Objectives:
Epidemiological studies on the impact of fish consumption on coronary heart disease (CHD) incidence have shown inconsistent results. Therefore, this review article has been conducted.

Objectives:
What is the prevalence of underlying disease in died people with COVID-19?  

Study design:
This review article included 32 articles.

Results and conclusions:   
The investigators found the most prevalent comorbidities among COVID-19 were hypertension, diabetes, cardiovascular disease, liver disease, lung disease, malignancy, cerebrovascular disease, COPD and asthma.

Objectives:
What is the incubation period of SARS-CoV-2 (COVID-19)?  

Study design:
This review article included 18 studies, representing 22,595 participants.

Results and conclusions:   
The investigators found pooled average incubation period of SARS-CoV-2 was 5.7 days [95% CI = 5.1 to 6.4].

Objectives:
No systematic review or meta-analysis has yet been conducted to examine the impact of the pandemic on the prevalence of sleep problems among the general population, healthcare workers or COVID-19 patients. Therefore, this review article has been conducted.

What is the prevalence of sleep problems among the general population, healthcare workers or COVID-19 patients?  

Objectives:

Objectives:
Tocilizumab (TCZ) is an anti-interleukin-6 antibody that has been used for the treatment of severe coronavirus disease 2019 (COVID-19). However, concrete evidence of its benefit in reducing mortality in severe COVID-19 is lacking. Therefore, this review article has been conducted.

Does the addition of tocilizumab to the standard of care reduce mortality in severe COVID-19 patients?  

Objectives:
Diabetes mellitus is considered a common comorbidity of COVID-19, which has a wide spectrum of clinical manifestations ranging from asymptomatic infection to severe respiratory symptoms and even death. However, the impact of COVID-19 on blood glucose has not been fully understood. Therefore, this review article has been conducted.

Does COVID-19 infection increase blood glucose and HbA1c levels?  

Objectives:
Probiotics are being used increasingly in pregnant women, whereas the efficiency on pregnancy outcomes is yet lacking. Therefore, this review article has been conducted.

Objectives:
Heated debates have been on-going about tea consumption and the incidence of cancer, especially in head and neck cancer types. Therefore, this review article (meta-analysis) has been conducted.

Does habitual tea consumption reduce risk of nasopharyngeal cancer?

Study design:
This review article included 6 articles.

Objectives:
A lower conversion vaccination rate and a more rapid decline in antibody titers over time in dialysis patients raise concerns about the effectiveness of pneumococcal vaccination (PV) in this population, which has not been systematically reviewed. Therefore, this review article has been conducted.