The Efficacy of SARS-CoV-2 Vaccination in the Elderly: A Systemic Review and Meta-analysis

BACKGROUND: Given the reduced immune response to vaccines in older populations, this study aimed to evaluate the efficacy of COVID-19 vaccinations and its impact on breakthrough infection, hospital admission, and mortality in the elderly. METHODS: We carried out a systemic review and meta-analysis where MEDLINE, Web of Science, EMBASE, ClinicalTrials.gov, and Cochrane Central Register for Controlled Trials were queried to identify relevant literature. We included randomized controlled trials (RCTs), non-randomized trials, prospective, observational cohort, and case-control studies assessing breakthrough infection, hospital admission, and mortality after coronavirus 2 (SARS-CoV-2) vaccination in the elderly ( ≥  60 years old). RESULTS: Overall, 26 studies were included in this meta-analysis. Compared with the unvaccinated group, the vaccinated group showed a decreased risk of SARS-CoV-2 infection after 28-34 (relative risk [RR] = 0.42, 95% confidence interval [CI] 0.37-0.49) and 35-60 days (RR = 0.49, 95% CI 0.37-0.62). There was a step-wise increase in efficacy with additional doses with the two-dose group experiencing decreased risk of breakthrough infection (RR = 0.37, 95% CI 0.32-0.42), hospital admissions (RR = 0.25, 95% CI 0.14-0.45), disease severity (RR = 0.38, 95% CI 0.20-0.70), and mortality (RR = 0.21, 95% CI 0.14-0.32) compared with those receiving one or no doses. Similarly three-dose and four-dose vaccine groups also showed a decreased risk of breakthrough infection (3-dose: RR = 0.14, 95% CI 0.10-0.20; 4-dose RR = 0.46, 95% CI 0.4-0.53), hospital admissions (3-dose: RR = 0.11, 95% CI 0.07-0.17; 4-dose: RR = 0.42, 95% CI 0.32-0.55), and all-cause mortality (3-dose: RR = 0.10, 95% CI 0.02-0.48; 4-dose: RR = 0.48, 95% CI 0.28-0.84) Subgroup analysis found that protection against mortality for vaccinated vs. unvaccinated groups was similar by age (60-79 years: RR = 0.59; 95% CI, 0.47-0.74;  ≥  80 years: RR = 0.76; 95% CI, 0.59-0.98) and gender (female: RR = 0.66; 95% CI, 0.50-0.87, male: (RR = 0.58; 95% CI, 0.44-0.76), and comorbid cardiovascular disease (CVD) (RR = 0.69; 95% CI, 0.52-0.92) or diabetes (DM) (RR = 0.59; 95% CI, 0.39-0.89. CONCLUSIONS: Our pooled results showed that SARS-CoV-2 vaccines administered to the elderly is effective in preventing prevent breakthrough infection, hospitalization, severity, and death. What's more, increasing number of vaccine doses is becoming increasingly effective.