As we start the new year, about half the country is still susceptible to novel H1N1.
So far, about 50 million people have had the virus (31 million typically get the seasonal influenza each year). About 60 million have been vaccinated against H1N1, and roughly 50 million seniors are thought to have pre-existing immunity from long-ago exposure to a similar influenza virus.
Are the remaining 150 million Americans off the hook? H1N1 has already had two waves, one in late spring 2009 and one in early fall 2009. Will there be a third wave?
“To be honest, no one really knows,” Dr. Michael Osterholm told me — a humble disclaimer from a professional who understands as much as anyone about influenza and its behavior. I had asked the internationally recognized expert on infectious diseases and public health about a summary piece he wrote last month assessing the H1N1 public health situation.
What we do know is that in previous influenza pandemics, the virus came in several waves and the timing of those waves ignored the conventional seasonality of the flu, which is typically a dead-of-winter scourge. H1N1’s second run, starting in late August and peaking in mid-October, seemed at least chronologically related to the opening of the school season, but no one can be certain if this is cause and effect or just association.
Likewise, it makes sense that the traveling and population mixing that comes with our winter holiday break would set the country up for another surge of H1N1. We still have plenty of hot coals (the infected) and plenty more fuel (the susceptible), so why wouldn’t the stirring of the national pot over the holidays re-stoke the fire?
“The problem with that [metaphor] is that we’ve been stirring this campfire every day for the last 10 weeks, 12 weeks, 18 weeks,” Osterholm responded. “Going home for Christmas and coming back doesn’t really explain it to me. We’ve had ongoing transmission at the University of Minnesota campus right through the fall before we broke [for Thanksgiving], but it was just much less of it. And yet the number of susceptibles in all the classrooms and Coffman Memorial Union and Stub & Herb’s were all the same.”
“Measles wouldn’t do that. Measles would have just kept going through the population ’til it burned out of susceptibles. And none of us have a clue why that happens, and that’s why I am very cautious about predicting a third wave. There surely could be but we don’t know,” Osterholm cautioned. “Think about it: We had 46 states that had widespread transmission just nine weeks ago. Why did that die out? There are certainly enough people around to get infected.”
Break-out pandemic was anticipated but still surprising
Like the word “plague,” the term “pandemic” has a bit of an antique, yesteryear ring to it. But relatively recent outbreaks of the SARS and avian flu viruses have reminded us that despite our modern sophistication, a break-out virus causing a global pandemic was not only possible but even probable.
So the arrival of the novel H1N1 virus shouldn’t have been a surprise to anyone. And yet according to Osterholm, this wasn’t exactly what he and his colleagues were looking for.
The expectation was that a pandemic virus would be something new and different, not a subtly reworked version of an existing virus. After all, different strains of the H1N1 influenza virus had been hanging around for years as active purveyors of seasonal influenza.
“This virus is new from the perspective of lack of immunity [to it in the general public], but it isn’t new in the sense of the basic gene structure of the virus,” Osterholm told me. “A year ago everybody had heard of [standard] H1N1, and everybody would have agreed that’s the last thing that’s going to cause a pandemic because it’s already here. But this one was under our nose the whole time — it’s just different.”
So it came as a bit of a surprise that a virus so similar to existing H1N1 strains would be different enough to be altogether different — “the novel H1N1.”
A misunderstanding of the term ‘pandemic’
Yes, the term “pandemic” has a lethal ring to it, but it’s important to understand that pandemic criteria are defined by activity rates (how many people are infected simultaneously over a number of regions) and not by mortality rates. A pandemic virus by definition is highly infective but isn’t necessarily lethal.
A misunderstanding of what defines a pandemic has led many to ask the honest question: If this is a pandemic, how come more people aren’t dying? They look at the current mortality numbers for H1N1 (about 10,000 Americans) and compare those to what we’re told we see in a run-of-the-mill seasonal influenza outbreak (about 36,000) and then conclude that pulling the pandemic alarm was all a scare tactic.
Understanding how the Centers for Disease Control came up with an annual average of 36,000 deaths from seasonal influenza gives some clarity to the issue. In his mid-December update, Osterholm noted that “only 9,000 of those estimated annual seasonal deaths are due directly to influenza or secondary bacterial pneumonia. The other deaths are among persons who have influenza and who die of events like heart attacks or strokes.” Although that doesn’t seem to be a disingenuous way of calculating seasonal flu mortality, it certainly is generous.
