Monday, November 30, 2009

No Flu For You!?

Novel influenza A H1N1 “Swine Flu” vaccine in those over 65 years of age - not recommended.

Why Not?

One of the most frequently asked questions that I have gotten from my adult patients has been why, after decades of indoctrination from public health officials, the news and their own doctors, that the new H1N1 influenza A vaccine is not being suggested for those over 65.

This same age group commonly has at least one if not several underlying chronic medical conditions which in the past would put them into high risk for hospitalization or even dying from complications of influenza infection. It seems intuitive that they too should get this vaccine in addition to the usual seasonal flu shot.

The epidemic has however shown an unusual pattern in those at high risk. Since this new virus appeared in Mexico in early 2009, as well as throughout it’s spread across the world, including becoming the predominant seasonal winter flu in the southern hemisphere, it seems to hit the very young, pregnant women, and people under 65 who have chronic medical problems much harder than those over 65. The number of people 65 and up who have been hospitalized or worse has been unusually low for this flu pandemic. This is not to say that some older adults do get a classic influenza infection and get quite ill from time to time.

Some have conjectured that this unusual distribution of illness severity may be due to the robust immune response that younger patients mount in response to this influenza virus. Perhaps their immune systems overreact, which leads to damage of sensitive lung tissue and respiratory damage with fluid leakage and inflammation into the lungs. Older adults might have a somewhat less robust immune and inflammatory response and therefore not get into trouble from over responding to this virus.

It has also been observed that 25-30% of those over 50 years of age have antibodies that seem to match the H1N1 virus antigen similar to what one would get following a dose of the new H1N1 vaccine. Perhaps, through previous flu shots and/or exposure to old infections, this population already developed at least partial immunity. This age group might have even more immunity that is imprinted in the immune system and not readily evident on specific antibody testing. Additionally, those who got the swine flu vaccine in 1976 seem to have a very high level of matching antibodies to the current vaccine.

Due to manufacturing difficulties in the making of the novel H1N1 vaccine, there are not enough doses for those deemed at high risk, let alone extra doses for those over 65, regardless of any underlying condition. Some good news however,  suggests that this year’s seasonal flu vaccine might also give some partial protection from more severe H1N1 infections. Now that the manufacturers have finished making new doses of H1N1 vaccine this year, at least one company has restarted the manufacture of seasonal flu vaccine without the H1N1 antigens and this hopefully will be available by the end of 2009. This is especially timely as the vaccine manufacturers had to stop production of seasonal vaccine early to make the H1N1 vaccine and were unable to fill many orders fully for the seasonal flu vaccine this year when demand has been unusually high.