Influenza is a seasonal disease. Some seasons are worse than others. In some locations they can be even more deadly than 1918 pandemic influenza (see post here). What characteristic, then, distinguishes a pandemic outbreak from "regular" seasonal influenza if it is not severity?
Severity is, on average, a characteristic of pandemic strain outbreaks because it involves a virus to which the general population has no or little previous immunity. There is another feature of pandemic outbreaks of importance: age distribution. Limited but fairly reliable evidence indicates that pandemic outbreaks have a shift of the age distribution to the "left," that is, toward younger age groups. Usual mortality from influenza is in the very young and the over 65 age groups but pandemic years add another group between them, the adolescents and young adults. This gave rise to the notorious W-shaped mortality curve of the 1918 catastrophe, with the hump in the middle being health young adults. We still don't know the reason for this distribution although a number of explanations have been advanced. The same shift, however, is seen in the milder pandemics of 1957 and 1968 so this doesn't seem like a feature confined to the 1918 strain but more something characterizing the infectious disease dynamics of pandemic strains in general. Whatever the reason, including in this case possible differential exposures, the shift in age distribution is also seen with the H5N1 cases:
The age group with the highest fatality rate was 10-to-19-years olds; 73 per cent of cases in that age range who contracted the virus died from it, noted the authors. (As is the practice of the Weekly Epidemiological Record, authors are not listed by name.)Sixty-two per cent of 20-to-29-year olds and 61 per cent of 30-to-39-year olds who tested positive for the virus succumbed to the infection, said the report.
By age 50 and older, the fatality rate dropped to 18 per cent, though the overall number of infections in older adults is low in comparison with younger age groups. In the very young -- under age five, and five to nine years of age -- the fatality rates were 43 per cent and 41 per cent respectively.
Adolescents and young adults weren't just more likely to die from the virus; they were also more likely to become infected in the first place, the review confirmed. The highest proportion of cases occurred in people aged 10 to 29 years.
In part, that might relate to the fact that many of the countries which have seen human cases have young populations, the authors said.
Exposure patterns in adolescents and young adults could also help explain the spike in infections in those aged 10 to 29, the report said, noting that young girls and women might be more at risk because they are often involved in culling, defeathering and preparing chickens for consumption. There were slightly more female cases than male, 106 to 97. (Canadian Press)
We know shockingly little about the 228 cases reported to date:
British influenza expert Dr. Angus Nicoll recently bemoaned the lack of detailed data on the human cases and disease outbreaks, calling it "a collective failure ... that must be overcome."Nicoll, who co-ordinates influenza activities at the European Centre for Disease Prevention and Control in Stockholm, complained that the number of analytical reports of outbreaks is "embarrassingly small."
"Consequently little more is known now than in 1997 about an infection that seemingly remains hard for humans to acquire, but is highly lethal when they do," he wrote in an editorial in the May issue of Eurosurveillance, an online publication on European communicable disease surveillance and control.
The above linked article in Canadian Press (no by-line, but I suspect it to be the excellent flu reporter Helen Branswell) takes note of a new report in WHO's Weekly Epidemiological Record, which also urges all countries to share clinical case data for the common good, including their own. I suspect this is aimed at China and Indonesia. The WHO report summarizes what we know about the first 205 laboratory confirmed human cases spanning the period December 1, 2--3 to April 30, 2006. This was a tabulation of surveillance data and hence its reliability for some of this information is unsure.
Still some general observations are possible. In the summer of 2005 the bird infection burst out of its Asian origins and spread geographically to Eurasia, Europe, the Middle East and Africa. The number of countries reporting human case increased from four to nine in that period. Changes in case fatality ratios are difficult to discern because of the uncertainty in the true number of infected cases (case fatality is the proportion of those infected that die from the disease). There are no compelling reasons to suppose it has changed substantially in the three year period covered by this report, however. It is still running in excess of 50%. Median interval from onset of symptoms to hospitalization is 4 - 5 days and median interval from onset to death is about 9 days. There is some missing data in this compilation but the broad picture seems unchanged during the time period. There does not seem to be an off-season, although there are more cases in the traditional northern hemisphere flu season of October to March of each year.
