Friday, August 28, 2009

H1N1 flu shots

Coming soon to your neighborhood supermarket: An ounce of prevention against H1N1.

More precisely, .0000005 ounce of prevention which is the teensy-weensy amount of killed viral material that scientists from the CDC, National Institutes of Health, and various licensed pharmaceutical companies inserted into syringes as they launched clinical trials of newly manufactured H1V1 vaccine earlier this month. They expect to analyze study results from mid-September to mid-October and then begin the first public immunization programs before Halloween. The trials will provide important information on the vaccine's safety, efficacy, and whether one or two doses are needed to provide optimal protection. (Study results released 9/10/09 indicated that one dose for adults is sufficient.)

We already know that H1N1 influenza, first identified in Mexico in late winter of this year, is the most common cause of flu-related illness throughout the world at this time. While this new viral strain continues to cause low-levels of new cases in all 50 states, it is currently 'widespread' in Maine and Alaska. But the regular flu season has not even started yet, and once the usual seasonal blend of influenzas A and B hits, we can expect a double whammy of flu-driven illness this fall into winter.

Quite a few of you have called our office with logistical questions about how best to protect yourselves and your families against this onslaught of respiratory crud. Here's the latest information:

What can we expect?

We know that H1N1 flu is quite contagious, easily passed person to person via contaminated secretions from coughs and sneezes, and able to survive on surfaces for up to 8 hours. While the initial reports from Mexico were quite disturbing with respect to the severity of illness caused by this strain, the illness lately has been acting a lot like seasonal flu. It does disproportionately affect persons under 60 and and can be unusually virulent in those under 25. Per Dr. Jay Butler of the CDC, "75% of the [H1N1]hospitalizations are in those aged under 49 and 60% of the deaths are in those under age 49." Studies showed that no young adults demonstrated circulating antibodies to H1N1 at the start of this pandemic whereas many older adults apparently encountered a similar influenza variety in the past and were found to have some immunity to this strain.

Experts are unable to estimate the community prevalence of H1N1 as many cases are too mild to come to medical attention. In addition, as H1N1 becomes more prevalent, the CDC no longer recommends that such mild cases be tested to confirm the presence of this specific virus.

As I've mentioned in previously posts, influenza is a tricky and changeable foe which can mutate rapidly. Thus far, thankfully, studies of the virus from recent cases in the southern hemisphere demonstrate no significant genetic change from northern cases investigated earlier this year.

What's the difference between H1N1 and the seasonal flu?

H1N1 is a novel strain originating in swine (but not caused by consumption of pork!) that developed in North American pigs through the mixing in their respiratory tracts of genetic material from swine, human, and avian flus. It is antigenically distinct from seasonal flu which means that its proteins and genetic material are completely different than the ordinary influenza types that circulate each winter season.

Will I need shots for both?

Absolutely. Separate shots will be available for seasonal and H1N1 flu. Preliminary information released in an online version of The New England Journal of Medicine 9/10/09 indicates one dose will be sufficient for adults; the proper dosing for children is not yet available.

The seasonal flu shot and the H1N1 shot can be taken on the same day--but different arms please! The seasonal shot is already available, however, whereas the first H1N1 vaccines will not be distributed until late October. While the optimal time to receive the seasonal flu shot is October or November to assure that immunity lasts through the entire season, the CDC currently recommends that persons receive the seasonal vaccine as soon as possible to assure that both flu shots can be administered to the largest number of people.

How can I get the H1N1 vaccine?

While the CDC was hopeful that ample vaccine would be available by October, production delays will slow delivery of adequate vaccine until later on in the year. For this reason, certain groups have been assigned top priority for the first wave of vaccinations, chosen due to their risk for more serious disease. These include:
  • Pregnant women
  • Persons who live with or provide care for infants aged <6>
  • Health-care and emergency medical services personnel with direct patient contact
  • Children aged 6 months--4 years, and
  • Children and teens aged 5--18 years who have high risk medical conditions

What about college-aged children?

The CDC and universities are implementing various programs to limit the spread of H1N1 disease on campus. Some Colorado schools will offer alternative housing for dorm residents whose roommates become ill.

Stay tuned for up-to-date information on the use of anti-viral medications such as Tamiflu for H1N1 prevention and treatment.

