Effect Measure

What are we to make of the swine flu pandemic? The only thing I feel confident about is that it will be some time before we really know. A great deal of data and experience was gained in the year since the pandemic H1N1 took everyone by surprise but it will be a while before we can harvest all of it. Meanwhile I can say things were better than we thought they might be and certainly better than everyone’s worst fears, but how much better — better, how bad — they were we just don’t know. It was a very good year for people in my age category (over 65) as for reasons now becoming a bit clearer we were least susceptible. In ordinary flu years we are the most susceptible and we die in large numbers. This last year it was the young most at risk. The numbers of flu deaths overall don’t tell the complete story, nor does the fact that many hospitals seemed able to cope. In Australia and New Zealand in the southern hemisphere who got the first full flu season with the virus, they almost didn’t cope:

Intensive care units in New Zealand and Australia came close to turning seriously ill patients away during last year’s swine flu pandemic, doctors say.

A year after the first cases of the virus were reported, researchers said it put 12 times the usual number of flu patients into intensive care in both countries last winter.

[snip]

Although the virus was a mild disease for most people, many with more serious symptoms needed critical care, Sydney-based intensive care specialist Ian Seppelt said.

“Most years, in that three-month period there are about 60 to 70 cases of viral pneumonitis in all [New Zealand and Australian] units.”

Last year there were 856 cases – 119 in New Zealand – with 760 of those attributed to swine flu, he said.

[snip]

“If we had had any greater activity of that virus we would not have been able to offer that service [to everyone].”

Unlike normal flu seasons, it was predominantly younger people with no underlying symptoms who needed intensive care, Dr Seppelt said.

Wellington Hospital intensive care unit director Peter Hicks said he had “never seen anything like it before where we’ve had a disease that’s so significantly impacted all the intensive care services across the two countries”.

New Zealand hospitals had not had to turn people away from intensive care units but “it got close”. (Kate Newton, The Dominion Post)

So instead of old people in intensive care it was a lot more young people. “A lot more” meaning an unprecedented number. When put that way, the swine flu episode doesn’t sound quite so benign. Already analyses are showing that in terms of lives cut short prematurely, the 2009 pandemic was on the order of severity of the last pandemic in 1968 (full text of paper here). This is despite many medical advances in the interim.

How it will turn out in the fullness of time we don’t know yet. And there is another flu season starting the southern hemisphere and we will get our usual one next fall and winter. What either will look like we also don’t know. The betting is that pandemic H1N1 has replaced the previous seasonal H1N1 and will become the “new normal,” i.e., the seasonally circulating H1 subtype. For some years yet a good proportion of the population still does not have natural immunity, although many acquired artificial immunity with the swine flu vaccine. What the impact will be we don’t know, either.

Flu is like that.

Comments

  1. #1 Hand Gel G
    April 26, 2010

    Given the high cost of ICU and HDU it’s not surprising most places do not have much excess capacity at the best of times; let alone in a pandemic.
    In my opinion when an area/country gets close to ‘not coping’ it’s time to invest in extra capacity.
    Sometimes we get lucky and we get a warning – it’s best not to ignore the warnings when we get them.
    We all know it’s a question of ‘when’ rather than ‘if’ we get a pandemic – right now I don’t think there are many places ready for it… and, sadly, I don’t see many places investing to make sure they are ready.

  2. #2 Jody Lanard M.D.
    April 26, 2010

    Revere, to fine tune your comment that “This last year it was the young most at risk:”

    Note that of those younger than 65 who were most at risk, it was 50-64 year olds who were most at risk of death, in terms of deaths per 100,000 persons in that age group.

    Kids 0-4 were most likely to be hospitalized, but least likely to die, in terms of hospitalizations and deaths per 100,000 in that age group.
    Here is a clear CDC graph of U.S. age-specific deaths.
    Here is a clear CDC graph of U.S. age-specific hospitalization rates.

    These graphs represent incomplete interim data, but seem to be the best data available at this time.

