Are adverse events in Covid-19 vaccine trials under-reported? By Maryanne Demasi, PhD

Adverse events were almost certainly under-reported. Had they been fully reported, it would have been more difficult to justify the manufacturers’ emergency Use Authorizations, although the authorities would have gone ahead and done so. From Maryanne Demasi at


Phase III controlled trials are considered the ‘gold standard’ for assessing vaccine efficacy and safety in humans. 

These are the trials upon which authorities have assured the public that Covid-19 vaccines are “safe and effective.”

The benefits of the vaccines in reducing disease severity and hospitalisations are well-known, but what do we know about the adverse events? 

Data on adverse events is vital for effective decision-making by regulators, policy makers, doctors, and patients. 

But there are serious concerns about publication bias or selective omission of data, whereby adverse events are less likely to be published than positive results. 

A systematic review in PLOS journal analysed 28 studies and found that adverse events were less likely to appear in published journal articles than unpublished studies (e.g. industry-held data).

Experts now suggest that the pivotal Covid-19 vaccine trials may have under-reported adverse events in several ways.

Virtual monitoring with digital apps

In the Pfizer and AstraZeneca vaccine trials, participants were given digital apps to record adverse events remotely – a more convenient, time efficient and cost-effective way of gathering patient data. 

A major problem however, is that the pre-determined options on the digital apps have a narrow focus on particular adverse events.

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