Impact of vaccines on Staphylococcus aureus colonization: A systematic review and meta-analysis

Background: Concerns regarding vaccine effects on microbial ecology have led to interest in the non-targeted effects of vaccinations. Objectives: To systematically review the literature related to the impact of vaccines on S. aureus carriage. Methods: We conducted a systematic search of MEDLINE, Scopus and clinical trials.gov for studies that assessed vaccine effects on S. aureus carriage in children and adults using predefined inclusion and exclusion criteria. Generic inverse variance meta-analysis was done using random-effects models. Results: Of 1,686 studies screened, 34 were eligible for inclusion, of which 22 were observational and 12 randomized controlled studies (RCTs). 88.2% (30/34) provided data on pneumococcal conjugate vaccines (PCV), 23.5% on influenza vaccines (8/34), 6% on other vaccines (2/34) and 20.6% on more than one vaccine (7/34). Most studies tested nasopharyngeal specimens (82.3%, 28/34). Among children aged more than 18-24 months, evidence suggested no effect of PCV on S. aureus colonization [2 RCTs, pooled OR 1.09 (95% CI 0.94-1.25), p 0.25; 7 observational studies, pooled OR: 1.02 (95% CI 0.83-1.25), p 0.86]. A transient increase in S. aureus carriage in PCV-vaccinated infants 9-15 months was shown [2 RCTs, pooled OR 1.11 (95% CI 1.00-1.23), p 0.06; 4 observational studies, pooled OR 1.64 (95% CI 1.00-2.68), p 0.05]. A reduction in S. aureus carriage was observed after influenza vaccination [4 observational studies; OR 0.85 (95% CI 0.78-0.94), p 0.0001]. Based on the Grading of Recommendations Assessment, Development and Evaluation, the quality of evidence was considered low for randomized and very low for non-randomized trials. Conclusion: Evidence did not suggest long-term effects of pneumococcal vaccinations on S. aureus nasopharyngeal carriage in children, however transient niche changes may occur in infants. Influenza vaccination was related to decreased rates of S. aureus carriage. Data regarding other vaccines is scarce. Further research and ongoing surveillance are needed to monitor colonization changes.