I asked ChatGPT o3 what the chances are of getting a serious infection if you take biological medications such as Enbrel, Humira, or Remicade. It gave a table with links to a lot of research and said as a takeaway: Serious infection: 3–6 % of patients per year (disease, age, and steroids matter more than the brand of TNF-blocker).
I then asked: How much statistical independence is there from year to year on the 3% to 6% number? In other words, if somebody has a 5% chance of getting a serious infection caused by this in one year, is it fair to that over the course of 10 years, the chances are 1 - (1-5%)^10?
It gave a long answer, which I asked it to restate in a way that could be copied here. It said:
How risky are serious infections on Remicade (and other anti-TNF drugs)?
Short version:
• The headline “5 % per year” is a rate, not a simple yearly coin-flip.
• Real-world data show roughly 1 in 5 patients will have one or more serious infections over 10 years—about half what the naïve 40 % math suggests.
Why the raw 5 % × 10 years = 40 % math overstates things
- Risk isn’t flat. It’s highest in the first 3–6 months, then drops once the disease is under control.
- Events aren’t independent. A person who’s already had one infection is 2–3× likelier to get another, skewing averages.
- Many patients stop or switch the drug. About 30 % drop off anti-TNFs within 5 years, so their later years don’t count toward risk on that drug.
- Rheumatoid arthritis: ~20-25 % hit one serious infection by year 10.
- Ankylosing spondylitis / axial SpA: ~10-15 % over 10 years (younger, fewer steroids).
- Crohn’s disease: similar ballpark, but steroids triple the risk.
> “For someone without major lung disease or chronic steroids, anti-TNF therapy carries about a one-in-five chance of at least one hospital-level infection over the next decade. The risk is front-loaded in the first six months and rises more slowly after that.”
Ways to shrink that risk:
- Screen for latent TB & hepatitis before starting.
- Keep vaccines current (flu, pneumonia, shingles, COVID, etc.).
- Taper steroids as quickly as possible.
- Treat fevers aggressively—don’t ‘wait and see.’
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It provided links to the following papers supporting its conclusion:
https://pmc.ncbi.nlm.nih.gov/articles/PMC2435418/
https://pubmed.ncbi.nlm.nih.gov/23365147/
https://pubmed.ncbi.nlm.nih.gov/25125593/
https://pmc.ncbi.nlm.nih.gov/articles/PMC3438468/