this study have not been previously published. The publisher has my permission to publish this study . With the consent, I give the publisher copyright license • Availability of data and materials: We used publically available data. Patients were not involved.
All data generated or analysed during this study are included in this published article [and its supplementary information les].
• Competing interests: There is no con ict of interest to be declared.
• Funding: No funding source to be declared.
• Author contributions : The author wrote the manuscript and provided data, conducted the statistical analyses and reviewed the nal manuscript.