Among adults who had a personal doctor and health coverage in 2023, 54.9% of those earning $200,000 or more got a flu shot. Among those earning under $15,000, the rate was 39.1%. Same access, same coverage, 15.8 percentage points apart.

That gap is larger than the entire flu vaccination rate for uninsured adults without a doctor in some income brackets. And it has been growing.

A Gap That Widened While Access Expanded

In 2014, the income gradient in flu vaccination was already visible but relatively contained. Adults earning under $15,000 had a vaccination rate of 33.1%, compared to 42.2% for those earning $50,000 or more, a spread of 9.1 percentage points. By 2016, the gap had actually narrowed slightly, to 7.3 points (34.1% vs. 41.4%). In 2017, it sat at 6.5 points (36.4% vs. 42.9%).

Then the 2023 data arrives with a different income classification that separates out the top earners, and the picture changes sharply. With the $200,000-plus group now visible as its own tier, the gap between the lowest and highest income adults with a personal doctor reaches 15.8 percentage points. That's not a measurement artifact. It reflects what happens when you can actually see the top of the income distribution: the gradient is steeper than the older, compressed income categories suggested.

For a vaccine that is free or near-free for most insured adults, a 15.8-point gap tied to income is a significant finding. Flu vaccination is not a high-cost, high-complexity intervention. It requires a brief clinical encounter, no prescription, and no follow-up. If income predicts uptake this reliably even among people who have a doctor and coverage, the barrier is something other than cost or access.

Having a Doctor Helps, But Doesn't Equalize

The comparison between adults with and without a personal doctor is stark. In 2023, adults without a personal doctor had vaccination rates ranging from 18.4% (the $25,000-$35,000 group) to 33.1% (the $200,000-plus group), all substantially below their counterparts who had a doctor. For the lowest income group, having a personal doctor was associated with a 17.1-point difference in vaccination rates: 39.1% with a doctor versus 22.0% without one.

That finding confirms what most analysts assume: the healthcare relationship matters enormously for preventive care delivery. But it also reveals the limit of that relationship as an equalizer. Even after controlling for doctor access, the income gradient doesn't disappear. Adults earning $200,000-plus with a personal doctor were vaccinated at 54.9%, while adults earning under $15,000 with a personal doctor were vaccinated at 39.1%. The doctor helps everyone, but it helps higher-income patients more.

This has a concrete implication for how we measure progress on health equity. Expanding access to primary care is necessary, but it is not sufficient to close income-based gaps in preventive care. A policy that achieves universal primary care coverage would still leave a substantial vaccination gap intact, based on the 2023 data.

The Gradient Holds Across a Decade

The 2024 data, which compares adults earning under $15,000 (36.7%) to those earning $100,000-$200,000 (45.4%), shows an 8.7-point gap. That's consistent with the pre-2023 range, and the $200,000-plus tier isn't separately available for 2024 in this analysis. If it were, the gap would likely be wider.

Across every year in this dataset, the direction is the same: higher income, higher vaccination rate. The magnitude shifts depending on how income is categorized and which population is examined, but the gradient never reverses, never flattens to zero, and never disappears even among the most healthcare-connected adults.

Given that the income gradient persists at 15.8 percentage points among adults who already have a doctor and coverage, the question that the data keeps raising is what, specifically, is being delivered differently in high-income clinical encounters that makes a flu shot more likely to happen.