Effectiveness estimates for enhanced trivalent influenza vaccines in an aged care summer outbreak

Systematic review of influenza vaccine effectiveness against laboratory-confirmed influenza among older adults living in aged care facilities

“…The final study selection included 14 studies, and the study selection process is described in Figure 1 . Of 14 studies evaluated, 12 were case-control or observational studies, 8 , 25–35 and 2 studies were randomized controlled trials (RCTs). 36 , 37 The total number of nursing homes included per study ranged from 1 to 823 nursing homes across the studies.…”

“…In a study by Kunasekaran et al, 25 authors estimated VE for the 2018 and 2019 Southern Hemisphere seasons. In that study, the summer outbreak occurred 10 months after vaccination in 2018, early in 2019, and the reported VEs (for 2018) were 89.8% (95%CI: 18.8%,98.7%) for high-dose (HD-TIV); 72.5% (95%CI: −106.7%, 96.3%) for aTIV and 65.6% (95%CI: −152.3%, 95.3%) for standard TIV.…”

“… 30 The negative VE values were due to more cases among vaccinated individuals than unvaccinated individuals in highly vaccinated aged care populations. 25 , 30–32 In a study by Ng et al, various VEs were reported among residents by vaccination period; an overall adjusted VE of 40.5% (95%CI: −12.2%, 68.5%) was reported in individuals within the post-vaccination period of 15–365 days, while a significant higher VE, 59.3% (95%CI: 18%, 79.8%) was seen in residents who were vaccinated 15–180 days post-vaccination. 26 By subtype, the adjusted VE estimate for A/H3N2 was 57.1% (95%CI: 5.7%, 80.5%), p = .04, and for A/H1N1pdm09, VE was −43.4% and non-significant 26 in 2017.…”

“…In this review, most outbreaks occurred in the influenza season within 1–4 months post-vaccination, and there were only two studies, where outbreaks were recorded during summer or 8–10 months post-vaccination. 25 , 28 In one study, authors discussed the possibility of wanning immunity due to administration of previous season’s vaccine and importance of timing of vaccination 26 relating to variation of seasonal activity and availability of vaccines. A study by Kunakesaran et al, also discussed the efficacy of vaccine and vaccine waning in nursing home residents during the summer outbreak in 2018, nonetheless, VE of TIV reported in that outbreak was moderate and the 2018 seasonal vaccine was found to be protective against infection even after ten-month post-vaccination.…”

“… Gravenstein et al 36 United States Cluster-Randomized Clinical Trial Moderate 2016– 2017 823 facilities (randomized by facilities); Mean age: 83y A/H3N2 Not reported Vaccinated with either adjuvanted TIV or TIV (1:1 ratio) Reduction rate against infection Risk ratio (unadjusted) 17% reduction (0.83; 0.63–1.06); Risk ratio (covariate adjusted) 22% reduction (0.78 (0.60–1.02) The authors stated low vaccine effectiveness of 20% in the season. Kunasekaran et al 25 Australia Observational High 2018–2019 54; Age ≥65y A/H3N2 PCR HD-TIV, adjuvanted TIV and TIV For 2018, VE (HD-TIV): 89.8% (18.8%,98.7%); VE (adjuvanted TIV): 72.5% (−106.7%, 96.3%); VE (TIV): 65.6% (−152.3%, 95.3%) For 2019, VE (aTIV): −102.2% (- 139.8%, 72.7%) Possibility of vaccine mismatch. Cases occurring in vaccinated residents could have been attributed to a less well-matched vaccine against A(H3N2) in the latter part of 2019.…”