Southern hemisphere offers swine flu lessons

Updated Mon. Sep. 7 2009 10:01 PM ET

CTV.ca News Staff

Public health authorities now think they have a good idea of what to expect in this fall's expected "second wave" of swine flu - and most of it is good news.

As the southern hemisphere's winter season ends, an analysis of illness in Australia, Argentina, Chile, New Zealand, and Uruguay shows that while H1N1 dominated flu seasons there, it caused only a moderately severe pandemic.

"All countries report that after mid-July, disease activity in most parts of the country decreased," read a report published by the U.S. Department of Health and Human Services and other U.S. government agencies.

"This indicates that the duration of the current influenza season in the Southern Hemisphere, in which the 2009 H1N1 virus is the predominate strain, may be similar in length to an average seasonal influenza season."

The pandemic did stress health care systems in the south, but not for long, the report said. Health systems recovered - even without having the benefit of a vaccine to reduce infection rates.

All of that is good news, says infectious disease expert Dr. Andy Simor of Sunnybrook Health Sciences Centre in Toronto.

"It does spread easily, but it is not associated with higher rates of deaths, hospitalizations, or complications than with seasonal flu," he tells CTV. "So it doesn't appear to be more virulent or aggressive."

The southern hemisphere's experience has been similar to what countries in the north saw through the spring and summer's "first wave": high infection rates but generally mild disease, with only a small percentage of severe disease and death. In fact, little has changed since swine flu was first identified in Mexico last spring.

As well, there is evidence that the virus itself it not changing. Recent tests conducted on ferrets showed that H1N1 dominates other flu strains, and isn't attempting to mix with other strains.

"The H1N1 pandemic virus has a clear biological advantage over the two main seasonal flu strains and all the makings of a virus fully adapted to humans," said University of Maryland virologist Daniel Perez in a statement last week announcing his team's research.

The World Health Organization reiterated those findings last Friday, when it said that it too has not detected any mutation of the virus in its monitoring.

"It is not causing more severe illness than before, there have been no changes in the behaviour of the virus," WHO spokesman Gregory Hartl told a news briefing. "We are continuing to see increased number of deaths because we are seeing many, many more cases."

CDC Director Dr. Thomas Frieden told reporters that's good news.

"So far, everything that we've seen, both in this country and abroad, shows that the virus has not changed to become more deadly. That means that although it may affect lots of people, most people will not be severely ill," Frieden told reporters in a telephone briefing last week.

The Public Health Agency of Canada has studied more than 7,100 cases of swine flu in Canada including 1,400 patients who were hospitalized. Among them, there have been 72 deaths. Since many more cases of infection were likely not reported to health authorities, that suggests a death rate of less than one per cent.

While the death rate is low, the infection rate is high, but that's to be expected in the case of a novel virus to which most people have no immunity, says public health physician Dr. Richard Schabas.

In fact, the infection rate may be even higher than we know. Peru's Ministry of Health reported last month that its surveillance found that a third of swine flu cases presented more as the common cold, with no fever, while another third showed no symptoms at all, even though they were infected.

Despite the good news, there remain some worries for public health officials here in Canada as students return to schools and people huddle together indoors.

School-age children seem to be most at risk of serious illness, and are accounting for higher numbers of deaths compared to seasonal flu. Seniors over the age of 60 are generally thought to be less susceptible to infection because of exposure to previous H1N1 strains. But statistics from Australia and New Zealand suggest that among those who do become infected, there is a disturbingly high proportion of deaths.

Worries continue to remain for groups already identified at risk of serious complications from infection. They include pregnant women, those with obesity and/or chronic illness and people living in aboriginal communities.

The good news as the fall approaches says Schabas, is that this will be the second time many Canadians will be exposed to the virus, and many will have unknowingly developed some immunity with a previous infection.

"There certainly are a significant number of immune people in Canada, and that's going to reduce the impact of the second wave," he told CTV News in a phone interview.

"The worst we can expect to see is what was seen in Australia. There is no rational reason to expect it's going to be worse here than it was there. And there is good reason to believe it will be less severe."

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