I wonder if that might not be because older people have generally been urged to get flu shots and many have for years. Could it be that there might be some residual immunity from all those shots, and that those shots may have contained enough similar sections of the virus to impart partial immunity?
This article touches on the 1918 immunity
More evidence that the new H1N1 virus is more dangerous than seasonal flu: The new Kawaoka paper
A paper has just come out from Dr. Yoshihiro Kawaoka’s group describing their findings regarding the respective dangers of the new, pandemic H1N1 and seasonal flu (see reference below). Although this work supports two recent studies with ferrets suggesting that the new H1N1 causes more illness than seasonal flu, the new study provides additional insights into the pathology caused by H1N1.
Mice, ferrets, monkeys and pigs were given either the new H1N1 or a seasonal H1N1 intranasally. The following new H1N1 strains were used:
* A/California/04/09
* A/Wisconsin/WSLH049/09
* A/Wisconsin/WSLH34939/09
* A/Netherlands/603/09
* A/Osaka/164/09
These strains were all isolated from individuals with mild disease except A/Wisconsin/WSLH34939/09 which came from a person who had been hospitalised.
In mice, ferrets and monkeys the new H1N1 strains caused more severe disease than the seasonal H1N1 strain. However, in pigs, few clinical signs were observed with the new H1N1 suggesting that the virus may be spread asymptomatically in this species.
The amount of virus necessary to kill 50% of the mice was examined with the different strains. Less virus was required to kill mice with most of the new H1N1 strains than with the seasonal H1N1 . A/Wisconsin/WSLH049/09 was equally lethal to the mice as seasonal H1N1. Of the new H1N1 strains, A/Wisconsin/WSLH34939/09 was the most lethal. This is the strain isolated from an individual that had been hospitalised.
Striking differences in lung pathology in mice, monkeys and ferrets were observed between animals that received the new H1N1 virus as compared to animals that received seasonal H1N1. In particular, the lungs of monkeys that received the new H1N1 exhibited similar pathological changes to those seen in animals exposed to H5N1.
Transmission between ferrets by aerosol droplets was similar in animals infected with seasonal or pandemic H1N1.
One notable, and surprising, finding of this study was that neutralising activity was found in sera collected from the residents of nursing home that were born before 1920, but none in those born after. Thus, only those exposed to the 1918 virus are likely to have antibodies that recognise the new H1N1. Therefore, the relative paucity of deaths among people in the 60 to 89 age range cannot be explained by exposure to a virus that conferred cross-protection to the new H1N1.
In comparing this study with the two previous studies using ferrets, I am again struck by the parallels between the severity of disease observed in its human host and the ability of particular isolates to cause disease in animals. A/Wisconsin/WSLH34939/09, which was the only strain isolated from an individual who had been hospitalised, was the most lethal in mice. This adds further support for my hypothesis that the new H1N1 is unstable and causing variable disease due to variations in the virus itself.
Future studies explicitly comparing pathology in animals caused by virus isolated from patients with different clinical outcomes may be informative. If this association holds up, sequence analysis may provide clues into which variants of the virus are most likely to cause severe disease.
Reference:
Itoh, et al. (2009) In vitro and in vivo characterization of new swine-origin H1N1 influenza viruses. Nature, doi:10.1038/nature08260
swine flu
Karaoka and his team looked at nursing home residents and workers from 1999 and from workers and patients in a hospital from this year (2009). Almost all the sera with neutralizing antibodies came from people born before 1920, a fact they interpreted as meaning that the current swine flu is related to the original 1918 virus before it diverged
The Associated Press
Posted: 07/14/2009 10:56:23 AM PDT
VALLEJO, Calif.—Nurses at a northern California hospital say inadequate masks and air-filters have resulted in medical staffers becoming ill while caring for three swine flu patients. ...
http://www.mercurynews.com/breakingnews/ci_12834125
Flu expert: ‘More will die’ if strike drags on
http://mobile.thestar.com/mobile/NEWS/article/668321
July 18, 2009 04:07:00
Theresa Boyle
HEALTH REPORTER
Toronto will see more deaths from the global H1N1 pandemic because of the civic workers’ strike, warns the head of infection control at Mount Sinai Hospital.
