This time last year, doctors and public health leaders were anticipating one of the worst flu seasons in decades, as hundreds of thousands of children returned to school with no protection from a new influenza virus that was rapidly spreading around the world.
But it’s an entirely different story this year. Global health officials declared the swine flu pandemic officially over last week. And epidemiologists say the Bay Area and the rest of the United States probably will see a normal flu season this year – that means two or three strains will circulate, probably starting around midwinter.
The swine flu – a form of influenza Type A, subtype H1N1 – will almost certainly be one of those strains, but it won’t necessarily be the predominant strain and it isn’t expected to spread as widely as it did last year. That’s because so many people either were vaccinated and are protected or were infected by the virus last year and are now immune to it.
But influenza is a notoriously unpredictable virus, and what will actually happen this season is still a guessing game, flu experts say.
“H1N1 will probably behave more like our usual annual epidemic of flu. But how much stock you can put in anything around influenza, it’s hard to say,” said Dr. David Lewis, an infectious disease specialist with Stanford University School of Medicine.
That’s why doctors and public health officials are recommending that anyone who didn’t get the swine flu vaccine last year get the seasonal vaccine this year. This year’s seasonal vaccine will include protection from swine flu as well as one or two other influenza strains.
H1N1’s toll
The U.S. Centers for Disease Control and Prevention estimated that roughly 60 million Americans were infected with the swine flu between April 2009 – when the new strain was identified in the United States – and March 13 this year, when infection rates had fallen significantly. Roughly 12,000 deaths were attributed to swine flu in that time period.
That’s significantly fewer deaths than a normal year, which would see about 36,000 deaths from the flu. But the flu typically kills the elderly and people who have health problems that leave them vulnerable to illness.
The swine flu tended to attack younger people, especially those under age 40. The number of deaths of children from the flu in the United States was significantly greater – in a typical year, fewer than 100 children under age 18 die from influenza, but at least 276 children died from swine flu, according to the CDC.
Because the virus was new, and considered dangerous to so many, public health officials worldwide expanded vaccination efforts, and the United States developed one of the largest mass immunization campaigns in decades.
The drive to immunize large segments of the public may have helped reduce the number of infections and deaths, epidemiologists said last week. At the same time, the swine flu virus was not nearly as virulent and contagious as public health officials had feared.
Preparation worth it
But given the uncertainty that surrounds influenza – the strains of virus are capable of changing quickly as they spread from person to person – it made sense to prepare for the worst, said Art Reingold, head of epidemiology at UC Berkeley.
“There are people who believe there was an overreaction (to swine flu). I think they’re simply wrong,” Reingold said. “People can be smart in retrospect, but no one could have known a year and a half ago how this would turn out.”
Epidemiologists said the swine flu pandemic was a good dress rehearsal for future pandemics, involving deadlier influenza strains and a need for a quick, efficient public health response.
“It was wonderful practice for the pandemic that’s going to be more severe. And we have to believe something more severe is coming down the road,” said Dr. Larry Drew, head of the UCSF virology lab, which tests virus samples in San Francisco. “We needed the practice. We needed to have the alert raised.”
By Erin Allday