With the cases in New York I think it is very likely that what we are seeing now is a pandemic. A couple of things. First, the event does not correspond to what has been predicted over the past five years in fundamental respects. The virus emerged not in China, but most probably in California. It was not an avian, but a swine flu virus. And it was not an H5, but an H1 virus.
Second, I have been reading now a couple of times that pandemics are affecting primarily young adults (not children and the elderly as during regular seasonal flu). However, this is true only for the pandemic of 1918, not the pandemics of 1957, 1968, and 1977.
Third, H1N1 viruses already circulate every year in humans during regular seasonal flu, so from a purely technical point of view, the current event cannot be classified as a true pandemic. It is not caused by a new subtype of the influenza virus. What this means is that the category of pandemic influenza will most probably have to be revised in the next few years. As Edwin Kilbourne once put it: “[A]lthough the times may not be out of joint, the viruses are, in the light of current doctrine.†Kilbourne has in fact been arguing for quite some time that the emergence of a pandemic doesn’t necessarily require the circulation of a new subtype. The current event might validate his point, which has not been taken seriously by mainstream expertise.
Fourth, the H1N1 viruses have an interesting story. It is of course the subtype that caused the great pandemic of 1918. The viruses concomitantly infected swine in 1918 and have circulated in the swine population ever since. Hence “swine” flu. “Swine flu” has therefore always also been a “human flu.” In the human population, H1N1 viruses were replaced in 1957 by H2N2 viruses. However, in 1977 a H1N1 virus re-emerged. What scientists say today is that this virus most probably re-emerged because of a field trial with a new flu vaccine in China. So the virus was re-introducted due to a consequential accident. Ever since its “re-emergence,” H1N1 viruses have been circulating in humans.
The question now will be if the swine flu virus will be able to replace the current strains of the H1N1 virus which are already circulating. If not, the current doctrine will be even more out of joint than it already is.
The other vital question is how much protection current vaccines might provide if any.
Fifth, what is encouraging about the cases in New York is that they have all been mild. Keep in mind though, that the first wave of the pandemic of 1918 has been mild, too. The pathological is an emerging property.
Sixth, contrary to what the media and some experts are suggesting, pandemics do not necessarily kill more people than regular seasonal flu. The pandemics of 1957, 1968, and 1977 have been relatively mild. Of course, that doesn’t mean anything for the current event.
“The other vital question is how much protection current vaccines might provide if any”
on this point see the first blog entry ;
http://news.bbc.co.uk/2/hi/talking_point/8018428.stm
What do we know about the efficacy of current vaccines and/or cross-protection immunity from past vaccinations for H1N1 subtype influenza? On the one hand, I have read claims that the current virus is not preventable with vaccination. But I have heard other experts note that the prevalence of H1N1 subtypes in vaccines since 1976 should produce some immunity among those vaccinated in previous years. Thoughts?
I don’t think they will provide enough protection, but at this point the data is simply missing.
A few additions:
As soon as the media discovers the link between “swine flu” and the great pandemic of 1918, we will in all likelyhood see more of the “killer flu” language, whatever the actual numbers.
What has been most puzzling for experts so far are the stark differences between what we have been seeing in Mexico in comparison to the US, in terms of cases, mortality, and transmission.
As always with the flu, you never really know what is going to happen next. The virus might just as well suddenly disappear again. At this point, this scenario seems unlikely, of course, but you never know.
Thinking out loud… To answer Lyle’s question strictly as a matter of personal opinion: I believe current seasonal vaccines afford virtually no protection to H1N1, but a seed stock has been obtained for mass production of a vaccine should a decision to go forward be made. The adult age 20-40 cohort in the US probably has relatively little exposure to flu vaccine in all of its various subtypes owing to ACIP recommendations that it be administered to seniors and now more recently kids.
Another question, just based on the still-very-limited media accounts: the time between initial exposure and mortality. It seems that in Mexico, the spike in flu cases occurred in mid-March, but excess deaths did not appear until 2 – 3 weeks later.
