Browse any news publication and you will surely come across a catchy health-themed headline that s meant to grab your attention, for example: Living at High Altitudes is Linked to Higher SIDS risk. If you re a parent living in mile-high Denver, this headline will stop you in your tracks. How can you not read that? The article does even more harm as it makes no mention of the actual data which show a merely-marginal increase in SIDS risk. And furthermore regardless of altitude, the incidence is still less than 1 per thousand births. With these facts left out, the reader is left with a sense of fear that the study s data aren t strong enough to elicit. In reality, sensationalizing epidemiological studies does a lot for the publication s bottom line but does little for public health.
We point this out frequently, but it bears repeating: epidemiological studies are weaker than other types of studies because they can fall into the famous causation vs. correlation pit. However, this doesn t mean they are all bad as they can lead researchers down an important path towards finding a biological mechanism. This now appears to be the case with the Haemophilus influenzae Type B (HiB) vaccine and a child s risk for developing acute lymphoblastic leukemia (ALL).
Let s take a trip down memory lane. In early 2011, an epidemiological study (and other studies would find similar results) found that children who received the HiB vaccine had a robust 40% reduced incidence of ALL. At the time the study was met with some skepticism as scientists wondered how a vaccine against bacterial meningitis could also protect children against ALL, one of the most common childhood cancers. ACSH s Dr. Gilbert Ross cautioned that: We tend to take the view that drawing any conclusions from studies like this, which purport to correlate county-wide interventions with possibly unrelated outcomes, should be regarded with suspicion.
Flash forward to present day, and a study released in Nature Immunology can now backup that epidemiological study with a biological mechanism. A multi-center group of researchers, American and European, led by Dr. Markus Müschen of the Department of Laboratory Medicine at the UCSF, came up with an elegant explanation. The authors proposed mechanism proceeds as such: usually infection with HiB elicits a well controlled and regulated immune reaction; however, in a fraction of cases there is an overreaction to the bacterium which is characterized by 2 enzyme classes being turned on in some white blood cells. These enzymes can disrupt the cell s chromosomal integrity and can lead the cell down the road to becoming cancerous. However, if a child receives the HiB vaccine the immune response does not involve these enzymes.
ACSH s Nicholas Staropoli says: We weren t wrong to caution people 4 years ago about the initial reported link, but now we are really excited about it. First of all we have yet another reason to love and recommend vaccines, but we also have the seemingly rare opportunity to see an epidemiological finding be validated with a plausible biological mechanism.