Why we vaccinate–mandatory flu vaccines reduce risk of hospitalization

flu-shot-smiley-face

Updated 28 November 2014.

According to the unsurprising results reported in a new study, published in the Morbidity and Mortality Weekly Report, in areas where laws mandate that children receive a seasonal flu vaccination, before entering preschool or day care, the rate of flu-related hospitalizations drops significantly. In this study, after Connecticut enacted a law that mandated the vaccine, the rate of children requiring hospitalization because of the flu declined by 12%.

Connecticut’s regulation for flu vaccination (pdf), which took effect in 2010, increased the uptake of childhood flu vaccinations from 67.8% to 84.1%. According to Dr. James Hadler, the lead researcher for the study, “That difference, we feel, has resulted in children attending daycare being better protected against influenza and its severe complications.”

Even though Connecticut’s regulations for flu vaccination allows for some exemptions (the child has a scheduled appoint for the shot soon after the start of school, medical contraindication, or religious belief), it’s obvious that the effort was highly successful in driving up the level of uptake of the flu vaccination, a vaccine that is often ignored by parents for occasionally odd reasons. Continue reading “Why we vaccinate–mandatory flu vaccines reduce risk of hospitalization”

Potential apocalyptic influenza pandemics-H2N2

Posting at the Brooklyn Navy Yard during the 1918 Spanish Flu pandemic.
Posting at the Brooklyn Navy Yard during the 1918 Spanish Flu pandemic.

From January 1918 through December 1920, humanity suffered through the one of the worst pandemics of infectious disease for the last 100 years or so. The world was hit by what was called the Spanish Flu (not because it started there, but because news of the flu was censored in most countries involved in World War I, but Spanish news wasn’t censored, so it appeared that Spain was being devastated by the disease). According to conservative estimatesdespite how antivaccination cultists portray flu pandemic estimates, nearly 500 million people worldwide were hit with this flu, and somewhere between 50 and 100 million people died, nearly 5% of the world population at the time. Moreover, the majority of deaths were amongst healthy young males, not, as antivaccination tropes often claim, just to those who are sick and weak already.

A recent article called the 1918 flu pandemic the “mother of all pandemics,” and not just for some rhetorical, literary effect. In fact, the 1918 flu, an H1N1 subtype, is the mother of nearly all subsequent influenza A (for avian) pandemics since 1918–in other words, the original H1N1 subtype has mutated into nearly all of the other subtypes of avian flu.

For example, H2N2 influenza A viruses, which derived from a mutation in the H1N1 subtype while it circulated in birds, were the cause of the 1957-1958 pandemic, which killed nearly 1.5 million people worldwide. Currently, the H2N2 subtype has disappeared from humans, but it persists in wild and domestic birds. Claims that the subtype is extinct are premature.

Unfortunately, a potentially dangerous reemergence of the H2N2 subtype in humans continues to be a significant threat due to the absence of immune system memory of the H2N2 within the adaptive immune system of individuals under the age of 50. In other words, those individuals who were born after 1963, have no immunity to H2N2, and may be susceptible to it.

Researchers examined the presence and potential risk of over 22 strains of avian H2N2 viruses isolated from domestic and wild birds over the past 60 years. Most of the strains replicated in mammalian cell culture, and three transmitted to ferrets, usually used a model for human infection from new flu viruses. The H2N2 virus remains highly pathogenic for mammals, including humans, and there continues to be a major risk for quickly moving from the avian reservoir to humans

The point of this story is not to say that a global apocalyptic event is just around the corner, but it could be. It’s just that if you speak with any infectious disease specialist, their greatest fears are HIV/AIDS and influenza, not some obscure novel pathogen arising quickly then dying out of existence. The influenza A virus mutates quickly, allowing it to avoid human humoral immune responses, it transmits from other species to humans easily, it spreads quickly, and it can be deadly. As recently as 2009, the H1N1 pandemic killed approximately 150,000-500,000 people worldwide.

Of course, the CDC constantly monitors when the virus jumps from the bird reservoir to humans, and if given enough time, can prepare a vaccine to help prevent it. Let’s hope people are smart enough to get it.

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Key citations:

BBC News – La Nina ‘linked’ to flu pandemics

BBC News – La Nina ‘linked’ to flu pandemics.

An interesting article published in the Proceedings of the National Academy of Sciences correlates the La Niña conditions in the equatorial area of the Pacific with flu pandemics.  The authors propose that the La Niña conditions (which upwell colder water to the surface, changes migration patterns of migratory birds.  Since birds are one host for the influenza virus, these changed migration patterns may change how the birds interact with other species moving new influenza subtypes into different parts of the world.

We are, however, a long way from predicting a pandemic based upon a La Niña event.  Right now, the authors can only correlate pandemics and the Pacific circulation patterns in just four cases:  the Spanish Flu of 1918, the Asian Flu of 1957, The Hong Kong Flu of 1958, and the Swine Flu of 2009.  It’s hard to make a case for causality based on these four data points, but the authors do lay out a compelling argument.

Whenever I critique a correlation vs. causation argument, I first determine if the causality is even possible.   I often make the argument that MMR vaccinations cause broken arms in 12-16 year old girls, because a small, but significant proportion of kids being vaccinated get broken arms (or car wrecks, gastroenteritis, an itchy nose, and angry comments to their parents).  However, there is no physiological, biological, or scientific reason why a broken arm might result from a vaccination.

In this article, the authors do make a scientifically plausible case that avian migration patterns do change in La Niña events, so they are on the path to providing outstanding evidence to support this hypothesis.