… as expected:
Breaking News 1:48 PM ET: Swine Flu Prompts U.S. to Declare Public Health Emergency
legal authority granted under declaration of Public Health Emergency:
http://www.hhs.gov/disasters/discussion/planners/legalauthority.html#with
Not to put too fine a point on it, but I think at least one media report indicated that this event’s H1N1 reveals a novel genetic sequence. This precondition for declaration of a pandemic may therefore have very well been met.
The CDC media call ended just a bit ago and they provisionally answered Lyle’s question about cross-protection of already produced vaccines for the current virus. And it seems that Dale Rose was exactly right. They believe that there are no cross-reacting antibodies in the seasonal vaccine. But they still don’t know the reproduction number (or transmissibility (R0) rates) of the virus or its generation time.
Some studies claim that the R0 rate for the 1918 strain was just a little under two, which is not terribly high. But as Carlo mentioned they do vary, i just saw a second wave estimate of 3 and change.
So H1N1 doesn’t have to be hyper-transmittable to be globally deadly, but it would be nice to get some of these numbers even if they are likely to change.
… yes, a new genetic combination, but not a new subtype.
Edwin Kilbourne has just pointed out that it is important to know that he developed his concept of pandemics without subtype change on the basis of the 1947 vaccine failure and the occurence of extreme intrasubtypic change.
Carlo — I would be interested to hear a bit more from you about what the stakes are precisely in defining pandemic thresholds. Obviously it is a complicated scientific and institutional category — as important for what kinds of institutional response it summons into being as for the scientific specification of certain kinds of variation as particularly significant. Any thoughts on this?
“A new disease is, by definition, poorly understood†–WHO Director Margaret Chan, April 25 2009
It seems that a key aspect of transforming this outbreak into a “serious†event is the declaration that we are facing a “new diseaseâ€â€”and the fact that this novelty challenges our understanding. As Carlo pointed out, there are serious questions about what is new about the current strain. If not a new subtype, what about its novelty is significant? Tracking the production of this novelty—and the linking of novelty with risk—will be interesting.
The significance of its novelty in the context of *this* event is a) its genetic sequence/strain within a known subtype; b) the peculiar nature of its clinical manifestation (in terms of severity and mortality) which at the moment appears to vary along a geographic/national dimension, and c) simultaneous emergence across the globe. (A) and (C) would generally be expected in the context of a possible pandemic. The curious one for me is (b). I’m very curious how (b) will eventually be understood – i.e., what ‘explains’ differences in case mortality rates between the US and Mexico, for example.
What do you all think we should do from here?
Ummm…sorry to be picky here, but:
“Second, I have been reading now a couple of times that pandemics are affecting primarily young adults (not children and the elderly as during regular seasonal flu). However, this is true only for the pandemic of 1918, not the pandemics of 1957, 1968, and 1977.”
…is simply not true, for the 1977 pandemic. This affected young adults – under 25 – for the simple reason that H1N1 had vanished between 1957 and 1977 when it was replaced by H2N2, so this cohort had not been exposed to H1N1. See Encyclopedia of Infectious Diseases, http://tinyurl.com/r4bs, via Google Books.
Sounds like the Mexico Flu outbreak to me…?
Another sobering parallel between this and an earlier pandemic comes from the 1957 pandemic:
“The virus came to the U.S. quietly, with a series of small outbreaks over the summer of 1957. When U.S. children went back to school in the fall, they spread the disease in classrooms and brought it home to their families. Infection rates were highest among school children, young adults, and pregnant women in October 1957. Most influenza-and pneumonia-related deaths occurred between September 1957 and March 1958. The elderly had the highest rates of death.”
http://www.pandemicflu.gov/general/historicaloverview.html
SO this one is not yet over: the southern hemisphere flu season is just starting; the northern hemisphere season will resume in September – October. With a new, improved version of Influenza A H1N1 Mexico??