The H1N1 swine flu vaccines approved this week by the US Food and Drug Administration can be safely used by people with compromised immune systems, according to new recommendations from the American Academy of Allergy, Asthma & Immunology.
These would include people whose immune responses are weakened by medical treatments (such as for cancer or organ transplant) and those infected with HIV, the experts said.
Influenza vaccines can be made from live - but modified and weakened - virus, or they can be made from the harmless byproducts of the virus (so-called "killed" virus vaccines). According to the experts at the American Academy of Allergy, Asthma & Immunology (AAAAI), all of the injected H1N1 vaccines so far approved by the FDA are of the "killed" variety.
"There's never any harm with giving killed influenza vaccine" to immuno-compromised individuals, said Dr Kenneth Bromberg, director of the Vaccine Research Centre at The Brooklyn Hospital Centre in New York City.
There is one vaccine out there that those with weakened immune systems should avoid: the nasal spray form of the flu vaccine, FluMist. FluMist is already available in the US as a seasonal flu vaccine, and 3.4 million doses of an H1N1 version of FluMist are expected to be distributed nationally the first week of October, CDC officials announced Friday.
FluMist is derived from live (but very weakened) virus, so it could pose a problem for people with poor immune systems. The recommendation to avoid FluMist extends to people living in close proximity to an immune-compromised person, such as family members, because they could pass on the live virus to that individual, the AAAAI said.
No such threat exists for average people with robust immune responses, the experts said.
Primary immune deficiency
One question for some people with compromised immune systems is whether the flu shot will actually help them, given their poor immune defences.
People with so-called "primary" immune deficiency - rare immune deficiencies inherited at birth - can take the H1N1 vaccine, the academy said. "Although the antibody response may be poor or low [in these individuals], the cell-mediated response may be a helpful immune response to [fight] the virus," AAAAI President-elect Dr Mark Ballow said in a news release.
But, depending on their level of immune cell function, certain HIV-infected individuals may not be able to mount enough of an immune response to make flu vaccination worthwhile, the experts said.
"The issue is whether the compromised immune response might result in insufficient protection, not whether the inactivated H1N1 or seasonal influenza vaccine is excessively harmful," said Dr Paul Greenberger, president of AAAAI.
Safe in most HIV+ patients
"The CDC (US Centers for Disease Control and Prevention) notes that most HIV patients can receive the immunisation, and from earlier studies with seasonal flu shots, [it appears] there may be a reduced response if the number of CD4+ lymphocytes is less than 100/mm3," Greenberger said. "Better responses occurred if patients had CD4+ lymphocyte counts of at least 400."
He added that "studies haven't been published yet of H1N1 vaccination in HIV patients."
Routes of transmission
In other swine flu news, a study published in the September issue of the journal Risk Analysis seeks to quantify the risk from various routes of transmission of the swine flu virus. Researchers from the University of California, Berkeley, and the University of Illinois used sophisticated modelling and pored over the available data on four key means of person-to-person H1N1 transmission.
They speculate that hand contact with a contaminated surface brings a 31% risk of actual infection; inhaling tiny particles laden with virus in a room brings a 17 percent likelihood of infection; close contact where coughs spray viral-laden droplets onto the eyes, nostrils or lips brings a 52% chance of infection. Inhaling relatively large particles carrying virus when three feet or nearer to an infected person carries only a 0.52% risk for infection, the research team said.
According to the researchers, the study strengthens current recommendations to cover the mouth when coughing and to disinfect commonly touched surfaces. – (E.J. Mundell/HealthDay News, September 2009)