Flu 101: To Fight the Flu, Prepare for It

David L. Katz

This blog platform, Eat + Run, is inevitably about matters related to, well - eating and running - or more generically, diet and physical activity. Addressing influenza in this context is a bit of a stretch, although there is a case to be made that one of the best defenses against the flu, as against almost any acute illness, is robust good health at the outset - and eating and running figure prominently there. Mostly, though, the editors have indulged me in wandering a bit out of the customary bounds, and my thanks to them for it.

There's good reason to be talking now about influenza. The U.S. Centers for Disease Control and Prevention, which monitors global influenza activity with one of the most robust systems of surveillance in all of epidemiology, had indicated that flu is active in the U.S. in at least half of the states now and spreading briskly. Media outlets are spreading the word in tandem with the germ.

[See: Top Recommended Flu Products.]

The strain of flu circulating this year is, thus far at least, predominantly the same H1N1 strain that caused some degree of both panic and pandemic in 2009. The panic may have been excessive, but the virus did kill nearly 300,000 people that year, so it warranted respect, as it does now.

Let's start with a little "flu 101." The "flu" refers to influenza A, an upper respiratory infection caused by a virus. The virulence, or strength of the flu strain, varies every year. The illness caused by the virus is never pleasant, but when the strain is very virulent, the illness can be severe. Although the flu, per se, generally does not cause death in otherwise healthy people, more than 30,000 premature deaths each year in the U.S. alone are attributed to influenza, mostly in older adults, the very young or those prone to complications due to prior illness. Complications of the flu, including death, are more common in smokers than non-smokers.

When the flu strain is especially severe, being the right age or having generally good health make for less reliable defense. The single greatest infectious disease calamity in all of human history was not plague, or typhus or smallpox - it was the 1918 flu pandemic, which killed as many as 50 million. Those who don't respect the flu just aren't paying attention.

Of course, there was no vaccine in 1918 as there is now, and that may partly explain why we have seen no commensurate outbreak since. But vaccination is only protective when we roll up our sleeves, and too few of us do.

[Read: Why You Should Get the Flu Vaccine.]

Most vaccines provide protection over an extended period of time. The flu vaccine is unique because the influenza germ itself is unique and exceptionally wily. It undergoes a process known as "antigenic drift" that changes the germ's surface proteins every year so that this year's flu is unaffected by last year's vaccine. The CDC and the World Health Organization track the emergence of flu strains in Asia each year and develop a vaccine based on the particular surface proteins that predominate. The flu bug is also subject to more abrupt changes, known as "antigenic shift," which occur when flu strains mingle with one another. That is the process that produces pandemic strains of flu.

Immunization works by priming our immune system to attack the virus by stimulating it with those surface proteins, known as antigens because they "generate" the formation of "antibodies." The flu antigens in the vaccine look like the flu virus to our immune system. After the vaccine, if we are exposed to the flu, our immune system recognizes the germ as a foreign invader against which it has laid down preparations and launches a quick and effective attack. When all goes as hoped, the virus is eradicated before we get sick.

In general, it takes our immune system several weeks after exposure to antigens to develop a robust supply of antibodies. Consequently, the best time to have the flu vaccine is before the bug is established among us. But this can be a case of better late than never, and the CDC is advising that it's not too late.

Of course, you may be among the many who are dubious about flu vaccination specifically and immunization in general. I will address this bluntly: By and large, doubts and conspiracy theories about vaccines are the privilege of the very societies that are the greatest beneficiaries of them. Stated differently, populations succumbing to polio and smallpox don't tend to fret the theoretical harms of vaccination. We needn't go so far; high rates of measles, mumps and rubella tend to make vaccine enthusiasts of parents as well.

[See: Best Children's Hospitals 2013-2014.]

For starters, the flu vaccine does not cause the flu - ever. It can't because the vaccine does not contain a virus, just proteins. There is no infectious agent in the vaccine; viral proteins cannot replicate or cause disease. Everyone knows someone who swears he or she got the flu after the flu shot. The problem is, we often refer to any severe upper respiratory illness as "the flu" (while referring to less severe cases as "a cold"), and viral upper respiratory infections are common in the fall and winter when the flu shot is given.

