Effect Measure

Thanksgiving and swine flu

In the US we are about to embark on the Thanksgiving holiday, a 4 day period where families get together for a celebratory meal (at least celebratory unless you are one of the original inhabitants of the continent). There is lots of intergenerational visiting (grandparents to great grandchildren and lots of mingling of people from disparate geographic areas). In the midst of a swine flu pandemic, the obvious question is the epidemiologic implications. Ordinarily there is some effect. Ordinarily.

Thanksgiving is typically followed by at least a modest bump in early seasonal flu cases, according to reports from the past few years. But this, of course, is not a typical year. Swine flu is a new virus that accounts for nearly all flu cases right now. (AP via MSNBC)

Not a typical year indeed. We’ve already had as much or more flu at a time by which we usually have recorded little flu, although the flu is in a portion of the population unused to bearing the brunt. So what are the issues here? We’ve already mentioned some of them.

Thanksgiving festivities produce two things of epidemiological import. There are increased close contacts between different age groups (for example elementary, highschool and college age and the over 65 age group); and close personal contacts between people from widely separated geographic areas. It’s a heady mix. December is the time when seasonal flu starts, slowly at first, then picking up steam in January and February. But this year we’ve already had a whole flu season (and more), although the usual victims (old folks like me) have so far been spared the worst. Will it now be our turn, falling prey as we usually do to seasonal flu? Or has the new kid on the block, swine flu, in some way we don’t quite understand, “crowded out” the usual residents? We don’t know yet.

There’s also a new and completely different mix of the susceptible and immune in the population, a vaccination campaign targeting younger populations just starting to get underway, weather turning colder (which increases flu in ways we don’t understand) and a major economic recession that is affecting habits, living patterns and perhaps susceptibilities in unknown ways. The dynamics of seasonal flu — how the disease unfolds in space in time — still isn’t understood and now we have a completely novel situation: not only the aforementioned factors, but possibly four flu viruses (swine flu, two seasonal influenza A subtypes and influenza B) all circulating — maybe — along with the usual other respiratory viruses (respiratory syncytial and rhinoviruses chief among them).

What will be the result? We’re going to find out soon.


  1. #1 stefano
    November 25, 2009

    In all countries of the south emisphere new virus has crowded out seasonal one. In China last reports say h1n1 is 90% of circulating viruses ( at the beginning it was 50%)
    In all previous pandemics, new virus has totally replaced old types. I believe it is more likely a new wave of h1N1 in the colder months. What do you think?
    thank’ you

  2. #2 Bob
    November 25, 2009

    In addition, it’s Hajj time, and 3,000,000 or so Muslim pilgrims from all over the world are coming together to pray in Mecca. By the end of this week, most will be on their way back home. The next couple of weeks could prove VERY interesting.

  3. #3 iljitsch
    November 25, 2009

    If there’s 10 times as much flu and 90% of that is the swine flu, the swine flu hasn’t replaced the seasonal flu at all, and in that case there’s no reason to think that the previous seasonal strains will be gone from now on, like what tended to happen with previous pandemics.

    It’s probably not 10 times as much as in regular years, though, so there is probably a reduction in seasonal flu cases in absolute numbers.

  4. #4 Zachary
    November 25, 2009

    In the US, where the pandemic got started earlier, the figure seems to be closer to 99.9%; seasonal flu has apparently been pretty well displaced. So swine flu could be displacing seasonal flu in China as well — just wait and see if the figures continue to rise.

  5. #5 Rosie Redfield
    November 25, 2009

    Do we have any models for how the H1N1 strain of flu might ‘crowd out’ the seasonal strain? This would make sense if infection with one strain conferred immunity to the other, but that’s not the case here, right?

  6. #6 revere
    November 25, 2009

    The mechanism of “crowding out” is unknown. We discussed it a bit here. stefano, you are correct for the pandemic years but in 1977 H1N1 started co-circulating with H3N2 so we know it can happen. And the pool of susceptibles seems different this year (young versus old). Seasonal flu hits the old hardest. So I’m not willing to make any predictions.

