At the University of New Mexico Hospital in Albuquerque, meanwhile, Melissa Martinez runs a drive-through clinic providing 10,000 influenza vaccines each year for a community made up largely of Black and Hispanic residents. It’s open to all comers, and they all get the standard vaccine.

These different approaches to preventing influenza, a serious threat to the young and old even with the coronavirus that causes covid-19 on the scene, reflect how federal health officials haven’t taken a clear position on whether the high-dose flu vaccine — on the market since 2010 — is the best choice for older people. Another factor is cost. While Medicare reimburses both vaccines, the high-dose shot is three times more expensive, and carrying both vaccines for different populations requires additional staffing and logistics.

“We’ve focused on giving the standard-dose vaccine, trying to get as many people vaccinated as possible,” Martinez said. Her clinic will keep doing so, she added, until the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices decides whether to preferentially recommend the enhanced vaccines.

The CDC historically has been reluctant to pick winners among manufacturers’ competing products to prevent or treat disease. It recommended all three licensed coronavirus vaccines after establishing that each met its disease-fighting goals.

In a given year, most influenza vaccines are not very effective. Drug companies vying for market share aren’t generally motivated to compare them, since they might lose out. And federal officials generally don’t fund such studies, so they are left to rely on research offered by the companies.

Meanwhile, older minority patients, especially Black seniors, are getting the short end of the stick, say some advocates for eliminating racial disparities in health care. Blacks are about 20 percent less likely than Whites to get flu shots, although they are at higher risk of severe flu. Even those who get the vaccine are about 30 percent less likely to get the high-dose version.

“Since you have an increased risk of diabetes and heart disease in the African American community, it inherently disadvantages this population to give them the standard-dose vaccine,” said Keith Ferdinand, a cardiologist and professor of medicine at Tulane University. While the data on the high-dose vaccines is not ironclad, “any tool we have in our toolbox to reduce ethnic/racial disparities should be embraced,” he said.

A CDC work group has been investigating the issue since before the pandemic, with plenty of pandemic-caused delays. On Feb. 23, committee members heard evidence that the high-dose flu vaccine and two other “enhanced” vaccines — one containing an immune-boosting substance, the other a recombinant protein — were better than low-dose vaccine produced in hens’ eggs, the standard product for the past 80 years.

The committee may vote at its next meeting, probably in June, on the matter. At February’s meeting, one CDC official estimated that switching to those vaccines for seniors could reduce influenza-related hospitalizations by thousands a year.

But even a June vote would be too late to affect vaccinations before the fall flu season. Pharmacies and health systems have already ordered next season’s vaccine, and drug companies are committing their facilities now to meet the demand, said Michael Greenberg, a Sanofi vice president.

Sanofi stands to gain from expanded use of its more expensive high-dose vaccine (it also produces a standard-dose version). Germany, Canada and other countries provide the vaccine free to residents of long-term care facilities, but not to all seniors. In the United States, an estimated 75 percent of elders who are vaccinated receive an enhanced shot.

But the remainder, who get the standard vaccine, are disproportionately members of ethnic and racial minorities, according to a study of the 2015-2016 flu season.

The racial and ethnic gaps are wider in doctors’ offices than pharmacies, which are more likely to stock both high-dose and standard vaccines, said Salaheddin Mahmud, director of the Vaccine and Drug Evaluation Centre at the University of Manitoba and first author in the report, which was funded by Sanofi.

In a more recent, as-yet-unpublished study that included data through 2018, Mahmud found that Southerners were less likely to get the high-dose vaccine than other Americans, and high-dose vaccine appeared to be less available in communities where more than 20 percent of the population were minorities.

A decision to give all seniors the enhanced shots isn’t as simple as it seems. For one thing, the CDC’s advisory committee, known as ACIP, hesitates to promote one vaccine over another, afraid that doing so could lead non-touted producers to exit the market and cause vaccine shortages.

In 2017, the advisory committee recommended GlaxoSmithKline’s Shingrix shot over an older shingles vaccine, but even then the committee vote was only 8 to 7 despite clear evidence of Shingrix’s superiority, says Kelly Moore, a professor of health policy at Vanderbilt University who led the Tennessee Department of Health’s immunization program at the time. As committee members feared, Merck took the older vaccine, Zostavax, off the market in the United States, and for years there were shortages of Shingrix.

Each February, flu vaccine formulas are based on scientific modeling of which strains of the mutating virus will be present the following fall and winter. A mismatch can render the best vaccines nearly powerless to prevent infection, although any vaccine protects somewhat against severe illness. This year’s flu vaccine did almost nothing to prevent infection.

Amid all this uncertainty, many health systems and clinics don’t bother buying high-dose or other enhanced vaccines. It’s complicated to store and administer them separately, physicians say, and patients often get vaccinated at a pharmacy rather than by their doctor. While Medicare will reimburse vaccination with any formula, clinics that end up with leftovers usually have to throw them out — a costlier proposition when the vaccines were more expensive to begin with, said L.J. Tan, chief strategy officer for Immunize.org, a group that promotes vaccination.

For this reason, financially strapped community clinics “try very hard not to waste vaccine doses” and may opt for the simpler, cheaper solution, said Julia Skapik, a clinician in Virginia who is also chief medical information officer at the National Association of Community Health Centers.

The best comparative study indicates it’s necessary to vaccinate around 1 in about 220 seniors with the high-dose rather than the standard vaccine to prevent a single case of flu.

Since none of the vaccines have great efficacy in older people, the most important thing is to cocoon the vulnerable by “vaccinating the people around them,” said Martinez, a family doctor in Albuquerque.

“At least until the ACIP decides,” she said, “that seems like a better use of our resources.”

This article was produced by Kaiser Health News, a program of the Kaiser Family Foundation, an endowed nonprofit organization that provides information on health issues to the nation.