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 The leading web portal for pharmacy resources, news, education and careers November 20, 2017
Pharmacy Choice - Influenza Disease State Management - November 20, 2017

Influenza Disease State Management

Influenza 2015 Update: Matchmaker, matchmaker…what happened?
by Alan P. Agins, Pharmacologist, PhD

Late in 2014, we got news that the most prevalent circulating influenza virus strain this season, H3N2 (A/Switzerland/9715293/2013), was antigenically different from the H3N2 strain that was used to produce this year's vaccine. Depending on the source from who one first heard this news, the sentiments ranged from the cynical: "the vaccine is totally ineffective", doesn't work, is a waste of time and money and this will be a horrendous flu season" to the more optimistic: "the match is still roughly 30-40% for the other circulating H3N2 viruses and essentially a100% match for the circulating H1N1 as well as one of the Influenza B component and near 93% for the other "B" component"…and even if it doesn't prevent the flu, it will most likely reduce the risk and/or severity of flu-related symptoms and complications"

Who's right? The "doom and gloom" people or the "every-cloud-has-a-silver-lining camp"? Well, as everything in life, the truth commonly lies somewhere in between.

First and foremost, there is no question that the influenza vaccine does decrease the chance of getting the flu (CDC, Cochrane Reviews, many others). However, decrease the chance of getting the flu is NOT the same as preventing the flu in everyone. Therein lies the rub, especially for the flu vaccine. It's simply one of the worst in our vaccine arsenal in terms of effectiveness and year-to-year consistency of protection. CDC reports that over the past decade, flu vaccines have ranged in effectiveness from 10% to 60%. On average, that's not much better than flipping a coin in terms of whether it will work or not for any given individual.

According to the CDC, last year's vaccine (considered a good match to the circulating viruses) was in that upper range (50-60%) of effectiveness for children and adults under age 65. For older adults, as always, it was less effective—only about 39%. Put in a different perspective, that meant even with a well matched vaccine, between 40-60% of people receiving it were still at risk for catching the flu anyway. In the end, 2013-2014 was considered a moderate flu season.

As you no doubt know, what seems to makes this year's flu season and vaccine potentially more concerning is that: (1) the mismatch has left the vaccine less than half as effective (23%) as last year's when averaged across all age groups, (2) this current season has been dominated by the more virulent H3N2 viruses which, over the past decade, have been associated with the highest number of hospitalizations and deaths and that, in general, flu vaccine effectiveness is not as high in an H3N2 season as in other seasons and (3) that merely a decade ago there was a "perfect storm" of a H3N2 viral strain and a mismatched vaccine in the 2003-2004 flu season which resulted in nearly 49,000 flu-related deaths (the highest over the past three decades). Was I concerned? Absolutely! I'm on the cusp of entering into that higher risk elderly group.

So, has this been a worse season so far? As of this writing, the CDC flu surveillance website shows this season's peak has passed (it was the last week of December) and that, one measure, the weekly percentage of outpatient visits for Influenza-like illness (ILI), is a little higher (+ 1.4%) compared to last year. This year, however, has followed almost the same exact time course and peak ILI numbers as the 2012-2013 flu season (the two graphs are virtually congruent - remember that term from geometry?). Furthermore, the percentage of all deaths due to pneumonia and influenza have been relatively similar for the past three years and doesn't appear to be higher this year (so far). Of course, influenza-related pneumonia deaths are only a very small percentage of deaths associated with the infection. At any rate, taken together, it would appear on the surface that the mismatched vaccine and the "virulent" H3N2 prevalence have not been as bad as some believed it would be. Maybe the vaccine wasn't totally ineffective. However, there is one statistic that does stand out, laboratory-confirmed hospitalizations. Last year at this time there were overall (newborns thru elderly) about 24 hospitalizations per 100,000 population. Two years ago that number was 33 per 100,000 and this year it is currently 44 per 100,000. As expected, the largest population for flu-related hospitalized is seniors (> 65). Therefore, despite the fact that the percentages of ILIs and deaths due to pneumonia and influenza are about the same for this season and that of two years ago, this current flu season has witnessed almost a 50% (216 per 100,000 vs. 144 per 100,000) increase in the number of hospitalized elderly. As a note, the 2012-2013 season was also predominated by H3N2 viruses while the vaccine was reported to be roughly 56% effective. So, could this year's increase in hospitalizations be totally blamed on the mismatched, 23% effective, vaccine? Or, could it be due to the prevalence of an even more virulent H3N2 virus? Or are both to blame? Who knows! It will be interesting to see, when the mortality statistics are tallied and reported for this flu season if there were truly more deaths. But even then, it will be hard to determine the real culprit - the mismatched vaccine, this particular H3N2 virus or a host of other factors.

So, here's what we know (and don't know): Laboratory tests of vaccine match aren't perfect predictors of what to expect in terms of how well a vaccine will work. A bad match, as determined by current vaccine efficacy and effectiveness methodologies, doesn't necessarily mean it won't work to provide protection. Conversely, even when there's a good match, it doesn't necessarily mean it will be protective for everyone. What is also not known with certainty, even though it's bantered about in the lay and medical literature and by word-of-mouth, is that if the flu vaccine doesn't actually prevent the infection, will it most likely reduce the severity of the flu when one does get it. While there are studies and reports from CDC and others suggesting that this may be the case, it has not been proven absolutely. In fact, there are other studies that state there really isn't any conclusive evidence showing that there is a "lessening" of symptoms or complications regardless of whether the vaccine is a good or bad match.

The bottom line? We really have a lot to do going forward to truly understand how to make a more effective and consistent influenza vaccine, including a potentially major paradigm shift in the technology for their production, as well as how to employ the proper methodologies regarding the measurements of vaccine efficacy and effectiveness as well as cost and sub-population effectiveness. In the meantime, based on safety profile, simplicity, low cost and wide availability, it really comes down to an individual's choice of having some protection, even if it's just 23%. Sometimes, that's the best we've got. But it's better than no protection.

In closing, I'd like to share will share this wonderful analogy in a post by Mark Crislip ( back in November 2014, titled "Why Get A Flu Shot?"…"I think of the flu vaccine like seat belts. No guarantee that you will not die or get injured in an accident, but just as I would prefer to use seat belts in a head-on collision, I prefer to enter the flu season with a vaccination".

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