04/01/2026
I get questions about the shingles vaccine, so here's info from the studies: Only 3.5 out of 100 unvaccinated people in this age group developed shingles over roughly three years. That means 96.5 out of 100 would not have gotten shingles anyway, with or without the vaccine.
“97% effective” means the vaccine reduced the rate among those who would have gotten shingles. It does not mean 97 in 100 vaccinated people are protected from something that would otherwise have happened to them.
The absolute benefit, the actual reduction in cases attributable to vaccination, was about 3.4 cases prevented per 100 people vaccinated over three years. That translates to a “number needed to treat” (NNT) of approximately 30 people you need to vaccinate in this age group to prevent one case of shingles over a three-year period.
In the trials, 78 to 84 percent of vaccinated people reported at least one reaction within 7 days, compared with about 30 percent in the placebo group. Most were mild: sore arm, tiredness, headache. But a meaningful proportion were severe enough to disrupt daily life. This is measured as “grade 3” reactions — fever over 39°C, muscle pain that prevents normal activity, and injection-site pain at rest.
The “number needed to harm” (NNH) for a grade 3 reaction, meaning one serious enough to stop you doing normal things for a day or two, was:
• Ages 50–69: approximately 1 in 11 vaccinated people
• Ages 70+: approximately 1 in 25 vaccinated people
All of the clinical evidence for Shingrix, every pivotal trial, every extension study, every long-term follow-up analysis, was funded by GlaxoSmithKline, the vaccine’s manufacturer. Several named authors on the key publications were GSK employees at the time. Medical writing for the main publications was paid for by GSK. The decision about when to submit results for publication was made by GSK.
For the full description, go here:
The headline number is 97% effective. The number that actually matters to you is closer to 3%. Both are true. Here's what's going on — and why the distinction matters.