Ronan Kelly
Retired 2020
Expert questions continuing H1N1 vaccinations
Health officials still urging people to get the shot
By Sharon Kirkey, Canwest News ServiceDecember 5, 2009 7:54
With H1N1 poised to enter history as the least deadly of four global flu pandemics, some experts are calling for an end to Canada's mass vaccination program.
Nature is achieving what we would hope by vaccinating, they say.
H1N1's "reproductive number"-- the number of people each infected person passes the virus to -- was above one when the epidemic began, which led to the explosive initial increase in cases.
Now it is less than one, because many people have become immune, and each old case is making less than one new case. When the reproductive number falls below one, the epidemic can't sustain itself and fades away.
The drop in cases suggests Canada has hit the critical fraction of the population that needs to be vaccinated to control the pandemic, said Dr. David Fisman, a University of Toronto expert in infectious disease dynamics.
Fisman can't understand the rationale for continuing mass vaccinations. He said that for a virus as contagious as H1N1, fewer than 30 per cent of the population needed vaccination to reach a critical level of immunity.
He noted that the pandemic was already peaking, and then subsiding before the vaccination was rolling out in force. "That's nobody's fault, that's just how long it took to make a vaccine against a brand new virus. Those were the cards we were dealt."
Despite that view, Canada's top doctor this week pleaded with Canadians to get vaccinated if they have not done so.
Chief public health officer David Butler-Jones said while 30 per cent of the population is now immune to H1N1, either because they have been vaccinated or because they have been infected, "millions" of people are still at risk of infection.
Someone vaccinated today may be protected against infection two weeks from now, "if there is still enough of (H1N1) kicking around," Fisman countered.
But the benefit diminishes the farther into the future we go, and he said other public health programs have suffered as staff and resources were redeployed to the H1N1 campaign.
In some jurisdictions, breastfeeding support programs, sexually transmitted diseases clinics and other activities were cancelled or postponed as public health was forced to bear the brunt of delivering the largest immunization in Canada's history.
"At this point, in terms of saying everybody must get vaccinated because there is a pandemic abroad, it's kind of done," Fisman said.
H1N1 will likely die out with a death rate lower than that for regular seasonal flu.
Harvard University infectious disease expert Marc Lipsitch is pegging H1N1's case fatality rate--the proportion of people infected with a disease who die of it--at less than 0.1 per cent, placing human swine flu in a Category 1 pandemic, the lowest level of severity for a worldwide disease outbreak.
Swine flu's case fatality rate is less than what was seen for the three worldwide flu outbreaks in the 20th century: 1918, 1957 and 1968.
Unless the virus mutates, and there is no strong sign H1N1 is becoming noticeably different, "it's almost certainly going to be the mildest of the four (pandemics) that we have good data on," said Lipsitch, a professor of epidemiology at the Harvard School of Public Health.
Lipsitch said that when the first reports were coming out of Mexico, the case fatality rate estimates were as high as four per cent, which is twice the rate for the 1918 Spanish flu.
http://www.calgaryherald.com/health/Expert+questions+continuing+H1N1+vaccinations/2307218/story.html
Health officials still urging people to get the shot
By Sharon Kirkey, Canwest News ServiceDecember 5, 2009 7:54
With H1N1 poised to enter history as the least deadly of four global flu pandemics, some experts are calling for an end to Canada's mass vaccination program.
Nature is achieving what we would hope by vaccinating, they say.
H1N1's "reproductive number"-- the number of people each infected person passes the virus to -- was above one when the epidemic began, which led to the explosive initial increase in cases.
Now it is less than one, because many people have become immune, and each old case is making less than one new case. When the reproductive number falls below one, the epidemic can't sustain itself and fades away.
The drop in cases suggests Canada has hit the critical fraction of the population that needs to be vaccinated to control the pandemic, said Dr. David Fisman, a University of Toronto expert in infectious disease dynamics.
Fisman can't understand the rationale for continuing mass vaccinations. He said that for a virus as contagious as H1N1, fewer than 30 per cent of the population needed vaccination to reach a critical level of immunity.
He noted that the pandemic was already peaking, and then subsiding before the vaccination was rolling out in force. "That's nobody's fault, that's just how long it took to make a vaccine against a brand new virus. Those were the cards we were dealt."
Despite that view, Canada's top doctor this week pleaded with Canadians to get vaccinated if they have not done so.
Chief public health officer David Butler-Jones said while 30 per cent of the population is now immune to H1N1, either because they have been vaccinated or because they have been infected, "millions" of people are still at risk of infection.
Someone vaccinated today may be protected against infection two weeks from now, "if there is still enough of (H1N1) kicking around," Fisman countered.
But the benefit diminishes the farther into the future we go, and he said other public health programs have suffered as staff and resources were redeployed to the H1N1 campaign.
In some jurisdictions, breastfeeding support programs, sexually transmitted diseases clinics and other activities were cancelled or postponed as public health was forced to bear the brunt of delivering the largest immunization in Canada's history.
"At this point, in terms of saying everybody must get vaccinated because there is a pandemic abroad, it's kind of done," Fisman said.
H1N1 will likely die out with a death rate lower than that for regular seasonal flu.
Harvard University infectious disease expert Marc Lipsitch is pegging H1N1's case fatality rate--the proportion of people infected with a disease who die of it--at less than 0.1 per cent, placing human swine flu in a Category 1 pandemic, the lowest level of severity for a worldwide disease outbreak.
Swine flu's case fatality rate is less than what was seen for the three worldwide flu outbreaks in the 20th century: 1918, 1957 and 1968.
Unless the virus mutates, and there is no strong sign H1N1 is becoming noticeably different, "it's almost certainly going to be the mildest of the four (pandemics) that we have good data on," said Lipsitch, a professor of epidemiology at the Harvard School of Public Health.
Lipsitch said that when the first reports were coming out of Mexico, the case fatality rate estimates were as high as four per cent, which is twice the rate for the 1918 Spanish flu.
http://www.calgaryherald.com/health/Expert+questions+continuing+H1N1+vaccinations/2307218/story.html