“The bottom line is more people will die,” microbiologist Dr. Allison McGeer, a respected authority on pandemic planning who has consulted for all three levels of government on the issue, said yesterday.
On the picket line are as many as 1,800 unionized employees from the Toronto Public Health Unit, which is supposed to be playing a critical role in the battle against the H1N1 influenza virus, particularly in planning for the second wave, which is feared to hit North America in September with a vengeance.
“We are already in trouble. Now we’ve got 26 days of work that hasn’t been done,” McGeer said.
Instead of being on the picket line, public health nurses, doctors, epidemiologists and other health unit staff should be providing pandemic management advice to school boards, long-term care facilities, jails, the Toronto Police Service, Toronto Fire Services and other essential services, she said.
They should be tracking the spread and severity of the virus, following up on cases where people have tested positive, and making plans for the establishment of vaccination clinics and flu assessment centres.
They should be organizing ways to help the homeless, shelter residents and people who don’t have family doctors. And they should be ensuring that plans are in place to quickly communicate updated pandemic response instructions to the general public and to health-care providers.
“We are expecting them to have spent the summer doing this. ... They are the experts in pandemic planning,” McGeer said.
“None of those things are getting done and the longer the strike goes on, the less likely they are going to get done,” she warned.
But Toronto’s medical officer of health, Dr. David McKeown, insists the strike has had no bearing on the city’s response.
“Planning for a pandemic in the context of the current H1N1 outbreak is something we identified as a critical service to be maintained during the strike, so non-union staff have been continuing with our planning efforts,” McKeown said last night.
Asked if the same level of service is currently being provided as would have been provided were there no strike, he responded: “I think we’re doing what we need to be doing at this point.”
McGeer said managers are doing their best, but it’s impossible to fill the vacuum.
As for front-line workers, she said: “I’m sure that the people who are out on strike are really unhappy about recognizing that they can’t be doing what they know needs to be done.”
Privately, senior officials at the city who are not on strike have agreed with McGeer’s assessment, expressing concern about the fall when a second wave of H1N1 is expected to hit. Managers are getting burned out, they say.
The health unit is now staffed by about 200 non-union employees and managers. They are also contending with health issues arising from piling-up garbage.
Sources say restaurant inspections are being done only on a complaint basis.
Ontario’s pandemic plan calls for the province’s 36 public health units to play a central role in containing spread of the virus and minimizing illness.
With Toronto’s health unit hobbled by the strike, not only will the city see more deaths, but there will also be more infections and hospitalizations, McGeer said.
“The whole goal of the (pandemic) plan is that fewer people die. It’s very simple,” she said.
Public health should be declared an essential service, like police and fire, so that employees are not able to strike, McGeer argued.
“I really struggle with our Toronto Public Health not being an essential service,” she said.
Her comments come days after the World Health Organization warned that the virus is spreading faster than any other pandemic in history, that production of a vaccine has been delayed and that one may not be ready until the end of the year.
Of all the province’s public health units, Toronto’s has by far seen the most H1N1 activity. Latest numbers show that there have been six related deaths and 85 hospitalizations.
What the second wave of the pandemic will bring is still a big question mark. At the very least, it’s expected to surpass the impact of regular seasonal flu, which has a role in 50 to 70 deaths in Toronto annually.
But there is a fear it could mimic the 1918 Spanish flu, which infected one-third of the world and contributed to the deaths of more than 50 million.
McGeer said the public health unit was already behind the eight ball before the strike.
Public health, in general, is woefully underfunded and under-resourced, she said, noting that the H1N1 outbreak was a challenge to deal with even with the full complement of staff.
“In terms of pandemic planning, it’s causing a terrible problem because we know that the amount of pandemic planning that the Toronto Public Health Department can do when it’s on strike is very, very limited,” McGeer said.
She pointed out that five royal commissions in the past 12 years have warned that public health is substantially underfunded.
“When I have been part of stakeholder groups and focus groups about what our goals should be for a pandemic and what we are aiming to do in Canada ... Canadians tend to talk about being sure that we have protected the most vulnerable people.
“That we can have that sense as a society and not fund pubic health is a complete mystery to me,” she said.