Covid Vaccines
Having more vaccine doses leads to more Covid infections, a major study has found.

Researchers at the Cleveland Clinic in Ohio, USA, monitored over 47,500 employees for Covid infections during the first four months of 2024, when the JN.1 virus lineage was dominant. They found that being vaccinated increased infection risk by 46% with two doses, 95% with three doses and 151% with more than three doses, when compared to having zero or one dose

These findings are shown in the table and chart below.

Increased risk of Covid Infections by number of vaccine doses
Number of prior vaccine doses
The study, which is awaiting peer review, confirmed the findings of earlier studies by the same team among the same population. The study in 2022 produced this famous chart, showing cumulative risk from increasing doses. A 2023 follow up found a similar outcome.

Cumulative increases of Covid with increased vaccine doses
The authors have been bolder this time in proposing that the vaccines themselves are responsible for the increased risk - though they blame a possible interaction with natural immunity rather than a direct effect of the drug itself. They write:
Consistent with similar findings in many prior studies, a higher number of prior vaccine doses was associated with a higher risk of COVID-19. The exact reason for this finding is not clear. It is possible that this may be related to the fact that vaccine-induced immunity is weaker and less durable than natural immunity. So, although somewhat protective in the short term, vaccination may increase risk of future infection because the act of vaccination prevents the occurrence of a more immunogenic event. Thus, the short-term protection provided by a COVID-19 vaccine comes with a risk of increased susceptibility to COVID-19 in the future.
This of course supposes that the vaccines gave some protection in the first place, which on this evidence seems doubtful.

A more likely cause would be 'original antigenic sin', where a narrow vaccine-based immune response prevents a broader immune response on encountering the virus, plus the development of tolerance towards the spike protein from repeated dosing.

Overall the study's model found a low protective effect from the recent booster of 23%. However, the authors point out that this was only achieved by adjusting for the number of vaccine doses. In other words, by assuming the number of vaccines shouldn't increase susceptibility and so adjusting the results accordingly, the latest booster seemed to be protective. But if you don't make that adjustment, "the 2023-2024 formulation of the vaccine was not protective against COVID-19", the authors state.

They conclude that "a more nuanced approach to COVID-19 is necessary".
Although some individuals are at high risk of complications from COVID-19, and may benefit from receiving a vaccine frequently, the wisdom of vaccinating everyone with a vaccine of low effectiveness every few months to prevent what is generally a mild or an asymptomatic infection in most healthy persons, needs to be questioned.