Flu vaccine’s ineffectiveness has doctors using new weapon

A sign informs patients about the spread of germs at the San Francisco Public Health Department offices in San Francisco, CA, on Friday, January 16, 2015. A sign informs patients about the spread of germs at the San Francisco Public Health Department offices in San Francisco, CA, on Friday, January 16, 2015. Photo: Michael Short / Special To The Chronicle Photo: Michael Short / Special To The Chronicle Image 1 of / 10 Caption Close Flu vaccine’s ineffectiveness has doctors using new weapon 1 / 10 Back to Gallery

This year’s flu vaccine is a remarkably poor match for the virus that’s infecting most people this season, so doctors and public health experts are urging aggressive use of antiviral drugs to treat influenza, especially for the sickest and most vulnerable patients.

This year, the vaccine cuts a person’s risk of getting the flu by about 25 percent — a sharp drop in effectiveness from the 50 to 60 percent that occurs when the flu shot is well matched to the influenza strains in circulation, according to the U.S. Centers for Disease Control and Prevention.

Less effectiveness means more people may be getting sick this year, and those who do get sick may have more serious symptoms. So the CDC has issued several advisories recommending that doctors and other health care providers give antivirals to all patients who are hospitalized with the flu, and anyone else who could benefit from the drugs.

In a hospital or urgent care center, it’s not always easy to tell who has the flu or who doesn’t without a lab test, which can take a day to get done.

“But the person who all of a sudden got severe aches and high fever and some respiratory complaints all at once — everything sounds like the flu? That’s the person we encourage to treat right away,” said Dr. David Busch, chief of the infectious diseases division in the Department of Medicine at California Pacific Medical Center.

Still on the rise

The flu has peaked in most parts of the country but is on an upswing in the Bay Area, local public health experts said. Four deaths from the flu have been reported in the Bay Area so far this year.

“It’s still on a very steep rise right now,” said Dr. Roger Baxter, co-director of the Kaiser Permanente Vaccine Study Center.

The predominant flu strain is a variation of Type A, subtype H3N2, that has drifted, or mutated, far enough from the strain for which public health experts had planned that the vaccine, which was manufactured more than six months ago, doesn’t have much effect on it.

Typically, drugmakers design the seasonal flu vaccine based on what’s circulated in the opposite hemisphere before the Northern Hemisphere flu season starts around October. That plan works about 80 to 90 percent of the time. This year, though, the Southern Hemisphere strain mutated between seasons.

In a well-matched year, the vaccine can prevent or greatly lessen symptoms in up to 90 percent of healthy young adults who receive it. For older people, the vaccine is weaker — often providing only about 60 percent protection, even in a well-matched year — but still highly recommended by doctors.

And doctors continue to recommend it this year, despite the poor match. Even a 25 percent reduction in risk is better than no protection at all, they say.

Meanwhile, without the safety net of a good vaccine, antiviral drugs to treat the flu are an important weapon, public health experts say. But they often are underused.

The CDC reports that only about 1 in 6 people seriously ill with the flu — in other words, hospitalized, often in the intensive care unit — is ever treated with antivirals. The reason they’re not popular may be that they’re not remarkably effective.

Studies have shown that in otherwise healthy adults, antivirals, when given in the first 48 hours after a person becomes symptomatic, can shave a day off the usually five- to six-day course of illness. Their effectiveness fades after that 48-hour window, because after two days a person’s immune system has kicked in and started to get rid of the virus on its own.

No sure cure

“It’s not a bad thing to save somebody a day when they can work or not have their head in a poultice or something. But these are not miracle drugs,” said Busch at California Pacific Medical Center.

Antivirals may be more effective in severely ill patients, who haven’t been well studied in clinical trials of the drugs, said Dr. Henry Chambers, chief of the Division of Infectious Diseases at San Francisco General Hospital. And even if the antivirals aren’t more effective, those people are sick enough that doctors should be using any tool that might shorten or lessen their symptoms.

“Certainly if someone is hospitalized and they have influenza, you give them antivirals,” Chambers said. “Efficacy is going to be better if someone comes in early. But for a critically ill patient, you wouldn’t withhold therapy if it’s 49 hours instead of 48.”

He also recommends antivirals for non-hospitalized people, including otherwise healthy adults who get the flu. People with other health conditions — such as heart disease or diabetes — should be especially proactive in asking their doctors about antivirals.

“I would educate myself to know about antivirals if I was in that population,” Chambers said. “You want to do everything possible to improve your outcome.”

Erin Allday is a San Francisco Chronicle staff writer. E-mail: eallday@sfchronicle.com

Stay healthy

The flu season is picking up in the Bay Area and it’s not too late to get a flu shot. To find a location, check out this vaccine finder at http://flushot.healthmap.org/.