Effect Measure

It is becoming conventional wisdom that the 2009 H1N1 pandemic was not as severe as a bad seasonal flu year. That might be true, although I don’t find it much comfort because a bad seasonal flu year is no less bad for being more familiar. But I am not yet willing to assent to the conventional wisdom yet. I don’t think we have had sufficient time to collate all the information that would enable us to make that kind of judgment, which sometimes takes years to evaluate. However bad it was or wasn’t, the pandemic flu strain could kill you just as dead as any other flu. CDC has just released updated information on the risk factors that seem to make it more likely you will wind up severely ill and hospitalized. It confirms what we knew, that certain pre-existing medical conditions up the risk substantially and some of them are extremely common. The analysis was done for both children and for adults, and there are similarities and differences.

The data come primarily from the Emerging Infections Program (EIP), which we’ve featured quite often here (for one example, see here). EIP counts laboratory confirmed cases of influenza in children and adults in 60 plus counties that include 12 metropolitan areas in 10 states (San Francisco CA, Denver CO, New Haven CT, Atlanta GA, Baltimore MD, Minneapolis/St. Paul MN, Albuquerque NM, Las Cruces, NM, Albany NY, Rochester NY, Portland OR, and Nashville TN). The surveillance system uses laboratory and admission databases and infection control logs generated by routine hospital operations. A special compilation of underlying medical conditions is then obtained by chart review.

The results for EIP data collected between April 15, 2009 (when the first swine flu cases in the US were detected) and February 16, 2010 and show that 85% of adults hospitalized with 2009 pandemic H1N1 flu and 58% of children had underlying medical conditions. This means that 1 in 7 flu hospitalizations were healthy adults but almost half of all children. The idea that the only kids who went sour with flu were the chronically ill is unfounded. And for both adults and children the most common “underlying medical condition” is quite common: asthma. We’re not talking about uncontrolled ashtma. Just having asthma and having it mentioned in the medical record is enough to put you in the “underlying medical condition” category. And 9% of the hospitalizations were pregnant women.

Here are the charts for adults and children. Note that a person can have more than one condition, so the percentages add up to over 100%:

i-3b5612fdbd3d956770b1385bebadf685-eip_underlying_conditions_grapha.jpg

i-68896ea898ee0d4a9ea9743fb8f4fdbf-eip_underlying_conditions_graphb.jpg

CDC

WHO has not declared the end of the pandemic, since community transmission is still occurring in West Africa and perhaps elsewhere. Moreover the flu season will be ramping up again in the Southern hemisphere and no one really knows what form it will take. We are in uncharted territory in many ways.

So far there has been no third wave nor any sign of the former seasonal influenza strains. Let’s hope that’s the way it will stay, at least for this winter-spring season. If it does, that will be good but we won’t know why it came out that way. Just that it did.

No one who knows flu is particularly surprised because no one who knows flu would or should be surprised by however it comes out. With flu, it seems almost anything is possible.

Comments

#1 pft
February 26, 2010

Flu is like climate, man does not really understand it. So when flu comes, or climate changes, man best just try to adapt to it and not waste too much time and money preventing what it does not understand (trying to prevent what you don’t understand could cause unintended consequences). With flu, vaccines may help those who choose to get them, but they can typically only be developed after the initial outbreak, and are not without some adverse outcomes.

That new strains of influenza affect healthy adult/children more severely than older strains to which they have a partial immunity is hardly unexpected. After this season, most of those healthy people which have been affected, even if they had few symptoms, will also have some immunity to future outbreaks. Natural immunity is a vaccine makers nightmare of course. LOL.

Of course, 1918 must be kept in mind. The initial wave was also mild, but subsequent waves more severe. Those infected in the first wave were believed to have had some partial immunity to the more severe 2nd and 3rd waves. This was of course in a day in which many adults and childrens immune symptoms were compromised by WW I, and the lack of antibiotics meant many died due to bacterial pneumonia. Also, the conditions in our inner cities were deplorable, especially areas where poor immigrants lived. Such a pandemic might not be possible again outside 3rd world conditions (keep an eye on Haiti BTW). However, nobody knows for sure.
#2 Alex
February 26, 2010

@pft: We’re not gonna start the anti-vaccine conspiracy theories again right?

“and are not without some adverse outcomes”
>> Only one which caused trouble was the 1976 one for flu and even then it’s not clear if it was really the vaccine. Public health authorities stopped giving the vaccine for fear that that was the reason (precautionary principle) but anti-vaxxers misrepresented what happened and took that event as evidence that vaccines cause trouble.