Considering the attention paid to the threat of a pandemic this is not as much information to go on as we might expect. Time for the countries involved to get serious about collecting and making available clinical information on their cases. This shouldn't be that hard to do. Clinicians have a built in interest to having this information to treat and manage their patients, so the problem is likely not at that level. It is at the level of the national health authorities in the countries where human cases are occurring. WHO was quite explicit:
Therefore, the sharing of data may be seen as part of an early warning system that will collectively defend all countries against a common threat. In May 2006, the World Health Assembly adopted resolution WHA59.211 calling for immediate voluntary compliance with provisions in the International Health Regulations (2005) relevant to the threat of an influenza pandemic. If countries comply with these provisions, they will greatly assist themselves, the international community and WHO in monitoring evolving situations and supporting adequate responses as well as enabling reliable risk assessments to be made (WHO).
Indeed.
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Revere You are correct, this same article is credited to Branswell on C-Health: Bird flu most deadly in teens and young adults. I haven't done a side by side check, but it appears to be the indentical article.
Hurrah for Branswell.
The Toronto Sun bylines their stories and this is Helen's work.
Thinking in terms of disaster response, my first thoughts do not drift to children. In a hurricane, one would think the people who stayed behind to were mostly adults. Perhaps protecting the homestead, or caring for grandma, too old and sick to move, mom and the kids bugged out for high ground two days ago.
That may be a naive, women and children first, way of thinking, but we protect our children from disasters, not rescue them from them. There is only one pediatric facility where I live and about seven adult facilities.
Hospitals have, (or should have), been working on pandemic planning for some time. Pediatric hospitals have been on the back burner so to speak. In the HHS series of checklists for institutional and community planning,
http://tinyurl.com/s7wkz ,(page12) children's hospitals are #11 of 15 and we're only at #9 now. Progress is, well, progressing. Having said that, assume capacity to care for them. We would use numbers of HCWs (RTs, RNs,etc),
hospital beds, (ICU, general), ventilators, etc. and apply them to an infection rate, (20-30% and a lot of opinions on variations of that). A great deal of our planning and preparation is number crunching, FluSurge 2.XXX and so on. What will we do in my community if 1/8 of our capacity is pediatric prepared, but 1/2 of the victims are children? I am currently working in an all grown up facility, where one sick and dying child would create a paralyzing nightmare. Perhaps there needs to be a parallel effort to have adult facilities bone up, (downsize?), their pedi capability.
WHO says so ( http://www.promedmail.org/pls/promed/f?p=2400:1001:1843854847753319695:… ):
"--- 2. Half of the cases occurred in people under the age of 20 years; 90 per cent of cases occurred in people under the age of 40 years;
3. The overall case fatality rate was 56 per cent. Case fatality was high in all age groups but was highest in persons aged 10 to 39 years; ---"
So if the rationale is that the older people, who have immunity against previous epidemics and pandemics are better equipped to meet the new one than the youngsters ("90 per cent of cases occurred in people under the age of 40 years"), why don't we vaccinate young people with as many flu vaccines as possible? If the older flus have indeed given even some immunity towards H5N1? Please explain... :)
Thinlina: When? Who? There isn't enough productive capacity or public health infrastructure to vaccinate the entire young population. Then there is the side effect issue if done in advance (see my earlier post on this issue). This isn't simple.
Yea, I know. A little provocative question, sorry. But if the young people would be vaccinated as soon as possible, we would have more time for vaccinations than if we start vaccinations only after the pandemic has blown full. If people were instructed to buy vaccines themselves if they only could, I believe quite many with any money would do it. Vaccination by itself isn't difficult, most people can learn it easily, if the technique was teached i.e. in TV.
