The Reply

Abstract

We thank Schabas et al for their letter. We agree that COVID vaccination reduces the risk of COVID pneumonia and protects against morbidity, mortality, and long-term disability. We agree that COVID vaccine hesitancy is a substantial problem, diverse factors contribute, and insight into underlying reasons might promote more effective care. The finding from our study is that COVID vaccine hesitancy is associated with an increased risk of a serious traffic crash.1Redelmeier D Wang J Thiruchelvam D COVID vaccine hesitancy and risk of a traffic crash.Am J Med. 2023; 136: 153-162.e5Google Scholar We understand that this finding is controversial.2Clark A. Unvaccinated drivers more likely to be in a car crash, study shows. Globe and Mail. December 22, 2022.Google Scholar The letter suggests that differences in distances driven might confound the association of COVID vaccine hesitancy with traffic risks. However, the study found that traffic crash risks for unvaccinated women exceeded the risks for vaccinated men despite strong general evidence that women drive less than men.3Chipman ML MacGregor CG Smiley AM Lee-Gosselin M Time vs. distance as measures of exposure in driving surveys.Accid Anal Prev. 1992; 24: 679-684Google Scholar An absence of direct data on individual driving distances is a common limitation in traffic science, yet is unlikely to explain the observed increased risks.4Elvik R. Driver mileage and accident involvement: a synthesis of evidence.Accid Anal Prev. 2023; 179106899Google Scholar Another concern is whether differences in occupation might explain traffic risks. Adults living in cities, for example, tend to have different occupations and shorter driving distances than those in rural locations.5Keall MD Frith WJ Characteristics and risks of drivers with low annual distance driven.Traffic Inj Prev. 2006; 7: 248-255Google Scholar However, the study found that the crash risks for unvaccinated adults in cities exceeded the crash risks for vaccinated adults in rural locations. Speculating about occupation, furthermore, neglects the nuance that most traffic crashes are not related to work.6Mitchell RJ Bambach MR Friswell R Work and non-work-related vehicle crashes: the contribution of risky driving practices.Saf Sci. 2014; 68: 65-72Google Scholar A third question is whether differences in vehicles might explain traffic risks. High-income adults, for example, tend to drive more expensive vehicles with more safety features. However, the study found that high-income adults who were unvaccinated had greater risks than low-income adults who were vaccinated. Modern engineering for crash protection is promoted by vehicle manufacturers, yet tends to show modest real-world safety gains for preventing life-threatening crashes.7Masello L Castignani G Sheehan B Murphy F McDonnell K On the road safety benefits of advanced driver assistance systems in different driving contexts.Transp Res Interdiscip Perspect. 2022; 15100670Google Scholar A further criticism is that the COVID vaccine was not widely available in early 2021. COVID vaccination for young children, in particular, was delayed until November 23, 2021 to prioritize seniors, teens, and hot spots.8Government of Ontario. COVID-19 vaccine bookings to open for all children aged five to 11. November 22, 2021. Available at: https://news.ontario.ca/en/release/1001195/covid-19-vaccine-bookings-to-open-for-all-children-aged-five-to-11. Accessed March 7, 2023.Google Scholar The study, however, selected adults over age 18 years, who all had full access as of May 18, 2021 to the vaccine in Ontario.9Government of Ontario. COVID-19 vaccine booking expanding to Ontarians 18+ ahead of schedule. May 17, 2021. Available at: https://news.ontario.ca/en/release/1000143/covid-19-vaccine-booking-expanding-to-ontarians-18-ahead-of-schedule. Accessed March 7, 2023.Google Scholar Therefore, the vaccine was available months ahead of July 31, when analysis of subsequent traffic risks began. Of course, future research is justified with more follow-up and statistical power. Other scattered points in the letter include misquotations or misunderstandings. The study did not use the word “reckless” or punitive legal language. Risk analysis did not assume unvaccinated adults were identical, had “a common psychology,” or experienced equal risks. The conclusion did not advocate “raising car insurance” akin to premiums based on marital status. The manuscript did not use coded language for political messaging.10Carpiano RM Callaghan T DiResta R et al.Confronting the evolution and expansion of anti-vaccine activism in the USA in the COVID-19 era.Lancet. 2023; 401: 967-970Google Scholar The study emphasized traffic risks because road safety requires an accurate understanding.