“I don’t want to try and downplay the impact flu might have on a seasonal basis, but we have to be intellectually honest about it,” Osterholm responded. “That’s why I use the analogy of the guy who has a heart attack while using a snowblower and his death is attributed to the storm.” The snowstorm didn’t cause the man’s advanced heart disease, but it may have tipped him over. “You could argue that heart attack could have happened if he had been having sex that night. Would call you that sex-related mortality?”
So exactly how lethal has H1N1 been?
By Osterholm’s calculations, H1N1 is brandishing a lethality rate of 32 per million population. Compare that with the 1918 Spanish flu, which killed 5,000 to 7,500 per million population. Although these two pandemics have very different mortality rates, their victims have a very similar age range. Seventy-six percent of H1N1 deaths have come in people age 18 to 64; 11 percent in children up to age 17; and 13 percent in people over age 65. That’s an entirely different profile than for seasonal influenza, wherein more than 90 percent of deaths occur in the elderly. Even the influenza pandemics of 1957 and 1968 were like “seasonal flu on steroids,” noted Osterholm. “The vast majority of deaths were still among the elderly, but there was just a lot more of them.”
Comparing the ages of those who’ve died from H1N1 and those who’ve died from seasonal influenza, one realizes that comparing 10,000 to 36,000 isn’t exactly fair. This is why experts like Osterholm believe we need to move away from using raw mortality numbers to try to measure (and communicate to the public) pandemic severity.
“We have to get away from the descriptor mild, moderate and severe pandemics,” commented Osterholm. “Surely that works for individual cases, but it doesn’t work in this pandemic.” He suggests that thinking in terms of “Years of Potential Life Lost” is a truer measure of how a flu virus is affecting society. A 10-year-old lost to the flu had, on average, 70 more years to live. A 70-year-old had 10 more years to live. “If you use potential years of potential life lost, and we’re working on that right now, it’s dramatic what this virus did.”
Vaccine recalls: Not a safety issue
If you’re scanning headlines, you might have read about some H1N1 vaccine recalls and figured it was a safety issue. Why else would they pull a vaccine, right in the middle of a pandemic, after they’ve been clamoring for us to get it? Osterholm pegs it as a letter-of-the-law, regulatory kind of recall.
“It was never about safety. The vaccine never lost its potency. It’s just when they filled it [the vials], some of it got stuck, and it never got fully back into solution, and so you didn’t get the full hit. But it turns out that the hit that you got was more than enough to be fully protective.”
“Here’s a good example,” Osterholm offered. “I go out and buy a food product that says there are 32 fluid ounces in it. Well, it turns out the machine short-changed it and it was 31.9 fluid ounces, and those all get recalled.” Does the 0.1-ounce meaning anything to the consumer? Do they find themselves less satiated? “Every one of these recalls was sufficiently potent for you [the consumer], the problem was it just didn’t meet the label,” Osterholm stated. “We had no reason to believe that the vaccine you got wasn’t more than sufficiently antigenic to develop a high level of protective antibodies.”
And since one can’t talk about influenza vaccine without mentioning Guillain-Barré syndrome, let’s talk about Guillain-Barré syndrome, a serious but uncommon neurological disorder that most often follows an infection. When the nation was vaccinated against the swine flu virus of the mid-1970s, there was an increase in the number of cases of Guillain-Barré. H1N1’s partially-swine pedigree not only harmed the pork industry but raised concern about an increase in vaccination-associated Guillain-Barré cases. The CDC has been aggressively monitoring for Guillain-Barré, and according to Osterholm, case numbers have been flat or even slightly decreased (and as a general rule, the harder one looks for something, the more — not less — one finds). And the overall safety profile of the H1N1 vaccine has been excellent.
“One of the really, really good pieces of news about this [vaccine] is that there has been nothing associated with this vaccine from an adverse events standpoint that has been of any concern at all,” Osterholm noted. “And we have enough people vaccinated now in this country that even the very, very rare event would have been picked up by now.”
That’s good, because next week the Minnesota Department of Health, the Minnesota Coalition for Adult Immunization and other organizations are sponsoring the annual Ban the Bug vaccination campaign.
By getting vaccinated, you’ll also be helping to celebrate the Centers for Disease Control’s National Influenza Vaccination Week, and that’s a good feeling, isn’t it?