Objectives:
There are several guidelines that recommend pneumococcal vaccination (PPSV23 and/or PCV13) in adults with a history of cardiovascular disease (established heart failure, coronary disease, cerebrovascular disease) or at a very-high risk of cardiovascular disease. However, there is no Randomized Controlled Trial (RCT) systematic review that evaluates the impact of vaccination on all-cause mortality compared to no vaccination in this particular population. Therefore, this review article has been conducted.

Male, aged over 65, smoking patients have a greater risk of COVID-19

Objectives:
What are the risk factors, clinical manifestations and laboratory examinations for the progression of COVID-19?

Study design:
This review article included 13 studies with a total number of 3,027 patients with SARS-CoV-2 infection (COVID-19 infection).

All of the selected studies were published in 2020 with different sample patient sizes that ranged from 27 to 1,099 patients.

Objectives:
Is an elevated IL-6 level associated with severe coronavirus disease-2019 (COVID-19)?

Study design:
This review article included 9 studies.

Results and conclusions:
The investigators found patients with severe COVID-19 had a significantly higher serum IL-6 levels compared to non-severe patients [MD = 38.6 pg/mL, 95% CI = 24.3 to 52.9 pg/mL, p 0.001, I2 = 98.5%].

Objectives:
Previous studies did not draw a consistent conclusion about the effects of vitamin K combined with vitamin D on human skeletal quality. Therefore, this review article has been conducted.

Does vitamin K combined with vitamin D supplementation increase bone mineral density (BMD)?

Objectives:
There are sparse data in literature regarding conjunctivitis incidence in COVID-19 and its relationship with disease severity. Therefore, this review article has been conducted.

Objectives:
Previous meta-analyses concluded that there was insufficient evidence to determine the effect of N95 respirators. Therefore, this review article has been conducted.

Is the use of N95 respirators compared with surgical masks associated with a lower risk of laboratory-confirmed influenza?

Study design:
This review article included a total of 6 RCTs involving 9,171 participants.

Objectives:
Is there an association between total meat, red meat, processed meat, poultry and fish intake and risk of type 2 diabetes (T2D)?

Study design:
This review article included 28 prospective cohort studies.

Objectives:
The goals of this meta-analysis is to evaluate the efficacy and safety of current option of therapies for severe acute respiratory syndrome (SARS), Middle Eastern respiratory syndrome (MERS) besides COVID-19, in an attempt to identify promising therapy for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infected patients.

Study design:
This review article included 5 RCTs, 2 prospective cohort studies and 11 retrospective cohort studies with a total of 4,941 patients.

Objectives:
The objectives of this review article is to evaluate the effect of age at administration of the first dose of a measles-containing vaccine (MCV1) on protection against measles and on antibody response after one- and two-dose measles vaccinations.

Scientific studies on measles:
A review article (a collection of scientific studies on a specific topic) of randomized, placebo-controlled double blind clinical trials (RCTs) will answer the following question:
"Do taking dietary supplements make sense?" Yes for a positive conclusion and no for a negative conclusion.

A review article (a collection of scientific studies on a specific topic) of cohort studies or case-control studies will answer the following question:
"Should I change my diet?".