One in seven. That is the proportion of people in the MHRA’s own actively recruited surveillance cohort who reported a medically serious adverse reaction following covid vaccination. Over half reported at least one reaction of any kind. The data were collected between 2020 and 2022. They were not published until September 2025, and only then because Cheryl Grainger, through a Freedom of Information (“FoI”) request and subsequent Information Commissioner’s Office (“ICO”) appeal, forced it out.
The paper that eventually appeared, in the journal Drug Safety, was not written as a safety paper. It was written as a description of the digital platform used to collect the data – a methods paper published five months after Dame June Raine left as chief executive, nearly three years after the data were locked. The actual adverse reaction rates are reported but not analysed. The one stratification that could determine whether those rates are real was not performed.
The numbers buried inside it deserved rather more attention.
What the Data Show
The Yellow Card Vaccine Monitor (“YCVM”) was the MHRA’s premium data source. It was one of four pillars of its covid vaccine safety surveillance strategy. Unlike the passive Yellow Card scheme, where people report voluntarily and sporadically, the YCVM actively recruited people and followed them up at set intervals. The MHRA itself described it as a tool to “rapidly detect, confirm, characterise and quantify new risks.”
Of the 30,281 individuals who reported receiving a vaccination, 15,764 (52.1%) reported at least one adverse reaction. 4,134 (13.7%) reported a reaction classified as medically serious under the MedDRA system. This is a regulatory classification that includes events deemed medically significant by an internal MHRA panel and is broader than the lay meaning of “serious,” but not a trivial threshold. It encompasses hospitalisation, disability, life-threatening outcomes and death, but also other events judged clinically important.
However, the 13.7% might include people who volunteered for the monitor becausethey had been injured. The MHRA did not exclude people signing up afterthey had their vaccine.
The key question is how representative this cohort was. Any voluntary cohort, even an actively recruited one, may over-represent people who experienced problems. Other active surveillance systems internationally have reported lower rates, though none has been free of similar methodological limitations. The true rate is unknown – which is precisely the problem.
The YCVM was meant to be designed to quantify risk in a way passive surveillance could not because of reporting bias. However, the key simple analysis to enable interpretation was not done. The question is not whether 13.7% is the true rate of serious harm. The question is why the MHRA did not do the work to find out what the true rate is.
The Cohort It Did Not Analyse
The paper reports 35.6% registered before vaccination and 47.5% after. A further group registered on the same day, but the paper does not quantify it. Even allowing for this, the categories as presented account for only 83.1% of the cohort, leaving 16.9%, over 5,000 people, unclassified. The paper does not explain the gap.
The pre-vaccination and same-day registrants are the key group. They signed up before or at the point of vaccination, not in response to a bad reaction. Their data is substantially less vulnerable to post-event selection bias, which is the main challenge to the headline figures. The criticism that people with bad reactions were more motivated to register does not apply to them. They were already in the system.
The obvious analytical step is to separate these registrants and compare their Adverse Drug Reaction (“ADR”) rates to those who registered afterwards. If the prospective cohort shows substantially lower rates, the selection bias interpretation is supported and you would want to say so. If the rates are similar, the overall figures are validated and you would want to say that too. If the rates are lower, then that is the rate that is of interest and should be published. In any case, the comparison is critical and should have been presented.
The MHRA did not present the comparison. In a 21-page paper with 13 tables, this stratification – the single most important analysis for interpreting the headline findings – does not appear. I have submitted an FoI request for this data.
Hellbound and Down 