Influenza Update: 2014 – 2015 flu season changes

~ by James M. Wilson V, MD

Media reports have recently focused on CDC statements indicating we are having a “severe” season of influenza. This concern was initially driven by the discovery of a vaccine mismatch involving the type A/H3N2 component of the vaccine. We have discussed this issue extensively in previous posts here on SERMO and emphasized the following points:

• The phrase “vaccine mismatch” does not guarantee a severe season of influenza. The current 2014-15 season is comparable to the activity seen in 2012-13, a non-mismatch season.
  The main exception of concern is the elderly, which will be discussed in this post.
• That vaccine mismatch associated with a dominant A/H3N2 season is common and not unexpected.

The term “severe” is imprecise. It is as imprecise as the terms pandemic, epidemic, and outbreak in today’s public health discourse. At the Ascel Bio National Infectious Disease Forecast Center, we use terms that describe the level of socio-economic disruption to a community that are captured in the Infectious Disease Impact Scale (IDIS).

Figure 1. The Infectious Disease Impact Scale (IDIS). From top to bottom, this scale is a heuristic model that describes the transition points of socio-economic disruption experienced by a community in the context of an infectious disease outbreak or epidemic.

We use the IDIS to provide a “bottom line,” high level view of infectious disease activity and are using this analytic tool to describe the effect of Ebola on the core involved countries in West Africa:

 Figure 2. Signature tracing of socio-economic disruption caused by Ebola over time in Sierra Leone. The X axis is the day, going back to the beginning of the disaster. Ebola has generated persistent IDIS Cat 6 conditions for months in Sierra Leone.

The best analogy for the IDIS is a comparison to the Fujita scale, which is a heuristic model used to describe the magnitude and potential impact of tornadoes. The IDIS is an important tool for our analysts because an “epidemic” of disease in one country may be described an “epidemic” in another- but be associated with completely different IDIS categorizations that relate to that country’s medical infrastructure and response capacity.

Currently in the United States, we have yet to document a community experiencing more than IDIS Category 2 conditions for influenza. Despite media attention, we are not observing unusual socio-economic disruption levels.

There are reasons for these observations. First, let’s take a look at the current surveillance data from this year’s influenza activity.

From a pediatric (i.e. birth to 18 years old) perspective, we are seeing a routine season of influenza in our younger birth to 4 year old children, but high activity in the 5-17 year old age group.

 Figure 3. Influenza hospitalizations in the pediatric age group. The Y axis on the left corresponds with
incidence for prior seasons except the pandemic season of 2009-10, where children were severely effected. Pandemic incidence is read on the right hand Y axis associated with the orange trend line. [Data source: CDC FluView]

 

Figure 4. Pediatric mortality due to influenza. This is the true bottom line for severity from a clinical perspective. We are not seeing an unusual level of mortality so far in the pediatric patient population compare to prior seasons. The main caveat is mortality data is delayed sometimes by weeks, so a final assessment at the conclusion of the season (i.e. in the summer) will be required. [Data source: CDC FluView]

 From the perspective of our working age group, which is responsible for maintaining economic throughput for the nation, this continues to be a routine influenza season.

Figure 5. Influenza hospitalizations in the working age group. In this age group, the 2009-10 pandemic season’s impact for the end of December / early January time period was comparable to a routine influenza season. This year’s influenza activity level is routine. [Data source: CDC FluView]

The elderly, however, have been hit hard by this season’s influenza, and this is the key observation for this season that has been called “severe.”

 Figure 6. Influenza hospitalizations in older adults and the elderly. In this age group, the 2009-10 pandemic season was not severe at the end of December / early January. What is notable is the 2014-15 season is associated with the highest level of hospitalizations in this age groups since before the pandemic. [Data source: CDC FluView]

 From the perspective of overall mortality due to pneumonia and influenza, this season is routine, however the data is still being compiled and will require re-examination in early summer.

Figure 7. Overall mortality due to pneumonia and influenza. So far, mortality appears to be comparable to all prior seasons of influenza. Caveat: there are inherent time delays in reporting of mortality data, so this information should be interpreted with that in mind. [Data source: CDC FluView]

In summary, we observe the following:

• The current influenza season overall is not “severe” and is comparable to the prior two years of seasonal activity. We observe no higher socio-economic disruption than IDIS Category 2 (non-crisis) conditions.
• For older adults and the elderly, this is a severe season.

One last point of importance: the concern about a “mismatched” vaccine. The majority of America, including its physicians appear to hold a belief that the vaccine is “useless” because mismatch has occurred. Yet both WHO and CDC continue to recommend the use of the vaccine. It is critical to keep in mind the following key points:

• The vaccine, while mismatched, is not fully. In other words, there remains a probability the vaccine will keep an individual out of the ICU or from dying.
• Patients should question a physician who does not offer the influenza vaccine, despite the mismatch. Physicians should offer the vaccine to patients regardless of the observation of a mismatch. If anything, observation of a “mismatch” is a major warning to society to encourage even broader vaccination than is normally done.
• Tamiflu may or may not save your life if you are hospitalized with influenza. Tamiflu is considered by the majority of physicians to be of questionable value when a patient has been ill for several days and later hospitalized. The bottom line is don’t depend on Tamiflu to save your life if you choose not to vaccinate.

Biography

Dr. James Wilson, a pediatrician and infectious disease expert with AscelBio, he is a frequent contributor to the SERMO blog.

Season flu and it’s movements in the US are discussed frequently inside SERMO.  If you’re an MD or DO please join us for the latest news shared by your peers.