key: cord-0748153-6k5hz9rr
authors: Harpaz, Rafael
title: COVID-19 vaccine safety monitoring: Might differential healthcare seeking introduce detection bias into rates of medical events and cause false safety signals?
date: 2021-08-25
journal: Vaccine
DOI: 10.1016/j.vaccine.2021.06.002
sha: 9819e53aebdd90b28000dd3957cc685477533f28
doc_id: 748153
cord_uid: 6k5hz9rr

nan

Diminished background rates of medical events during the pandemic notwithstanding, once persons became vaccinated, it follows that their healthcare behavior would adjust to their diminished risks and fears. They would increasingly seek care, and detection of medical events would increase to betterapproximate true rates. As a result of these considerations, rates of medical event following vaccination would appear to be increased following vaccination as compared to background rates, whether those background rates were derived in self-controlled analyses (ie, from pre-vaccination person-time) or in conventional cohort analyses (from suitable unvaccinated controls). Given the striking decline in healthcare encounters noted above, the magnitude of this detection bias could be considerable, at times falsely-signaling safety concerns.

Of note, since most individuals are aware that COVID-19 provides protection against recurrent SARS-CoV-2 infection for some duration of time, those experiencing COVID-19 might also be expected to adjust their behavior and seek care for subsequent medical events as compared to their pre-COVID-19 disease behavior. In this context, the possible effect might be false evidence of long-term COVID-19 disease complications. 5 Solutions to these vexing problems seem difficult. During the pandemic, healthcare seeking appears to have been deferred for most medical events, although the magnitude of the deferral probably varied by the nature of the event and its perceived seriousness. One partial fix might therefore be to normalize this effect by characterizing the burden of the medical event in question as a proportion of all acute medical events (eg, percentage of total department visits for any acute medical events) rather than to characterize them as rates (incidence). 6 

The critical role of background rates of possible adverse events in the assessment of COVID-19 vaccine safety. Vaccine

National Syndromic Surveillance Program Community of Practice. Impact of the COVID-19 Pandemic on Emergency Department Visits -United States

Admissions to Veterans Affairs Hospitals for Emergency Conditions During the COVID-19 Pandemic

6-month neurological and psychiatric outcomes in 236 379 survivors of COVID-19: a retrospective cohort study using electronic health records

Psychological stress as a trigger for herpes zoster: might the conventional wisdom be wrong? Clin Infect Dis