  7. #7 Curious
    November 25, 2009

    That is, unless, everyone already got sick in the first wave! Four of the five young cousins coming to our dinner (two of them my own children) got H1N1 in October or November. The fifth has had the first half of the vaccine.

    I can’t seem to convince their grandparents — my parents and stepparents — to get the H1N1 shot. My mom is 64 with other health issues, but seems to believe that she’s immune due to media reports and that it’s her moral responsibility to opt out. Same with my dad. I’m thankful that there’s little risk of spreading at least that flu among our family this Thanksgiving, but someone is always sick with SOMETHING, so we’ll see.

    Happy Thanksgiving — thanks again for all the work you do.

  8. #8 stefano
    November 25, 2009

    1977 was not a real pandemia. The virus probably escaped from a laboratory ( In USSR ?) and the strain was a descendent of spanish virus of 1950. In 1977 only very young people fell sick, becouse people older than 20 were immunized. For this reasons, I believe, the virus co-circulated with the others seasonal

  9. #9 J
    November 25, 2009

    Your qualifier that Thanksgiving is not a celebratory meal if you’re one of the ‘original inhabitants of America’ is really silly. Who alive today is an ‘original inhabitant of America’? And even if the original Thanksgiving was some kind of catastrophe for the native Americans (which it wasn’t), why shouldn’t its meaning today simply be to be thankful for what one has, regardless of its original connotations?

  10. #10 red rabbit
    November 25, 2009

    Here in rural Ontario we seem to be hitting a bit of a slump (phew). I’m gearing up for the next wave and hoping it doesn’t hit.

    Ou vax programme has gone as follows: early vaccination was the elderly got the seasonal shot and high risk got H1N1. Now we’ve opened both clinics up to all, and we’re pretty busy.

    I’d be willing to wager the immunisation programme has made a significant dent in who will get sick in the coming weeks. It’s been a very good turnout, and I could just kiss all the parents who have come to me with genuine concerns and gone through the information that is available to make the decision whether to get their families immunised (usually yes). It’s been very heartening.

    Oh, and if I was a Native Canadian living in poverty on a reserve, or in jail as an inordinate number are, and with a life expectancy more commonly seen in countries without our resources, I might be wondering what about the Europeans coming to NA I had to be thankful about. I might not. If you really want it to have nothing to do with the pilgrims, well, have fun with that J, because that’s the read it has in the popular media. I’m sure you can change that and I wait with bated breath.

  11. #11 J
    November 26, 2009

    red rabbit,

    There’s no doubt that Europeans committed terrible atrocities against the native inhabitants-just like the native inhabitants committed terrible atrocities on each other. Why should that tarnish a holiday that celebrates precisely cooperation and camaraderie between the Europeans and the natives?

    And I’m sure before the Europeans came the natives lived for 120 years, were in perfect health and lived in a garden paradise. Let’s keep some perspective here.

  12. #12 Interrobang
    November 27, 2009

    And I’m sure before the Europeans came the natives lived for 120 years, were in perfect health and lived in a garden paradise. Let’s keep some perspective here.

    Yes, how about we talk about how the diseases the white colonists brought with them fanned out ahead of their spread, such that new white colonists coming into a previously-uncolonised area where natives had lived would often find their shoes crunching on bone fragments from the density of the dead bodies, or how the population of North America fell by something like 60% because of epidemics brought by Europeans? How’s that for some “perspective”?

    Why don’t you Americans just celebrate Thanksgiving as a harvest festival like we do here in Canada, instead of investing it with some kind of mythical significance that papers over colonialism, imperialism, and genocide? Nobody’s saying that you have to give the holiday up, just stop telling yourself fairy tales about it to make yourselves feel better.

  13. #13 anonymous bloger
    November 27, 2009

    Speaking as someone who has had swine flu (it was quite mild for me), I got it from a music festival as did about 2/3rds of the other people who I attended with. The festival had about 30’000 attendees.

    It will be fascinating to see the effect on spread of things like Thanksgiving and the Hajj. Its just a shame that the statistics aren’t able to capture a better picture of infection patterns.


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