Simple models to include influenza vaccination history when evaluating the effect of influenza vaccination

Abstract

Background Most reports of influenza vaccine effectiveness consider current-season vaccination only. Aim We evaluated a method to estimate the effect of influenza vaccinations (EIV) considering vaccination history. Methods We used a test-negative design with well-documented vaccination history to evaluate the average EIV over eight influenza seasons (2011/12–2018/19; n = 10,356). Modifying effect was considered as difference in effects of vaccination in current and previous seasons and current-season vaccination only. We also explored differences between current-season estimates excluding from the reference category people vaccinated in any of the five previous seasons and estimates without this exclusion or only for one or three previous seasons. Results The EIV was 50%, 45% and 38% in people vaccinated in the current season who had previously received none, one to two and three to five doses, respectively, and it was 30% and 43% for one to two and three to five prior doses only. Vaccination in at least three previous seasons reduced the effect of current-season vaccination by 12 percentage points overall, 31 among outpatients, 22 in 9–65 year-olds, and 23 against influenza B. Including people vaccinated in previous seasons only in the unvaccinated category underestimated EIV by 9 percentage points on average (31% vs 40%). Estimates considering vaccination of three or five previous seasons were similar. Conclusions Vaccine effectiveness studies should consider influenza vaccination in previous seasons, as it can retain effect and is often an effect modifier. Vaccination status in three categories (current season, previous seasons only, unvaccinated) reflects the whole EIV.

Does repeated influenza vaccination attenuate effectiveness? A systematic review and meta-analysis

“…83 Influenza infection was identified by RT-PCR in 79 (95%) studies and by a rapid diagnostic test in four (5%) studies. 89,[95][96][97] 43 (51%) of 83 studies were done in outpatient settings, 19 (23%) in inpatient settings, 42,43,45,46,[52][53][54][55]60,71,76,77,84,85,87,[91][92][93][94] 13 (16%) in outpatient and inpatient settings, 44,[47][48][49][50][51]66,[68][69][70]80,89,106 and eight (10%) in community settings. 8,79,88,105,107,108,111,113 Influenza vaccination was confirmed by medical record or registry in 41 (49%) studies, 13,22,[42][43][44][45][46]…”

Effectiveness of influenza vaccination in preventing influenza in primary care, Navarre, Spain, 2021/22

“…Adjusted models included sex, age group (9–24, 25–44, 45–64, 65–84 and ≥ 85 years), major chronic conditions, and month of swabbing. Although we performed the classical analysis including only current season vaccination, we considered as final IVE estimates those from models that included vaccination status in three previous seasons, using individuals unvaccinated in all seasons as reference category [ 6 ]. IVE was estimated as a percentage: (1–OR) x 100.…”

“…Moderate or low IVE is frequently observed in seasons with influenza A(H3N2) dominance [ 6 , 8 ]; furthermore, the very low influenza circulation in the 2020/21 season limited the information that supported the selection of the 2021/22 season vaccine composition [ 9 ].…”

“…Vaccines received in previous seasons may retain some preventive effect and modify the effect of the current season vaccine [ 6 , 8 , 10 ]. From the individual perspective, the total preventive benefit is the combined result of vaccinations received in the current and previous seasons.…”

Chronic obstructive pulmonary disease and influenza vaccination effect in preventing outpatient and inpatient influenza cases

“…When differences among category estimates were not statistically significant, these categories were aggregated to simplify the presentation of results as follows: current-season vaccination regardless of prior doses, vaccination in prior seasons but not in the current one, and neither current-season vaccination nor prior doses as the reference category 17 . The rationale for this categorization has been described elsewhere 29 .…”