How to produce vaccines? Most caountries have at least some capacity to produce them if only it was lawful.
http://penumbra-of-pandemia.blogspot.com/
Thinlina: The world's productive capacity is very limited and can't be increased easily. There aren't enough eggs, for one thing, not to mention the skills and physical plant. Using the productive capacity in this way would guarantee that it is the rich young people who would be vaccinated. But the side effect issue is important, as my previous post suggested. It is inevitable that serious events would occur if hundreds of millions are vaccinated (whether they are the result of the vaccine or just chance) and publicity about this in the absence of a pandemic might seriously hurt vaccination programs of all kinds. It is a complex problem. To say the least.
I know that the resources are scarce. But if we want to survive the next pandemic (in who knows how many waves...), we need to prepare by educating professionals in how to prepare vaccinations and we need to gather the means to make the vaccines.
I've seen a couple of patients with ADEM. It isn't nice to see. I just wonder, is it really just to deny public the information about the side effects of vaccination?
revere, please can you post the link to your earlier post about the vaccination side effects?
Thinlina: Here it is.
It is interesting to see the flu as compared by age groups but it would be interesting to see the death toll in regards to standards of living. Poverty is playing a big role here and it will take a lot more than vaccines to permanentaly tame this beast.
Wayne: You are spot on. This isn't just a biomedical problem. It is a social problem and a political problem. That's why public health has the word public in it.
revere, thanks.
You don't need to wait for a pandemic to vaccinate mismatch; immunity has prevailed even 40 years. Miamatch vaccinate today and when the pandemia comes (next autumn, next spring, the autumn after that...?), you'll have many immune people. Aren't we sure enough that the H5N1 will cause the next pandemic? Just give the sequence to vaccine producers, and they will boost economy and in the same time people will be immunized.
Psychological problems of side effects 1/1000000 cab be dealt with public information. Those who don't want to take the risk don't need to. Anyways, when the pandemia starts, there will be the vaccine against pandemic strain, and those who didn't want to take the mismatch risk can take the pandemic vaccine - if they want.
I think it's better to save peoples lives rather than psychologicak virginity - if you even need to choose between those two.
In many countries (to my knowledge at least in the Eastern Europe) there are a lot of physicists who drive a taxi ar waitress for living, because the doctor's work is so badly paid or there are not enough positions to get a doctor's work. Why not educate them for vaccine production experts? If there is shortage of expertice and human resources.
Thinlina: I agree with you that psychological damage is not the main worry. It can be dealt with. I was pointing to the damage to the vaccination programs from public suspicion. It could involve other vaccines as well. As I said in the post, what to do is not obvious (to me, anyway). A mismatched vaccine program might be the right thing or it might not. There are pros and cons here. It is not a no-brainer in my estimation.
So is there something else that you are not saying then? Are the side effects bigger than publicly admitted? If not talking about dead (one in a million, by the way do you reckon what is the death rate with NSAIDs?), what are the worst side effect when the patient remains alive? And what's the side effect frequency in those cases? Isn't mismatch vaccination happening every year, when the seasonal vaccination isn't effective enough for everybody?
After the first pandemic wave I really don't believe that the damage to the vaccination programs from public suspicion will be the biggest problem - probably the shortage of caskets will be more of a problem.
If you are referring to the swine flu vaccination program, I believe the public suspicion problems can, in a large part, be dealt with a good public information about the possible side effects. Anyways, people should be aware of the side effects always when they make the decicion about vaccination. Also they should be aware of the possible outcomes of not vaccinating. Taking risks informed consent is always better and more easily approved than when knowing the risks only afterwards.
I'd like to read answers, because I don't quite understand why we should take the risks of e.g. NSAID's but we must not take the risks of pre-pandemic vaccination.
Thinlina: I think it's a judgment call. People take NSAIDS voluntarily for symptoms. Vaccines are given to well people in the tens of millions. They may not be different numbers wise but people view them differently. I understand your point of view. I don't have anything to add.
hmm.