Objectives: We aimed to study the effect of seasonal influenza (flu) vaccination on the susceptibility to coronavirus disease 2019 (COVID-19). Methods: A total of 203 healthcare workers of a pandemic centre of Istanbul, Turkey, were included in this retrospective study. According to the presence or absence of flu vaccination, participants were divided into group 1 and group 2. A comparison of the rate of COVID-19 was done between these two groups. Also, the mean age and the sex ratio of females/males were evaluated and compared between these two groups.Results: Group 1 participants (n = 65) were older than participants in group 2 (n = 138) (p < 0.05). Despite of this, interestingly, the COVID-19 infection rate was lower in the 1st group (in comparison to the 2nd group) (p < 0.05). Conclusion:Our study results showed that, even if low, the flu vaccination may have a protective effect on the susceptibility to COVID-19 infection. Using this beneficial adjuvant effect of the vaccine may help us in this unpredictable battle with the COVID-19 pandemic. Further studies are needed to confirm this assumption.

SUMMARY Down syndrome (DS) is one of the main genetic abnormalities of newborns. Therefore, prenatal diagnosis of this syndrome is of paramount importance to the family and the community. The microbiota system is important in early brain development. We tried to study and compare gut microbiota (GM) composition in pregnancies that resulted in DS neonates with pregnancies that resulted in healthy children. The study population consisted of 21 pregnant women having delivered DS newborns (group 1) and 22 pregnant women who had given birth to healthy newborns (group 2). The GM composition was determined and compared between the two groups. There were no significant age and gestational age differences between the two groups (p>0.005 both). Regarding GM analysis, microorganisms of the families Clostridiaceae and Pasteurellaceae were more abundant in the group of women having delivered DS neonates than the group of women having delivered healthy newborns (p<0.05). The results of our pilot study showed that the GM system might have a role in the pathophysiology of DS. The GM changes may be used in the prenatal diagnosis and prevention of this syndrome. Further studies are needed in this field.