Abstract: The rollout of booster doses of COVID-19 vaccines to the general population is controversial. The ratio of vaccine risk to benefits likely has swung more towards risk than during the original randomized trials, due to dose-dependent adverse events and to fixation of immune responses on a variant no longer circulating, yet the evidence underpinning mass use of boosters is weaker than was the evidence for the original vaccine rollout.
In light of an unsatisfactory risk-evidence situation, aggregate weekly data on excess mortality in New Zealand are used here to study the impacts of rolling out booster doses. Instrumental variables estimates using a plausible source of exogenous variation in the rate of booster dose rollout indicate 16 excess deaths per 100,000 booster doses, totalling over 400 excess deaths from New Zealand's booster rollout to date. The value of statistical life of these excess deaths is over $1.6 billion. The age groups most likely to use boosters had 7-10 percentage point rises in excess mortality rates as boosters were rolled out while the age group that is mostly too young for boosters saw no rise in excess mortality.