2.3. Study selection criteria, data extraction and quality
assessment
Title, abstract and then full-text of all articles were screened to
select & extract studies that investigated the effect of probiotics on
viral infections (with emphasis on SARS-CoV-2) in English language (all
research types with both human and animal origin). We excluded HIV
papers, due to not being directly related to respiratory viral
infections. Data extraction from primary articles was performed by one
author (AR.M) by using a standardized form. A second author checked the
accuracy of the data extracted (M.P). Data collected from the studies
included authors’ family name, type of study, probiotic strains and
dose, sample size, and overall outcomes. The Cochrane Collaboration
criteria for assessing risk of bias were applied to assess the quality
of the studies included in the review 17.