Family spillover effects in cost-effectiveness analyses of vaccines

We evaluated how frequently vaccine cost-effectiveness analyses (CEAs) include family spillover effects, costs or health impacts on family members who care for or about patients, and how their inclusion affects results.

Using the Tufts CEA Registry, we performed a systematic review to identify English-language CEAs published from January 2013 to December 2022 from the societal perspective. We selected CEAs for the four vaccines most evaluated within our search, examined how frequently these CEAs included family spillover effects, and how this inclusion changed CEA results.

Among 268 vaccine CEAs meeting inclusion criteria, the top four vaccines were: human papillomavirus (n = 21), influenza (n = 57), pneumococcal (n = 37), and rotavirus (n = 25). (137 studies, 51 % of total). Of these, 65 (47.4 %) included family spillover effects, predominately time costs (n = 64, 98.5 %). Only four studies (6.2 %) included family spillover health effects. From 30 studies, we created 266 pairs of incremental cost-effectiveness ratios (ICERs), with each pair consisting of one ICER calculated with and then without family spillover effects. We then compared each pair to assess the impact of including family spillover effects on the ICERs. With 29 ICERs (10.9 %), including family spillover changed the result from a positive ICER, with a positive cost and benefit, to cost-saving, with a negative cost and a positive benefit. In 30 cases (11.3 %), ICERs remained cost-saving and in 207 cases (77.8 %) ICERs remained positive, with and without spillover effects. Among these, 206 pairs (99.5 %) showed a mean ICER reduction of 18.8 %, while one pair (0.5 %) increased by 13.3 %.

Approximately half of vaccine CEAs in our sample excluded family spillover effects. When included, most added family spillover costs but rarely family health effects, and generally showed more favorable results. Future vaccine CEAs should appropriately include family spillover effects to reflect vaccines' full value and support evidence-based decision-making.