Basic Reproduction Number (R0)
The authors of this article discuss the meaning and misinterpretation of the basic reproduction number (R0) which is a mathematical term that indicates the contagiousness of an infectious disease by identifying the number of secondary cases. Often times, R0 is misinterpreted as a rate but it is rather a dimensionless number. The number can be used to understand various characteristics of the pandemic such as establishing a pathogen in the population, identifying levels of herd immunity and mean age of infection. There are many assumptions that are used in the calculation of the R0 such as availability of data, population homogeneity and similar infection rates in different parts of the population. This, however, is likely not the case in the world as R0 is also dependent on contagiousness, duration of the infection period, and survival. When considering the epidemiologic triangle, the R0 depends on agent/pathogen as described above but also on a number of host and environmental factors such as age, gender, occupation, population density, level of particulate matter, etc. Thus, there is not one R0 for COVID-19 but rather it is variable in different regions and with varied population characteristics. Other factors such as personal hygiene, mask wearing, and additional control measures also affect R0, therefore a uniform R0 is not possible. The authors conclude by stating that R0 is very important to understand and that it is a complex number that can be useful but also has limited applications in the real world due to the variability in agent, host, and environmental factors.
A slew of studies in this literature review have demonstrated that deficiencies in vitamins A, D, and K are associated with an increased risk for severe COVID-19, and that a deficiency in vitamin K specifically is predictive of mortality in those who are hospitalized. The article states that vitamin A, with its immunomodulation effects and maintaining epithelial integrity, can prove crucial in SARS-CoV-2 infection. There have also been many trials and retrospective studies that have supported evidence of the usefulness of vitamin D in COVID-19 patients as low vitamin D levels have been associated with an increase in inflammatory cytokines and a significantly increased risk of pneumonia and viral upper respiratory tract infections. Vitamin D deficiency has also been associated with an increase in thrombotic episodes, which are frequently observed in COVID-19 patients and the deficiency has been found to occur more frequently in patients with obesity and diabetes. Vitamin K is essential for regulating lung health and blood clotting and studies in the review have shown a correlation between vitamin K deficiency and more severe COVID-19 infection. There are many potential nutritional strategies that are being explored to mitigate the severity of COVID-19 infection and although this area remains underexplored, the role of specific vitamins shows great potential.