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Updated 22 minutes ago

Each year during the flu season, I am bombarded by patients and friends telling me that despite receiving the flu shot, they end up catching the flu.

While many of those individuals may have actually had an infection with another respiratory virus that mimics some of the symptoms of influenza or contracted influenza before the vaccine had enough time — about two weeks is needed — to provoke immunity, some people truly have vaccine failure.

Trying to convince them that the flawed vaccine nonetheless possibly prevented them from being hospitalized (or worse) or spreading the virus is usually no consolation to those who feel like the vaccine did not deliver on its promise.

This phenomenon makes it much more challenging to convince someone to get a flu shot.

Unfortunately, it also boosts the efforts of those who, inexplicably, oppose mandatory health care worker vaccination policies.

Why does this occur?

Influenza vaccination campaigns are a staple of public health programs. Flu vaccine campaigns have been in place since the flu vaccine was developed for the military in the 1940s by a young pre-polio Jonas Salk and others. This decades-old vaccine and the technology used to manufacture it are essentially what humanity has used to guard against flu since that time.

However, this vaccine is not a panacea in the way the smallpox vaccine was for smallpox. The influenza virus itself poses special problems for vaccines. First, there are several strains of the virus that, in any given season, may dominate or co-dominate requiring a robust vaccine to include multiple strains of the virus. Second, the various strains of the influenza virus are not static and they change or drift, to some degree every year, sometimes requiring the vaccine to be reformulated on a yearly basis. The process of vaccine strain selection occurs months before the flu season, giving manufacturers ample time to produce the product in sufficient quantities before the onset of the flu season. However, with such a long lead time and such a tricky virus, surprises are bound to occur. For instance, public health authorities may be off in their predictions resulting in vaccine strains that are mismatched to the circulating strain. A mismatched vaccine will cause vaccine effectiveness rates to plummet. This is exactly what happened in 2014-2015 when a drifted variant of the virus rendered the vaccine largely ineffective. Indeed, the Holy Grail of influenza vaccination is an almost mythical universal vaccine. This type of vaccine would be more like vaccines such as those against tetanus, polio, and measles, and do not require updating.

Another aspect of what ails the influenza vaccine field is the fact that almost all are grown in chicken eggs, just as they were when the vaccine was first invented. Using chicken eggs in the vaccine process poses a few important problems. The most relevant of these issues to vaccine effectiveness is that when a vaccine strain is put in a chicken egg, evolutionary forces take hold and the virus adapts to life in the egg and that adaptation can change the vaccine strain in such a way that, though more adapted to a chicken egg, it no longer fully resembles the viral strain it is intended to protect against. Consequently, vaccine effectiveness is compromised. Chicken egg vaccine technology also poses significant problems when it comes to pandemic influenza preparedness as the speed and versatility of this technology are limited.

What are the solutions?

While development of a universal flu vaccine remains a goal for several researchers and vaccine companies, it is — even in the most optimistic estimates — still years away. While this important work continues, there have been some significant attempts to improve vaccination effectiveness rates. Thus far, these modest improvements have been targeted to those above the age of 65 who are higher risk for severe influenza and whose immune response to the ordinary vaccine has blunted with age. There are two alternative vaccines that can be used in this population: a higher dose vaccine in which four more times the amount of viral material is included and an adjuvanted vaccine in which aluminum is used to heighten the stimulation the immune system the vaccine induces. Additionally, an innovative vaccine grown in cells using recombinant technology, with zero dependence on chicken eggs, is also available. There is some suggestion that avoiding chicken eggs altogether may improve the vaccine's effectiveness as no evolutionary chicken egg adaptations occur during production, preserving the integrity of the vaccine strain.

Influenza is a prolific infectious disease killer. Each year thousands of Americans die from this virus. Pandemic influenza strains, like the one that circulated in 1918, can kill at an amazing rate and have the capacity to change the entire structure of the world. Standard vaccination, despite its many limitations, is the chief and only means of mitigating the effects of this virus and is something I unequivocally recommend to everyone. The perennial threat of seasonal influenza and the looming threat of pandemic influenza underscores the desperate need to develop what have been called “game changing vaccines” that are highly effective, able to be rapidly produced in a manner not dependent on chicken eggs, and are devoid of the need for annual updating.

When it comes to the flu vaccine, it can be hard to love the one we're with, but important improvements — including the recombinant egg free vaccine — have much promise and will hopefully lead to the game changing vaccine that will finally be a match for the wily influenza virus.

Dr. Adalja is a Pittsburgh-based infectious disease physician who blogs at www.trackingzebra.com. Follow him on Twitter: @AmeshAA.

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