Ordinary flu vaccine has always worked out for Carolyn Hendrickson, so the 77-year-old was perplexed Monday when her clinic gave her a high-dose version without asking first.

Confusion turned to anger that night as she lay in bed at home in Brooklyn Park. Her muscles ached, her head pounded and her stomach churned.

"I've had the flu shot before and never had a problem," she said. "Why was this different?"

Hendrickson had learned the hard way that a new influenza vaccine, Fluzone High-Dose, is available. The vaccine is loaded with four times the usual virus-fighting antigen, so public health experts believe it will better protect seniors whose immune systems have weakened with age.

But it also causes a slightly higher rate of side effects, mostly short-term aches and flu-like symptoms.

Hendrickson was back to full strength Friday. But in hindsight, she wonders if she would have taken the high-dose version if her clinic had offered her a choice.

Fluzone High-Dose was first offered midway through last flu season. Manufacturer Sanofi Pasteur estimates that 10 percent of seniors who were vaccinated last season received the high-dose version.

Studies have shown that the larger dose stimulates the immune system to respond more aggressively against influenza. But research hasn't yet proven that the vaccine is more effective for seniors. Answers to that question are expected in 2014 or 2015, according to the U.S. Centers for Disease Control and Prevention (CDC). The federal agency has taken no position yet on whether seniors should opt for this type of vaccine.

For now, it is "between the provider and patient" to decide when to use Fluzone High-Dose -- assuming a clinic has any in stock, said Kristen Ehresmann, who directs immunization programs for the Minnesota Department of Health. Hendrickson complained to her as well. Ehresmann replied that it wasn't unethical or illegal for her clinic to provide the high-dose version without offering a choice.

"Some clinics may have decided to offer high-dose flu vaccine to their senior population," she said. "That would be reasonable. When physicians prescribe a medication, they don't necessarily say, 'There are six antidepressants on the market; which one would you like to take?' The providers use their judgment and prescribe a medication. The same could be said for flu vaccine."

A clear need

The need for better vaccines is evident from the fact that influenza contributes to 3,000 to 49,000 U.S. deaths each year, according to the CDC. Most victims are 65 or older.

Further proof came this fall from the University of Minnesota's Dr. Michael Osterholm and colleagues. A national expert on infectious diseases, Osterholm reviewed existing studies and concluded that the standard flu vaccine was only 59 percent effective in healthy adults younger than 65. That is lower than the 70 to 90 percent estimates offered in the past by public health officials.

There is little reliable data on the effectiveness of traditional flu vaccine in seniors, and nothing on Fluzone High-Dose. Osterholm still recommends it to seniors.

"Would I take it? Yes," he said. "At the same time, we have to be honest with the public about what we know and don't know."

Sanofi Pasteur has produced more of the vaccine this year than last and expects more interest. Whether individual clinics have the high-dose version depends on whether their distributors order vaccine from Sanofi Pasteur or other makers.

Hendrickson admitted some responsibility for taking the high-dose vaccine. She received paperwork at her Fairview clinic in New Brighton about Fluzone, but didn't read it before receiving the shot. She believes a discussion should have taken place.

"They ought to give patients the opportunity to say whether or not they want the high dose," she said.

Allyson Schlichte of Fairview Pharmacy Services said Fairview "generally recommends" that seniors get the high-dose vaccine and that they discuss the option with their providers.

Jeremy Olson • 612-673-7744