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 already achieving what we would hope to achieve 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, says Dr. David Fisman, a University of Toronto expert in infectious disease dynamics.
Fisman can't understand the rational 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.
"I'm sure that the vaccine has prevented some deaths. I'm sure that there are people who are alive right now who would not have been alive if we hadn't vaccinated," he says. But 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," says Fisman, an associate professor of infectious diseases epidemiology at the University of Toronto's Dalla Lana School of Public Health.
Someone vaccinated today may be protected against infection two weeks from now, "if there is still enough of (H1N1) kicking around," Fisman says. But the benefit diminishes the further into the future we go, and he says 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 usual activities were cancelled or postponed as public health was forced to bear the brunt of delivering the largest immunization program 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 says.
-- Canwest News Service