If you get a viral infection shortly after getting the flu shot, you may assume it is due to the vaccine even though it is not. The immune system response to the vaccine can at times make people feel slightly ill for several days, but that's a far cry from a true bout of flu, which tends to last more than a week and cause, among other things, severe muscle pain and high fever.

[See: Top Recommended Health Products: Pain and Inflammation.]

There is also some doubt about the effectiveness of the flu vaccine. It is certainly far from perfect, and the elderly - who most need protection - may need two inoculations to get it. But leaving aside some of the subtleties that complicate measuring vaccine effectiveness in real-world settings, and applying even a low-level estimate of overall vaccine effectiveness, routine flu vaccination produces a decisive overall benefit compared to just taking our chances with the flu.

We should also recognize that when it comes to contagion, not one of us is an island. While true that the elderly most need protection and benefit least from vaccination, there is another way to protect our older loved ones: vaccinate ourselves and our children. People who can't get the flu can't transmit the flu to those most vulnerable to it and its complications.

Whatever your doubts about the influenza vaccine, it is an established fact that immunization is many times - many times - safer than the flu itself. That does not mean the flu is a plague, nor that the vaccine is perfectly safe. Nothing in medicine and little in life is perfectly safe. Harm from the flu vaccine is possible but a highly remote risk. For what it may be worth to make this personal, I readily accept that risk every year not only for myself, but for my beloved wife and children as well. I put the arms of the people I love most on the planet where my mouth is on this topic.

[Read: How to Keep Your Loved One Safe in the Hospital.]

There are several reasons why the potential harms of flu vaccination may loom much larger in the imagination than they actually are. First, any adverse event - an allergic reaction, the now exceedingly rare case of Guillain-Barré syndrome - is amplified many orders of magnitude by repetition in the blogosphere. One case, appearing on 50,000 websites, exerts the influence of 50,000 cases.

But at least as important, we are generally blasé about risks that lack the intrigue of conspiracy. So, for instance, consider if the flu infects 1 in 5, and kills 1 per 10,000 people infected. There is certainly a good chance you, if healthy, would not be among those who get the flu. There is a very good chance the majority of people you know would not get the flu either. And you are very unlikely to know anyone who is killed by the flu.

But 1 in 5 infections means 60 million or so infections nationally. One death per 10,000 of these infections might be invisible in your circle of friends and family, but it would mean 6,000 deaths nationwide. This is consistent with a quite mild flu season in the U.S.

In contrast, the most dangerous flu vaccine in history - the notorious swine flu debacle of 1976, when there were adulterated vaccines in the mix - was associated with 25 deaths. That's bad - but it is more than two orders of magnitude less bad than even the mildest of flu seasons.

Another argument I hear against vaccination is like that proverbial "Uncle Joe" everyone knows, who smoked three packs a day and lived to be 119. It could happen, but I wouldn't bet the farm on it. Uncle Joe is that rare character who somehow comes away from a train crash with a minor flesh wound. The rest of us are mortal.

[See: 6 Dangerous Games Your Kids Should Avoid.]

There is something more fundamentally wrong with the "I've-never-gotten-the-flu-and-therefore-don't-need-to-be-vaccinated" stance than the Uncle Joe fallacy. Let's face it - those who were ultimately beneficiaries of small pox or polio immunization never had small pox or polio either. If they ever had, it would have been too late for those vaccines to do them any good.

The trouble with serious illness is that one time can be one time too many.

Familiarity breeds contempt, or at least complacency, and perhaps the annual return of influenza has induced that response. Perhaps that's why we seem to be dismissive of this germ and overlook what a serious illness it can be. But that tendency can put us in peril.

Perhaps the strongest argument against immunization is that it represents science interfering with a natural, native balance. The notion is that our immune systems can handle the job without outside interference. The trouble with the "just-leave-it-to-nature" platform is that the nature in question, the nature to which our immune systems are adapted, is long, long gone. It does not exist today, and it has not existed for millennia. The biological norm for Homo sapiens is life in small, roving, isolated bands.

