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Posted on 01/30/2009 1:04:48 AM PST by neverdem
By Victoria Stagg Elliott, AMNews staff. Posted Jan. 19, 2009.
How much difference does the flu shot really make?
Various studies offer wide-ranging conclusions. One, for instance, found that seasonal influenza vaccine halves elderly deaths from any cause in the winter months. But another found it has no impact at all on this age group's health. These and other conflicting findings are pushing public health officials and scientists to look for better ways to quantify the preventive's impact.
"Flu vaccine works in elderly people, but what we don't have is a complete picture of what the true effect might be and how it might vary from season to season," said David Shay, MD, MPH, a medical officer in the Centers for Disease Control and Prevention's influenza division.
Consider the following results.
A meta-analysis in the March 15, 2002, Vaccine reported that inactivated influenza vaccine in those older than 65 who did not live in institutions cut influenza-like illness by 35% and all-cause mortality by 50%. Another paper, in the Oct. 4, 2007, New England Journal of Medicine, pooled data on 18 cohorts of 713,872 elderly people and found that vaccination was linked to a 27% cut in hospitalization from pneumonia or flu and a 48% reduction in the risk of death.
Other research offers an alternate perspective.
A study in the Feb. 14, 2005, Archives of Internal Medicine suggested that the decline in influenza-related mortality in the 1970s among those ages 65-74 came from immunity acquired during the 1968 pandemic. Also, vaccine coverage increased from between 15% to 20% in 1980 to 65% in 2001, but this increase could not be connected to declines in mortality. Another study in the Aug. 2, 2008, Lancet examined 1,173 elderly people with community-acquired pneumonia and 2,346 controls. The study found no link between flu vaccination and a reduced risk of this illness.
The authors of studies questioning the effectiveness of the flu vaccine say, however, that the take-home message from their work is not that this immunization doesn't work. Rather, the data saying it does are not as strong as they would like.
"The true benefit is somewhat unknown," said Lisa Jackson, MD, MPH, one of the authors of the Lancet paper and a senior researcher at Group Health Center for Health Studies in Seattle. "For the individual, it's reasonable to continue getting influenza vaccine, but we need a more realistic message about the benefits they might expect. [A] 50% reduction in all-cause mortality is just not plausible in any sense. Influenza only causes 5% of winter deaths at most."
But the kind of placebo-controlled randomized trials that might quantify the benefit once and for all are unlikely. Numerous such investigations already have been conducted, but they were carried out in young and middle-aged adults rather than those older than 65 -- the demographic that makes up the biggest target of vaccination efforts and suffers the greatest ill effects from this respiratory infection. A trial focused on this age group would be considered unethical. And the observational studies researchers have used to help answer the question may be confounded by other factors. For instance, according to those who question the more positive papers, results may be inflated by the possibility that the elderly who get the vaccine may be fitter than those who do not.
"The seniors who are healthy and are able to go get a flu shot are less likely to get pneumonia or die. The benefits [of the influenza vaccine] are probably real but rather small," said Michael L. Jackson, MPH, PhD, lead author of the Lancet paper. He wrote it as a postdoctoral fellow at Group Health.
In addition, the impact may not be big enough to detect in smaller studies. And because the evaluated endpoints vary widely, it can be tough to compare one to another.
"We have to be very careful about making sure that we understand what the study populations are and what the outcomes are," said Kristin Nichol, MD, MPH, the lead author of numerous papers finding benefits from influenza vaccine, including the 2007 NEJM article. She also is associate chief of staff for research at the Minneapolis Veterans Affairs Medical Center. "It's really important to look at the entire body of evidence."
But these investigations are complicated by the nature of influenza vaccine, which aims at a constantly moving target. The viral strains it includes change every year. Circulating viruses shift constantly. And every season is different in regard to severity and spread.
A study in the Jan. 15 Journal of Infectious Diseases found the vaccine's effect in preventing an infection that requires medical attention ranged from 5% during the 2004-05 season to 37% in 2006-07. These rates stemmed from the differences between what was in the vaccine and what was moving around in the community.
Public health officials are trying to get a better handle on the vaccine's actual impact, and advocates say the effort is still a good idea. The CDC is running several projects seeking an answer. And according to the CDC Web site, when the vaccine is well-matched to circulating strains, immunization reduces the risk of getting influenza by 70% to 90% among healthy adults. It may be less effective in elderly people and very young children, although it still provides protection against severe complications.
"Influenza is a pretty good vaccine. It's far from perfect, but there is not any doubt that there's some benefit," said William Schaffner, MD, president-elect of the National Foundation for Infectious Diseases and chair of the Dept. of Preventive Medicine at Vanderbilt University School of Medicine in Nashville, Tenn.
