Posted by If you have or have had small children you may be all too familiar with earaches. When our kids were small we felt as if we were single-handedly supporting the amoxicillin makers. A major cause of middle ear infection is the organism Streptococcus pneumoniae (S. pneumoniae), which sometimes it invades other tissues and causes bacterial meningitis (not the kind that you read about killing healthy teenagers, but bad enough) and sometimes other body sites. It is also a cause of pneumonia in adults and was a common cause of secondary bacterial pneumonia in the 1918 flu. That was then. Now there is a vaccine for seven of the most common strains of this bug and it has made a dramatic difference in the rates of S. pneumoniae infections in children. In Massachusetts there has been a 75% reduction in severe invasive pneumococcal infections in children since 2001. So that’s the good news.
The news that isn’t so good, although it’s not terrible, is that the existing pneumococcal infections are increasingly being seen in strain 19A (actually a serotype), which is not included in the 7 strain pneumococcal vaccine. In 2000 only about 10% of the cases were 19A. Now they are over 40% 19A in the under 18 age group. The 19A strains are also more drug resistant, although even for the drug resistant variety there are alternative drugs that will work.
So are the 19A infections worse? The CDC report states there was no “significant” difference in outcome for 19A drug-resistant, drug sensitive and non-19A cases:
In addition, no significant differences among the three groups were detected in the proportion of patients with meningitis, pneumonia, or bacteremia without focus, case-fatality ratios, rates of hospitalization (79% versus 68% and 59%, respectively), or longer hospital stay (64% with >4 days versus 40% and 51%, respectively). (CDC, MMWR)
Here I would take issue. The pesky word “significant” is ambiguous in this connection and can mean “clinically or epidemiologically” significant or “statistically” significant in medical parlance. Since the difference between 79% and 59% or 64% and 40% is clearly clinically significant, this can only mean the fairly large differences weren’t statistically significant, which here is a function of sample size. The proper way to say this would be to note that the data didn’t allow a judgment as to whether the differences seen were from sample error, a real difference or some hidden bias (unmeasured differences in risk factors in the compared groups).
The incidence rate for serious pneumococcal disease in the under 5 age in Massachusetts in 1990 was about 56 per 100,000 children. By 2000, when the 7 strain vaccine became widely available, it was down to 18/100,000 or less and has remained there since. Thus 19A seems to be taking the place of other strains, not adding to them. Data from 2005 indicate 95% coverage in the 1-1/2 to 3 year old target population for the three dose schedule.
The vaccine is still doing its job. Prevalent serotypes of various bugs change over time and this change might either be “natural” or one encouraged or revealed by vaccine use. I wouldn’t hesitate to have my children vaccinated today if they were babies and their children — my grandchildren — have or will receive this vaccine. But this is a developing situation we need to keep our eyes on.
The recent reluctance to make public the problem with polio vaccine in Nigeria traces to a fear the news would be grist for a developing and dangerous anti-vaccine movement. Understandable. but very risky. We need to be as clear-eyed as possible about vaccines, their value and the trade-offs they present. Along with the tragic loss of public confidence this strategy invites, comes another casualty of deviating from the truth: we begin to believe our own prevarication.
October 23, 2007
October 23, 2007
October 24, 2007
October 24, 2007