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11/5/2003

Pharmacists Mull Transmission Risks of FluMist

Kate Traynor

As FluMist, MedImmune Inc.'s live attenuated intranasal influenza vaccine, makes its debut for the 2003–2004 flu season, health care providers consider the possibility that the product could cause illness in patients with a weakened immune system who come into contact with recent vaccinees.

"It's something to think about," said Mary S. Hayney, an associate professor of pharmacy at the University of Wisconsin (UW) School of Pharmacy in Madison whose clinical practice involves lung transplant patients at the UW Hospital and Clinics.

FluMist is indicated for the prevention of influenza in healthy people ages 5–49. The vaccine should not be administered to children under age 5 or adults 50 years or older. Other populations that should not receive the vaccine include people with diabetes mellitus, heart or lung disease, or asthma. People with a weakened immune system should not receive FluMist.

According to the Centers for Disease Control and Prevention (CDC), studies have shown that recent vaccinees can shed FluMist's attenuated influenza virus. It is unclear whether the virus can cause illness in those exposed to it, including people with an immune deficiency.

"The risk is largely theoretical," Hayney said. "There is no evidence of definitive harm among adults. To be honest, there's no evidence of definitive harm among anyone."

Still, her advice to health care providers about the inadvertent exposure of patients to the attenuated virus is to "be cautious until we do know more" about the safety of FluMist.

An element of caution is apparent in the product's labeling, which recommends that FluMist recipients avoid close contact with immunocompromised people for at least three weeks after receiving the vaccine.

CDC likewise recommends that health care workers and other people who come into contact with immunosuppresed patients receive the traditional inactivated influenza vaccine instead of FluMist. 

"We're telling [our] employees they should not be getting FluMist because of the concerns of them passing it on to immunocompromised patients," said Rita K. Jew, clinical coordinator at Children's Hospital of Philadelphia.

Jew added that the hospital is "waiting for infection control to come up with a policy on other people, like visitors and other children who might have received the vaccine, who might be coming into the hospital."

The cold-adapted virus in FluMist replicates well enough in the nasal passages to induce protective immunity but does not tolerate the warmer environment of the lungs. But it is, nonetheless, a live virus with the potential for disease transmission.

"We definitely know that you can easily pass it on to other people because it's replicating in the nasal mucosae," Jew said. "The question is whether it will pose a risk to immunocompromised patients—if, for whatever reason, it might replicate in the lungs. The vaccine is made in such a way that it's not supposed to replicate in the lungs. And theoretically it shouldn't cause a problem. But since there's no data, we need to be on the conservative side until we know exactly what's going on."

Jew added that Children's will be giving only the inactivated vaccine to patients.

"We don't carry FluMist in the hospital right now because of its indications for use," she said. "There's really no place for the vaccine in the hospital."

Carla Frye, director of ASHP's Section of Clinical Specialists and Scientists, pointed out that live vaccines that protect against several diseases—polio, varicella, measles, and mumps—are in common use and may pose a risk for immunocompromised patients who come into contact with recent vaccinees.

"It's not a new problem," Frye said in reference to FluMist. "It's just a new drug."

Christopher James, a clinical pharmacist at Christiana Care Health Services HIV Community Program in Wilmington, Delaware, expressed similar sentiments about inadvertently exposing immunocompromised patients to FluMist.

"I think that the same concerns need to be exercised as with any live vaccine," he said.

James noted that current clinical data on real influenza exposure risks for HIV-infected patients are not adequate. "It's hard to say from transmission studies whether you're putting somebody at risk" for disease, he explained.

James noted that influenza vaccination is a standard procedure at the clinic. "We do a lot of flu vaccination of our patients," he said. "It's just a sensible thing to do."

He added that assessing patients' exposure to live vaccines is part of the influenza vaccination workup.

"We take the opportunity, when vaccinating our patients with the regular flu vaccine, to ask whether other people near them are being vaccinated with a live virus," he noted.

James agreed that HIV-infected patients should avoid contact with recent FluMist vaccinees. "The safest thing is to be on the conservative side, because we don't know what risk that vaccine poses," he said.

But he did put the theoretical risks posed by the attenuated FluMist virus into perspective: "It's not like oral polio vaccine, where you put somebody at risk for contracting a really terrible, life-threatening illness," he said.

Judianne C. Slish, clinical assistant professor at the School of Pharmacy and Pharmaceutical Sciences at the State University of New York, University at Buffalo, said that the exposure of patients to live virus shed by vaccinees was a major topic of discussion about a year ago.

"I would say the biggest scare was when everybody was talking about smallpox vaccination," she said. Concerns about inadvertently spreading the product's vaccinia virus, Slish said, led the hospital to recommend that "anyone in any sort of immunocompromised state—transplant patients, HIV patients—[not] get anywhere near someone that was recently vaccinated, because they could shed the virus."

"I think that's the first time that there was a heightened awareness about this issue," she said.

Slish noted that she and her colleagues at the HIV clinic "are aware of the CDC recommendations" that health care workers who might come into contact with immunologically vulnerable patients receive the inactivated influenza vaccine.

"I would never get the live attenuated form, because I am around individuals that are immunocompromised," she added.