“Natural immunity is a vaccine makers nightmare of course.”
>> Exactly the opposite.
1) Natural immunity requires that the infected person survives the disease, isn’t necessarily acquired after the fight and doesn’t last forever.
2) If the person is not vaccine-immune and gets sick, Big Pharma makes much more money off of them because the sick have to buy cough syrup and other medications which are much more expensive than a flu shot (which is about 10$).
#3 cmc
February 26, 2010

I am not an immunologist, but would a stratified random sample of age groups by vaccine status, with immune titre for HiN1 (and seasonal just to be sure)give us a good benchmark of what happened this year (vaccine effectivenss and herd immunity), and as a baseline for progressive annual comparisons?

If we had a good sample frame in place (an unmet public health priority), the max number of participants could be about 20,000 ((~1200 per age group x 8 decade groups) x Y/N vaccination status) but a sampling statistician could create a strategy requiring fewer.

Alex, wild-type immunity is incomplete? Due to variance in the load of virus units? Or due to variable strength within the virus unit? Or other factor? I understand that host survival is an invalid criterion for immunity, and the distribution of effective titre levels is lower . . . ??
#4 Opitmal
February 27, 2010

Would one of the Revere people please speak to the antiviral resistance issue.. especially as it regards Peramivir high peak plasma level and half life? Compare to Relenza relatively low levels?

Thx
J
#5 davidp
March 1, 2010

What are the frequencies of asthma and diabetes in the general population in the sampled areas ? If they are comprable to the ‘flu hospitalisation rate then the “underlying condition” is not significant.
#6 raven
March 1, 2010

It is becoming conventional wisdom that the 2009 H1N1 pandemic was not as severe as a bad seasonal flu year.

Is that right? I ran some numbers a while ago. The US pediatric deaths were 2-4 X average years. And use this as a indication of how severe a flu season is, since actual pediatric deaths are closely reported.

It is late here, not going to chase the numbers down tonight.

Still, it wasn’t 1918. Opinions differ on how much our advanced science and the frantic running around had on the possible course of the epidemic. My own feeling is a lot. In some countries without our medical infrastructure, pediatric deaths were much higher than usual.
#7 raven
March 1, 2010

from last year:

* Did you know that criminal charges are being filed in multiple countries as well as
with the FBI against the WHO / UN for conspiring to decimate the human population
with a reverse engineered virus concoction to be delivered via a global mass
mandatory vaccination program in the fall of 2009? http:// tinyurl.com/journalist-against-who

* Did you know that the world’s governments including the US have signed over their
sovereignty to this same WHO in a time of ‘crisis’? And are you aware that the US
and Europe fully intend to militarily enforce the lethal injections to be mandated this
fall? http://www. prisonplanet.com/military-to-work-with-fema-during-swine-flu-outbreak.html

Well talk about wrong. According to the usual wingnuts, the flu vaccine was going to kill billions of people in a UN/Rockefeller/Illuminati/Obama world population reduction program. Resistors were to be sent to the FEMA concentration camps in the midwest USA.

I’m sure they are onto the next conspiracy fantasy by now.
Universal health care is a commie plot or some such.
#8 Kathy
March 1, 2010

Wow, sobering. Having had type 1 diabetes for 27 years, I got my flu shots early this year. Didn’t get either flu (knock on wood). Glad I subjected myself to such a dangerous public health menace–vaccination!
#9 Paula
March 1, 2010

Of course we all made sure we and our loved ones got, in our turn, the new flu vaccine, we urged the making of more vaccine, we chuckled just a bit about “anti-vaccine nuts,” and I certainly do not argue now against this. Yet, nearly three months into a local struggle to protect my and others’ homes and health from the very real danger of serious noise and infra-noise from a proposed set of wind turbines, and having on numerous occasion been called an “anti-green nut” (and various variations thereon) for doing so (as if everyone’s response to noises were the same, and as if in this particular case industry “research” alone could adequately be trusted), I really feel for anyone whose views are being twisted and dismissed. (Not sure if this applies to anti-vacciners, who are after all endangering people, including often their kids.)
#10 kim
March 5, 2010

Revere wrote: “So far there has been no third wave nor any sign of the former seasonal influenza strains.”

Did seasonal influenza make any appearance in the US from autumn 2009 to the present? In 2009 pandemic H1N1 had completely replaced the expected seasonal flu. Has that situation continued throughout 2010?

If a usually healthy individual developed a URI in 2010 that was diagnosed as viral in nature (by symptoms, not by testing), would it be reasonable to assume that the person had contracted H1N1 and became a part of the herd immunity?
#11 revere
March 6, 2010

kim; As of March 5, there is no sign of the previous seasonal flu A H1N1 or H3N2. There is some low level influenza B activity. As for your second question, the answer is “no.” There are many viruses that cause URI that aren’t influenza.