  3. #3 revere
    April 26, 2010

    Jody: Thanks. This would seem to make sense as this group shares the mortality susceptibility of the older age group that usually is hit and infection susceptibility of the younger age group. If we had a good fix on risk of infection we might see a different picture. The case fatality rate (CFR) may retain its usual relationship with age but the risk of infection may be very different. For those not familiar with CFR, it is the risk of death GIVEN that you are infected, not just the risk of death per population.

  4. #4 elephantman
    April 26, 2010

    It is interesting that the age specific curves for Australia are quite different from those in the United States.

    Although peak mortality in Australia still occurs within the 50-60 year age cohort, the relative incidence of mortality from pH1n1 among children and adults younger than 35 years of age was very much lower that that recorded in the United States and Mexico.

    Compare CDC data with that from Fig 11 on Page 13 at
    http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/ozflu2009.htm/$File/ozflu-no24-2009.pdf

  5. #5 anon
    April 26, 2010

    the Vibaud et.al paper says:

    > The range of years of life lost estimates includes in its lower part the impact of a typical
    > influenza epidemic dominated by the more virulent A/H3N2 subtype, and the impact of
    > the 1968 pandemic in its upper bound.

    then they give an “upper bound”, which is 6 times higher than the lower bound ! (we don’t know…)

    however, with the CDC-estimates you get:

    > Number of deaths (adjusted to 2000 population): 86000(1968) , 12000(2009)
    > Years of life lost (adjusted to 2000 population): 1693000(1968) , 463300(2009)

    so, writing:

    > Already analyses are showing that in terms of lives cut short prematurely, the 2009 pandemic
    > was on the order of severity of the last pandemic in 1968

    looks a bit biased to me. You have an interest to make it look worse, so you pick what
    you think serves that goal best (upper bound) but make it look as if it were a normal
    estimate. Also unclear what you mean with “lives cut short prematurely”, which
    they say is “years of live lost”

  6. #6 Jody Lanard M.D.
    April 26, 2010

    Revere, you make the very important point that “The case fatality rate (CFR) may retain its usual relationship with age but the risk of infection may be very different.”

    From all available interim data, the pandemic CFR is drastically lower for the 65 and older age group than during H3N2 flu seasons.

    But the Case Attack Rate in that age group does not appear to be lower than during the average flu season. Here are some rough estimated data on pandemic H1N1 Case Attack Rates (and CFR’s as well).

    Estimated case attack rate data:

    From April to Oct 17 2009: (population numbers drawn from U.S. Census Data)
    Estimated case numbers, mid-level range

    Age group…Cases(est)…Population…Case Attack Rate (est)
    0-17…………..8 million……75 million…..10.7%
    18-64………..12 million…..194 million……6.2%
    65+……………2 million……39 million…….5.2%

    From April to March 13 2010:
    Estimated case numbers, mid-level range

    Age group…Cases(est)………………………… Case Attack Rate (est)
    0-17………..19 million (up 237% from Oct 17)…..25%
    18-64……….35 million (up 292% from Oct 17)….18%
    65+…………..6 million (up 300% from Oct 17)….15%

    For all age groups, these attack rates are higher than in the average flu season. CDC states that 5% to 20% of the population gets the flu every year.

    According to the American Academy of Pediatrics’ Committee on Infectious Diseases,

    In community studies, school-aged children have had the highest rates of [seasonal] influenza infection. Prospective surveillance of influenza illness demonstrates annual attack rates of between 15% and 42% in preschool- and school-aged children.

    The CDC mid-level range estimates of case numbers by age group, listed above, suggest that seniors 65 and older had a higher pandemic attack rate than during the average flu season.

    You can use the CDC estimates of age-specific cases and deaths to calculate very rough estimated mid-level range Case Fatality Rates for these three age groups. (And you can see the CDC age-specific death rates (not the same as CFR) for narrower age ranges here):

    Age group……Cases(est)……..Deaths(est)…..Case Fatality Rate(est)
    0-17……………19 million….1270…..0.007%
    18-64…………..35 million….9420…..0.027%
    65+………………6 million….1580…..0.026%

  7. #7 revere
    April 26, 2010

    anon: Bias is in the eyes of the beholder in this case. I provided the link, which you read. The judgement about 1968 is the authors’. OTOH you never miss an opportunity to stick it to us. That seems a bit biased to me.