There are some very important biological implications of small, roving, isolated bands. Small roving bands do not propagate highly virulent pathogens because being highly virulent in a small population is the fast track to extinction. There is an advantage up to a point in genes that make germs good at getting from one person to the next, invading and infecting. Making someone sick is advantageous, too, because while the attendant misery is incidental, coughing and sneezing are great means of transmission. A germ that makes us cough and sneeze is actually enlisting our assistance in getting a fast pass to the person three feet away.

[Read: How Hospitals Can Better Prevent and Cope With Infections.]

But the genes that make bugs good at making us sick can, of course, go further - and make the bugs lethal. That is a bad end for both host and pathogen in a small roving, band because when the people die, the bugs are left with nowhere to go, and they die, too. The genes that make germs good at suicide don't tend to last very long.

All of this changed roughly 12,000 years ago at the dawn of agriculture and human civilization and the rise in population density. In large, concentrated human populations, bugs can get away with being lethal. Smallpox, bubonic plague and influenza can kill huge numbers of us and still thrive because there are huge numbers of us to kill. In a population of billions, the death of millions is inconsequential - except, of course, to the millions concerned. In a population of billions of hosts, small pox, influenza, measles, mumps, rubella and polio can wreak havoc and flourish just the same.

What this all means is that arguments for an "au naturel" approach to our concourse with pathogens are, in a word, nonsense. A native relationship with microorganisms is an "in-for-a-penny-in-for-a-pound" proposition. We can't possibly go native without going back to the conditions of our hunter-gatherer ancestry. There is nothing native about a human population in excess of 7 billion.

In modern context, the evidence in support of vaccines is overwhelming. We have eradicated smallpox and come close to doing the same with polio. Those inclined to be blas? about these stunning public health advances are limited to the beneficiaries of them. Populations subject to the ravages of smallpox and polio fully appreciate what it means to be rid of them. That the debunking of any meaningful link between vaccination and autism falls on deaf ears does nothing to alter the epidemiologic truth. Immunization does not cause autism.

[Read: Autism and Childbirth: A Link?]

The flu vaccine is far from perfect. It can fail to prevent flu, and there can be rare complications. But it usually does prevent flu, and complications of the flu itself are more common by literal orders of magnitude. I do understand the reasons for reticence about immunization in general and flu immunization in particular. For any vaccine to do us any good, we need to get it while feeling fine. This is quite different from, say, an operation that is much more dangerous - but easily justified by the obviously hemorrhaging bullet hole, plugged-up gall bladder or occluded arteries. Convinced as I am of the benefits of immunization, I feel a momentary hesitation each year myself. But I get over it, and roll up my sleeve. I recommend you do the same.

If I've failed to convince you, or you get the vaccine too late to prevent influenza, there is medication available to shorten the course of illness and reduce the risk of complications. If you develop fever, headache, cough and/or body aches, contact your doctor to find out if you are a candidate. The CDC provides very helpful information about antiviral medications online.

When confronting flu, as ever, lifestyle makes for very powerful medicine. Smokers are far more vulnerable to flu and flu complications than non-smokers, in case we needed yet another reason to avoid the scourge of tobacco.

Eating optimally, being physically active and controlling our weight all have strong, favorable influences on immune system function. Sleeping enough and well and managing stress effectively also exert strong, beneficial influences on immune responses. Certain nutrients are also very important, notably vitamin A, vitamin D and zinc. Food is generally the best source of nutrients, but vitamin D supplementation is usually required to maintain blood levels during winter months. I recommend 1000 IU to 2000 IU daily to most of my patients and take that dose myself.

[Read: Steer Clear of the Cold: Foods That Boost Your Immune System.]

Exposure to the flu does not mean infection; a strong immune system may prevent the virus from getting established.

The flu ranks among the great infectious disease killers in human history and is an unusually wily germ into the bargain. It deserves our respect. We should respect it by defending ourselves and loved ones against it.

This being my first column of 2014, I'll take the opportunity to wish you and all who matter to you good health and great fortune in the New Year. Permit to suggest, though, that you not just wish for such things - but work toward them. The flu, like fortune, will favor the prepared.

[Read: The Path to Health: Willpower and Skill Power.]

Hungry for more? Write to eatandrun@usnews.com with your questions, concerns, and feedback.

David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011 and is president-elect of the American College of Lifestyle Medicine. He is the author of "Disease Proof: The Remarkable Truth About What Makes Us Well."