# 5900
Since 90% of the world’s population resides in the northern hemisphere and influenza-like-illnesses are primarily a winter phenomenon, it stands to reason that the months from October through April are usually the busiest for flu-related stories.
The exception, of course, was the summer of 2009 when a novel H1N1 virus appeared in the spring, and spread globally sparking a pandemic.
Given the unpredictability of flu, I find it unwise to make predictions about the flu season ahead, but we can discuss some of the things we will be looking for in the months ahead.
AFD stands for Avian Flu Diary, and so we’ll certainly be watching for signs that the H5N1 virus has mutated, is infecting humans in countries where it is endemic, or is spreading to other regions.
As the chart below indicates, over the past 8 years reported human infection from the bird flu virus peak between December and March of every year.
Source: FAO-OIE-WHO Technical Update Sept 2011
Fortunately, the H5N1 virus remains primarily a threat to birds, and has yet to adapt well to human physiology. It is difficult to catch, and even more difficult to pass on to others.
The concern, of course, is that given enough time and opportunities, it could mutate into a human-adapted pathogen and potentially spark a pandemic.
This year there are increased concerns over a new clade (2.3.2.1) of the H5N1 virus (see FAO Warns On Bird Flu).
While this new clade hasn’t demonstrated any increased risk to human health, it differs antigenically from the poultry vaccines currently being used in many Asian countries, sparking concerns that a new wave of bird flu may spread through poultry this winter.
Since more poultry infections equals more human exposures, we will be watching this story closely.
H5N1 isn’t the only avian influenza virus out there, and in recent years the H9N2 virus – which is rife in some Asian countries – has been reported in a small number of human infections.
While the H9N2 virus generally produces mild symptoms, that could change as it mutates, or if it reassorts with other viruses. Exactly how common human infection really is with this virus is unknown, since testing is rarely done in the countries where it is most commonly found.
Beyond these two avian front runners, we’ve also seen sporadic human infections with H7s and H11 viruses as well. While their pandemic potential is low, it is not zero.
And since we’re talking about the more exotic flu strains, there are also the swine influenzas to consider. As we saw in 2009, a humanized novel flu doesn’t have to emerge from an avian source.
Over the past 5 years about 2 dozen human cases of (non 2009 H1N1) swine flu have been detected in the United States. Earlier cases were primarily trH1N1 (triple reassortant), while trH3N2 infections have recently emerged.
In August of this year, 4 cases resulting from a reassorted H3N2 swine virus (with a gene borrowed from the 2009 H1N1) showed up in Indiana (1) and Pennsylvania (3) prompting an epidemiological investigation (see CDC Update On Recent Novel Swine Flu Cases).
As I wrote in What Lies Beneath, it likely that very limited human-to-human transmission of this virus may have occurred, but the virus does not appear capable of sustained and efficient transmission among humans at this time.
The concern, of course, is that could change - and so along with avian flu - we’ll be watching for signs of swine flu development as well.
Of course, it doesn’t require an outbreak of a novel influenza strain to make for an interesting flu season. We’ve plenty of already humanized flu viruses out there to keep an eye on.
As the chart above shows, influenza viruses emerge, often dominate for years, and then are replaced by newer strains.
Sometimes new and improved versions of older strains return after years of absence.
Going into this year’s flu season we’ve 2 influenza A viruses jostling for position; the 2009 H1N1 virus – which dominated much of Europe last year, and the H3N2 virus – which made up the largest portion of North America’s last flu season.
Each of these influenza A viruses has branched into several different genetic groupings, and so we’ll be watching for genetic changes that might signify a change in virulence or affect vaccine effectiveness (see ECDC: Influenza Virus Characterization Aug-Sept).
Often mentioned is the `Norway’ or D222G/N (D225G/N in influenza H3 Numbering) mutation which was first linked to more severe disease by Norwegian Scientists in late 2009. The jury is still out on whether this constitutes a serious threat (see Eurosurveillance: Debating The D222G/N Mutation In H1N1), but it is something that scientists continue to monitor.
Another concern is the potential for these seasonal flu viruses to develop resistance to the most commonly prescribed antiviral – oseltamivir (Tamiflu ®). As we saw over the summer, Australia reported an unusual cluster of resistant H1N1 viruses exhibiting the H275Y mutation (see Australia Reports Cluster Of Antiviral Resistant H1N1).
So far, globally, resistance to these antivirals has only run about 1%-2%. But as we saw in 2008 with the old seasonal H1N1 virus, that can change rapidly.
We’ve also two Influenza B viruses out there as well.
The Victoria lineage of Influenza B has been dominant the last 3 years around the world, but over the past year China has been reporting cases from the Yamagata lineage. While the betting is still on the Victoria strain, we’ll have to see which one becomes king of the viral mountain over the next 6 months.
This year’s flu vaccine provides coverage for:
– an A/California/7/2009 (H1N1)pdm09-like virus;
– an A/Perth/16/2009 (H3N2)-like virus;
– a B/Brisbane/60/2008-like virus.
And so far, this formulation appears poised to provide good protection against the majority of the influenza viruses currently circulating.
Making getting the flu shot a good bet this year.
There are, of course, non-influenza respiratory viruses out there that are not covered by the flu vaccine. Most are mild, but some can produce serious illness.
ILIs or Influenza-Like Illnesses, like adenovirus, parainfluenza, rhinovirus and others are often indistinguishable from influenza without laboratory tests.
Which makes flu hygiene; hand washing, covering coughs and sneezes, and staying home if you are sick imperative, even if you got the flu vaccine this year.
This year, we’ll also be watching to see if more cases of HEV68 – or Human Enterovirus 68 – turn up.
As we saw in MMWR: Clusters Of HEV68 Respiratory Infections 2008-2010, this is a newly identified respiratory virus that has caused several small clusters of serious illness around the world.
And there are literally hundreds of other respiratory viruses out there, all of which are constantly evolving, including:
- metapneumovirus
- parainfluenzavirus
- coronaviruses
- respiratory syncytial virus (RSV)
- adenoviruses
- enteroviruses
- Rhinoviruses (Common cold)
For more on these non-flu viruses I invite you to read Hundreds Of Ways To Spell “I-L-I”.
While I can’t predict what will come down the influenza highway over the next six months, I’m fairly confident that there will be plenty to talk about, and perhaps even a few surprises along the way.
Stay tuned.
