2.2. Search strategy
A comprehensive search of the literature was conducted in the following
databases up to May 1, 2020: PubMed, EMBASE, Google Scholar, Science
Direct, Scopus, and Web of Science. All citations were imported into a
bibliographic database (EndNote X8.1; Thomson Reuters) and duplicates
were removed. This search process was handled independently by one
author (AR.M).
The used search string - based on suitable MESH and non-MESH keywords -
were: ((“COVID-19” OR “SARS-CoV-2” OR “Severe Acute Respiratory
Coronavirus 2” OR “coronavirus” OR “virus disease” OR “viral
infection” OR “virus”) AND (“virus titres” OR “titres” OR
“interleukin” OR “IL-6” OR “IL-17” OR “antibody” OR “IgG” OR
“IgA” OR “interferon” OR “INF”) AND (“Synbiotics” OR
“Probiotics” OR “Prebiotics”)). Moreover, bibliographies of all
published reviews and studies were assessed for additional relevant
papers.