  8. #8 Anonymous
    April 26, 2010
  9. #9 revere
    April 26, 2010

    Anonymous: Nope. Have only been told it is seasonal flu vaccine.

  10. #10 Magpie
    April 27, 2010

    Most money on a bad batch at the moment. Nation-wide vaccination program, good uptake, but almost* all the cases from one city.

    It was a combination of both seasonals and the New Kid – so three strains at once. But really, that shouldn’t matter. Says my arse.

    * …the “almost” has me confused, but I’ll see what I can find out tonight and let you know.

  11. #11 davidp
    April 27, 2010

    The Australian issue is with young children who received a seasonal flu vaccine targetting:
    – A/California/7/2009 (H1N1) (Swine Flu)
    – A/Perth/16/2009 (H3N2)
    – B/Brisbane/60/2008
    I was vaccinated with an adult dose today.

    It has mostly occurred in the state of Western Australia. About 250 children have reported fever, with 55 serious cases (fever with convulsions or similar). Strangely there seem to have been far fewer cases in children in the East, where 90% of Australia’s population live.

    “Western Australia’s Chief Health Officer, Tarun Weeramanthri, said it was increasingly unlikely a single adverse batch of vaccine was to blame, due to the number and spread of reactions”

    It’s pretty mysterious to me, an ordinary person living in Australia’s East.

  12. #12 Jonathon Singleton
    April 27, 2010

    Thanks David for supplying the details of the new seasonal vaccine combo from CSL… I live in Perth and am watching this issue with similar feelings of, “Huh, what’s going on?”

  13. #13 davidp
    April 27, 2010

    WA is the only Australian state to offer free seasonal flu vaccinations to all children under five. A report from W.A on 23 April has half the febrile convulsions linked (in time) to flu vaccine:

    The Princess Margaret children’s hospital (PMH) had reported 44 children under 10 had presented with febrile convulsions, of which 23 related to the paediatric flu vaccine.
    Of the 23 children, 12 were admitted to hospital.

    Source
    Lots of Australian children were infected with ‘Swine Flu’ last winter – far more than the official statistics showed, because it was usually fairly mild, not needing a doctor. I do not know how prevalent it was in WA. Could previous infection have made them more likely to develop fever after this vaccination ?

  14. #14 anon
    April 30, 2010

    you picked from many available judgements.
    I “stick it” to others too. Usually I’m less likely to post
    about the agreements(which do exist) than the disagreements.
    Agreements needn’t be changed, needn’t be discussed

  15. #15 Ruth S.
    May 1, 2010

    I had this forwarded to me by someone concerned I was going to be ‘risking my life’ my getting my normal flu vaccination this week (which I’ll be doing anyway). I haven’t been able to find out much about the reported increased susceptibility to swine flu if you’ve had the ordinary ‘jab’, and I’m curious about just how strong/weak the link is.

    http://www.foodconsumer.org/newsite/Non-food/Drug/risk_of_swine_flu_0150100835.html

    (On an unrelated note: just how common is lack of vitamin D in the developed world today, anyway? Or is D the new C when it comes to cold & flu fads?)

  16. #16 revere
    May 1, 2010

    Ruth: We discussed this here:

    http://scienceblogs.com/effectmeasure/2010/04/did_getting_vaccinated_with_se.php

    Mercola is a well known crank and anti-vaxer and I wouldn’t believe anything he says. However the issue is a real one.

  17. #17 Ruth S.
    May 1, 2010

    Thankyou! *chuckle* at least it wasn’t the Huffington Post… (Talk about culture shock the first time I got referred to that!) So many dubious ‘news’ stories get hyped, and often finding ‘quick and easy’ refutations or balanced replies takes annoyingly long.

    Appreciate the quick reply, and I’ve sent her the article to read through.

  18. #18 Thermometer
    December 21, 2010

    I think a lot of people are relieved that the swine flu pandemic wasn’t as bad as many expected. Thanks for your take on the matter.

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