Patients in nursing homes that provided a high–dose flu vaccine were significantly less likely than residents in standard–dose homes to go to the hospital during flu season, according to a new study.

The fact that vaccines typically don’t work as well in older people presents a challenge to influenza vaccine makers, particularly because the illness often results in serious respiratory infections in frail patients such as elderly nursing home residents.

A large, randomized clinical trial tested whether a flu vaccine with four times the antigen of a standard vaccine could reduce the risk of hospitalization among those especially vulnerable seniors. The results, published in the Lancet Respiratory Medicine journal, reports that it did so significantly.

Lead author Dr. Stefan Gravenstein, a professor at both the Warren Alpert Medical School and the School of Public Health at Brown University, said that while a prior study showed that older individuals could respond better to the high–dose vaccine, that study focused on relatively healthy older adults.

The study compared hospitalization rates among more than 38,000 residents of 823 nursing homes in 38 states during the 2013–14 flu season based on Medicare claims data. Just under half the homes, 409 to be exact, administered the high–dose vaccine while the other 414 provided a standard dose. In the end, the hospitalization rate for respiratory illnesses among high–dose patients was 3.4 percent compared to 3.8 percent among standard–dose patients over the six months after vaccination. Statistical analysis revealed that the relative risk of hospitalization for respiratory illness was 12.7 percent lower for the high–dose group.

Moreover, Gravenstein and his co–authors found that the rate of hospitalization for any reason, respiratory or otherwise, was significantly lower in the high–dose group as well. For every 69 people given the high–dose vaccine vs. the standard–dose vaccine, one more person stayed out of the hospital during the flu season.

“Respiratory illness as the primary reason for hospitalization accounted for only about a third of the reduction in hospitalization that we measured,” said Gravenstein, who is also affiliated with the Providence Veterans Affairs Medical Center and is an adjunct professor of medicine at Case Western Reserve University. For many patients, the vaccine appeared to help prevent hospitalization for other problems also, including cardiovascular symptoms.

Gravenstein said the finding of a significant reduction in hospitalizations was particularly notable because the predominant flu strain during the 2013–14 season, A/H1N1pdm, was believed to be less virulent in older people who had spent a long lifetime building up immunity to similar strains.

“That there was differential protection in this context both underlines the potential importance of even low–virulence or less transmissible strains to older populations and the fact that vaccines may afford relevant effectiveness among frail older persons even when A/H1N1 predominates,” the authors wrote.

The study did not find a significant difference in the rate of death. In the paper, the researchers speculate that while the standard–dose vaccine might not have been strong enough to stave off illness entirely, it may still have been sufficient to prevent deaths in combination with hospital care.

But a significant reduction in hospitalizations can still be a benefit, Gravenstein said, even though the high–dose vaccine is more expensive than the standard–dose vaccine. Especially for older, frail patients, he said, reducing otherwise necessary trips to the hospital can maintain a higher quality of life.