What is the status of the Pandemic???

If you are confused about the "state of the novel H1N1 pandemic," don't feel alone. The past few weeks have seen a variety of media reports, scientific publications, and blog posts that support, or at least imply, the conclusion that the current influenza pandemic is likely the "mildest on record" and seems to be waning. You might also have seen stories asserting that such public health agencies as the World Health Organization (WHO and the US Centers for Disease Control and Prevention (CDC) have had evidence that this was a mild pandemic months ago and yet have continued to hype its seriousness.


But if you look at written reports and statements from these same international and federal health agencies, you'll find they have made the case that this pandemic has extracted a severe price, particularly among children and younger adults, is far from over, and that it's critical to get as many people as possible vaccinated as soon as possible.

Trying to predict the next steps of a virus like H1N1 is always risky.

Three critical questions should be front and center for you, your family, and your organization:

1. Has this pandemic to date been a big deal or has this been a bunch of hype? Or maybe it's been somewhere in between?

2. Where are we in this pandemic experience? Is it over—or is another big "shoe" about to drop?

3. If it's not over, what should you be doing for yourself and your family to be better prepared, and what should your organization be doing?

Big deal or a bunch of hype?

Without a doubt, this pandemic has been a big deal worldwide if you, a loved one, or a member of your organization has been seriously ill, even worse if you've lost someone to the disease or its complications. Just last Thursday the CDC updated its estimated number of H1N1-related US cases and deaths. As of November 14:

Deaths. Approximately 9,820 people have died (estimated range, 7,070 to 13,930)

Infections. More than 47 million people have been infected (range, 34 million to 67 million)

Hospitalizations. Some 213,000 persons have been hospitalized (range, 154,000 to 303,000)

Of course, there is one number that we often hear, especially when people try to compare the impact of the H1N1 pandemic to seasonal influenza. It's usually cited this way: "Approximately 36,000 people in the US die each year from seasonal flu." Its source is a single 2003 CDC modeling paper. In short, this seems like a no-brainer: 9,820 people have died from H1N1 to date and we expect 36,000 to die annually from seasonal influenza. Let's provide some perspective behind the 36,000 figure:

1. Comparing apples to oranges. In that CDC study, 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.

2. The elderly. More than 90% of the estimated seasonal influenza deaths occur in the elderly, who in many instances have existing serious health conditions that mean their deaths may not be far off, regardless of their influenza illness.

How can we measure the pandemic impact today?

Let's take a closer look at the numbers of deaths associated with the H1N1 pandemic. Of the estimated 9,820 deaths:

1,090 (11%) have occurred in children 0-17 years of age

7,450 (76%) in people 18-64 years of age

1,280 (13%) in people over 65 years of age

This age distribution differs considerably from what we see with seasonal influenza.

Another comparison that is very important is how the current H1N1 pandemic compares to past pandemics. If we look at the rate of deaths in the US population from novel H1N1 through November 14, the 9,820 deaths among the US population of 308 million translates to a figure of 0.003% (or 32 deaths per million population).

The rate of deaths per age-group varies this way:

14.9 deaths per million children 0 to 17 years of age

38.9 deaths per million adults 18 to 64 years of age

33.0 deaths per million adults 65 years of age and older.

If we look at deaths for the dreaded 1918 pandemic, the estimates range from 500,000 to 750,000 deaths among a population of 100 million (0.5 to 0.75% or 5,000 to 7,500 per million). While there remains some ambiguity in the 1918 death numbers and how they were determined, they are at least 150 times higher than what we've seen to date with the H1N1 pandemic. Like the current pandemic, the 1918 deaths occurred at a much higher rate in young adults.

Similarly, when we look at the 1957-58 and 1968-69 pandemics, death rates are substantially higher than we have documented to date with novel H1N1:

In the 1957-58 pandemic, an estimated 70,000 deaths occurred among 172 million US residents (407 per million).

In the1968-69 pandemic, an estimated 34,000 deaths occurred among 200 million US residents (170 per million).

Like seasonal influenza, many of the deaths in both of these two pandemics occurred in the elderly population. In other words, they were more like "super-seasonal influenza" years.

Two other pieces of important data were notable in the CDC's H1N1 update last week. To date, the pandemic has caused:

1. More cases than seasonal influenza. To date, we know of an estimated 47 million cases of novel H1N1. That's already 16 million more than the estimated 31 million cases that occur during an average seasonal influenza year.

2. More hospitalizations than seasonal influenza. An estimated 213,000 hospitalizations to date have been related to H1N1 illness. That number exceeds by 13,000 the estimated average seasonal influenza year of 200,000 hospitalizations.

We're still a long way from being done with this pandemic; a third wave during the traditional winter flu months is still a possibility.

So yes, this current pandemic is causing fewer deaths than the three previous ones, particularly compared with 1918. Still, this pandemic is causing a marked increase in deaths in younger adults and children compared with a typical seasonal influenza year. It's challenging our healthcare system unlike any previous seasonal influenza season over the past 30 years.

Where are we in this pandemic experience?

So, does the rapidly waning second wave, which began in North America in mid-August, mean the end of the pandemic?

Infections. The estimated 47 million cases of H1N1 infection to date means that only 15% (47 million/308 million) of US residents have immune protection from an H1N1 infection.

Vaccinations. Last week, the CDC reported about 73 million doses of vaccine have been shipped to the states. If even 75 million Americans get vaccinated, that represents only 25% of the population.

Existing immunity. Given that there appears to be some residual acquired immunity in people over 65 years of age and who were exposed to a "cousin" of the current H1N1 virus before the 1950s, we can add on a guesstimate of another 10% to 15% of that population who have existing immunity.

When you add up the percentages of the three ways people can be protected against this novel H1N1 virus, we find that almost half of all residents in the US are still susceptible to infection and will be come this January. In countries where there is no or limited vaccine access, the percentage of citizens not yet protected will be even higher.

Given these numbers, is there any good reason why we won't have a serious third wave of disease in the Northern Hemisphere during this upcoming traditional winter influenza season.

What should you do now?

The first and most important step to remember is this: vaccine, vaccine, and vaccine.

As for your organization, go back over what you learned about the impact that the fall wave had on your operations. Given what you learned, ask what can you reasonably do to be better prepared for a similar, if not more significant, winter wave? Know that if that wave doesn't materialize, you wasted little. This H1N1 virus may be the predominant seasonal flu strain for years to come, so you'll not waste your time or a vaccine dose if you get it now. And of course the preparedness work you do now to collect and respond to lessons learned during the fall wave will be used some day in the future, even if only for the next pandemic.

This current H1N1 pandemic is surely not of a magnitude of the 1918 pandemic, or even the 1957 or 1969 pandemics. But it is a serious public health threat, and it's far from over. Expect the unexpected! That's the flu business.

—Michael T. Osterholm, PhD, MPH, is Director of the Center for Infectious Disease Research & Policy (CIDRAP), Director of the NIH-supported Center of Excellence for Influenza Research and Surveillance within CIDRAP, Editor-in-Chief of the CIDRAP Business Source, Professor in the School of Public Health, and Adjunct Professor in the Medical School, University of Minnesota.