Tuesday, August 25, 2009

Triple Reassortment Swine Influenza*

*aka Triple Reassortant Swine Influenza

"Six of the eight genetic segments of this virus strain are purely swine flu and the other two segments are bird and human, but have lived in swine for the past decade."
---Raul Rabadan, PhD, computational biologist at Columbia University

And that is why pigs are dubbed "mixing bowls" for influenza viruses. While humans are susceptible to human influenza viruses and somewhat less so to the swine varieties (at least up until now), our airways don't provide particularly good handholds for those influenza subtypes that seek out birds. Pigs, on the other hand, have receptors on the surfaces of their tracheal cells that welcome strains from all three species. From porcine throats and lungs, therefore, emerge new flu varieties with the potential to cause dangerous human disease.

These new flus are called triple-reassortment swine influenza A viruses as they contain genetic material from bird, human, and pig influenza viruses. Until recently, the pigs of North America kept their flu to themselves with sporadic reports of human infections generally limited to those most exposed to pigs in their daily work. Now, however, with another flip of their surface proteins--and flu viruses reproducing every 8 hours have 3 opportunities per day to mix, match, and mutate their DNA in a promiscuous sort of way--the little swinish devils have brought these reassorted flus to human airways. Furthermore, this newest genetic triple threat passes easily from one infected human to another.

With all this mating and mutating, therefore, epidemiologists are finding it hard to predict what's in store as the swine flu (and it is a swine flu no matter what it's called, passed at first from live pigs not pork meat) makes it way back to the Northern hemisphere big time. Fortunately, vaccine production is underway, and immunization programs should begin next month. More on that soon.

Saturday, August 01, 2009

What's a Phase 6 pandemic?


Grim?!? Whoa, that's a pretty strong word. In this weekly flu update, we'll check out the ease with which the H1N1 (formerly known as swine) flu spreads from person to person, and why the CDC is hoping for a timely vaccine against the virus.

What's a Phase 6 pandemic?

Sounds serious, and indeed it is insofar as it speaks of the ease with which this little hummer spreads from one human to the next.

The World Health Organization (WHO) has developed a 6-tiered approach that classifies the worldwide threat from strains of animal influenza newly arrived in human airways. Each higher level indicates an increased penetrance of the virus into human populations. By Phase 6--the current global level of the H1N1 flu--the virus has shifted into a lean, mean, human-to-human infecting machine in at least two countries of one WHO region and with spread detected in at least one country of a different region. This particular influenza virus, therefore, reached Phase 5 once it spread from person to person in Mexico and the United States; its subsequent spring '09 appearance in the Southern hemisphere then raised the threat to level 6.

Experts agree so far that this variety of influenza has a 'substantially higher' rate of transmissibility than the usual seasonal flu although this in itself does not mean that it's more lethal.

So what's transmissibility and what's the H1N1 score?

Influenza is quite contagious as it thrives in infected respiratory secretions and effectively spreads those viral laden droplets into the environment via juicy sneezes and coughs. The smaller the droplet, the longer it floats through the air and the further it penetrates into the airway of the unlucky recipient who inhales it. If the virus is novel--meaning that large portions of the population have never encountered this particular bug before--the risk of contagion is even higher.

Epidemiologists express transmissibility as reproductive number (R0 or R-zero) which is the number of cases caused by one infected person. If the R0 is less than one, the disease fades away, whereas rising R0 numbers mean that the spread of the disease is increasingly harder to contain. Experts think that an R0 more than 2 renders such measures as closing schools and screening visitors from other countries for signs of the disease as virtually useless.

So what's the R0 of H1N1? Compared to the seasonal flu with an average R0 of 1.3, estimates for H1N1 vary between 1.3 to more than 2. Calculating an accurate R0 for novel H1N1 flu is very complicated considering the many unknowns about this pandemic such as the incubation time and the percentage of cases mild enough to escape official notice. But we must assume that H1N1 is sporting a fairly robust R0 considering its current worldwide status, and, for that reason, we desperately need a vaccine to slow the spread of infection.

Upcoming info

The important thing in containing this pandemic, therefore, is the development and widespread use of an effective vaccine. More on that subject next week.