More than 143 million doses were delivered this season. The National Influenza Vaccine Summit, which is sponsored by the American Medical Association and the CDC, will meet in Dallas May 19-20 to discuss this season and lay plans for the next.
The print version of this content appeared in the Jan. 26, 2009 issue of American Medical News.
Interesting, a pandemic in 1968. I have never had the flu shot, I have never had the flu. I was born in 1968, July so at six months or older, I would have been capable of producing antibodies. Of course, I am still young. I will wait for the vaccine when I am older.
My hubby has had the flu once, never had a vaccine. Born after 1968.
flu shot efficacy study review ping
No correlation, I was born in 57, never had a shot, never had the flu. Staying away from children helps, they are germ farms if they go to public school.
Most flu vaccines are preserved with mercury. No thanks! And besides, vitamin D from sun exposure or supplementation with D3 is much safer and effective, IMH, but informed, O.
You would have been able to produce antibodies at 11 years of age to the 68 flu. That adds evidence. My kids are in public school, they have gotten a mild flu from the vaccine. I stayed cooped up with them for a week two years ago. I did not get the flu. So, anyway, I am interested in this 68 flu.
They claim the shots will not give you the flu.
I got the flu shots three years in a row, One year I got Pneumonia and bronchitis, the next two years the bronchitis damned near killed me. On the fourth yar i refused the shot had a great winter, no colds, this year I refusd it again, so far had a cold,but not too bad. I dont want the flu shot again.
Now this could just be coincidence, but I am avoiding the flu shot.
The only time I got the flu was when the Navy forced shots on everyone.
Since then, 28 years, I have had one mild case of flu.
I would not be at all surprised to find that people that are concerned enough about their health to have a flu shot have a lower death rate than those who don't. This doesn't mean, though, that there is a cause and effect relationship between flu shots and general mortality rates. This is a typical naive' statistical error: confusing correlation and causation.
The Hong Kong flu in 1968 was a nasty. I knew adults who were laid out for weeks, unable to eat more than one or two crackers with peanut butter on them made by their kids. One later said that fully recovery from its debilitating effects took months.
“The Hong Kong Flu was a category 2 flu pandemic caused by a strain of H3N2 descended from H2N2 by antigenic shift, in which genes from multiple subtypes reassorted to form a new virus. The Hong Kong Flu pandemic of 1968 and 1969 infected an estimated 500,000,000 people with a low death rate. Fifty million people were infected in the United States, resulting in an estimated 34,000 deaths.”
It is interesting that it would lay you out, but had just normal mortality rates. Adults tended to suffer more from the disease than children, and I noted that none of my peers was out of school for any length of time.
Todays vaccine will not give you the flu because it contains only dead flu virus. That was not true of the old live virus vaccine.
We caught the flu every winter until we began taking the killed flu vaccine, we have not had the flu since. We would never fail to be vaccinated.
There are viruses out there not covered by the vaccine so it is possible to take the vaccine and still catch one of those other viruses that are not in the current vaccine.
Also if you have already been exposed to the flu before you take the shot you could still have a light case of the flu. All of this info came from several doctors that I trust.
Don’t be too quick to jump to conclusions. There is a good possibility that when you were vaccinated, your immune system was already in a weakened state—conversely, it might have been slightly hyperactive, common among young adults.
In a weakened state, being vaccinated might have stressed it further, making you susceptible to acute viral nasopharyngitis, aka “colds”, and other URTIs, which may have been dormant in your sinuses, then activated. People are loaded with such pathogens (even MRSA and NF, the “flesh eating bacteria”) are commonly there, as idle, opportunistic threats.
Conversely, if your immune system was a little too active, it would easily overreact to the introduction of the antigens in the vaccine, treating it as if it was a new and deadly flu, which it isn’t.
Flu vaccines are usually created like this. In the name of a particular flu, say “H1N1”, the “H” factor is how the viruses enter human cells, and the “N” factor is how they get out again. Each of these factors has 8 gene segments. Scientists slice off two of the H, and two of the N gene segments, and splice them onto a different kind of virus genes that affects chicken, but not people.
When this is injected, your immune system spots those 2 out of 8 H gene segments, and 2 out of 8 N gene segments, and creates antibodies to fight any virus that has those 4 segments. Otherwise, the chicken virus just sits there and doesn’t infect you.
However, a hyperactive immune system might misinterpret the harmless chicken virus as a new and lethal threat, so the immune cells and the chicken viruses duke it out in your lung tissues. Hence the severe bronchitis.
Immune systems tend to settle down after the age of 40, so are much less likely to get such “false positives”. So if you got such a reaction to a flu shot when younger, it may no longer be a problem if you are over that age.
Cheers!
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