FluPortal.org

The CDC has just released new numbers on H1N1 — estimates of cases, hospitalizations, and deaths from April 2009 to mid-January 2010.

This CDC chart summarizes the data:

[CDC]

Click here to find the data broken down into helpful bar graphs. Also to learn how CDC compiles its estimates.

We blogged recently about a Pittsburgh-area study that suggests roughly 63 million Americans were infected with H1N1 in 2009. This estimate — although based on a methodology completely different from the CDC’s — falls in the mid-range of the CDC estimates. (Note: the CDC numbers include data for two extra weeks in January 2010.)

[Voces de la Frontera / cc (usable on your site) / Flickr]

A study (PDF file) released in February by the Institute for Women’s Policy Research suggests that the lack of paid sick days in the private sector increased the spread of H1N1.

Some of the study’s interesting findings:

• “The vast majority of public sector employees receive paid sick days, but two of five private sector employees have no access to paid sick days.”
• “[E]mployees who attended work while infected with H1N1 are estimated to have caused the infection of as many as 7 million co-workers.”
• “The data suggest that more than 90 percent of public sector employees, but only 66 percent of private sector employees, took time away from work when infected with H1N1 [...] implying that many more private sector employees felt that it was necessary to attend work while ill.”
• “[T]he drop in absence rates between October and November was twice as steep in the public sector as it was in the private sector, suggesting that contagion was less common in the public sector.”

The study goes on to propose that “similar patterns of absence” might be “found among children and students” depending on whether their parents “have access to paid sick days to care for family members.”

(Our usual disclaimer: we can’t vouch for the study’s methodology or results; we offer it up as something you might be interested in reporting on.)

[Update 4 March 2010: This is an issue that public-health experts have worried about throughout the H1N1 pandemic. New York Times article from November 2009 here and WNYC report from September 2009 here.]

[Disclaimer: We're featuring the following study and estimate as interesting food for thought. We can't vouch for their accuracy; you would need to do your own reporting to evaluate that.]

Two different assessments of U.S. immunity to H1N1 have emerged recently. The first suggests the number of Americans infected by swine flu in 2009 (roughly 63 million). The second estimates the number of Americans who currently have immunity to H1N1 (somewhere roughly between 150 and 165 million).

Ted Ross [U. of Pittsburgh]

Assessment #1: A new study published in PLoS Currents: Influenza estimates the number of Americans who were infected with H1N1 in 2009. (Read our post about PLoS — the Public Library of Science — here.) The lead author is Ted Ross, an associate professor of microbiology and molecular genetics at the University of Pittsburgh.

The study looks at levels of antibodies to 2009 H1N1 in Pittsburgh-area residents. (Infection with a virus stimulates antibody production, which then confers immunity.) It examines blood from “846 persons that ranged in age from 1 month to 90 years of age.” The samples were taken from “hospital and clinic patients in mid-November and early December 2009.”

It’s possible that some people with antibodies to 2009 H1N1 got them from the vaccine rather than infection with the virus — but “the timing of the sampling relative to vaccine availability in Pittsburgh suggests that these samples are likely from a largely unvaccinated population during the peak of the second pandemic wave.” In other words: the data probably approximate the number of people actually infected by H1N1 in 2009.

Here’s the study conclusion in a nutshell:

21% of persons in the Pittsburgh area had become infected and developed immunity. Extrapolating to the entire US population, we estimate that at least 63 million persons became infected in 2009. As was observed among clinical cases, this sero-epidemiological study revealed highest infection rates among school-age children.

Ian York [Michigan State University]

Assessment #2: Ian York, an assistant professor of microbiology and molecular genetics at Michigan State University, recently offered his best educated guess of the number of Americans now immune to H1N1 (on his blog Mystery Rays from Outer Space). As he puts it, there are three ways in which someone could have acquired immunity:

They could have been exposed to a related virus, some time in the past, and have developed a long-term immunity. They could have been infected with [H1N1], somewhere in the first or second wave. Or, of course, they could have been vaccinated.

He collects the available data for each of those categories — emphasizing that “[t]hey’re more or less approximate” — and concludes that:

• Over half the US population as a whole is now immune to the new [H1N1].
• As many as three-quarters of the elderly and two-thirds of the children — the most important populations as far as flu is concerned — may be immune.
• Between a third and about half of this immunity was due to vaccination.

To find York’s full table of high and low estimates — broken down by age group — click here.

Why is it useful to know what percentage of the population may have immunity to H1N1? As the PLoS study puts it, it “provides valuable information about the likelihood of a possible third wave and may be useful in decision-making about immunization strategies.” Or as York writes, the “level of immunity” that he calculated “is probably enough to impact virus transmission drastically.”

Vincent Racaniello
[Virology Blog]

The CDC’s new H1N1 data re-emphasize that, compared to seasonal flu, swine flu has disproportionately affected people under 65. Vincent Racaniello, a professor of microbiology at Columbia University, recently summarized a study done in mice that suggests one possible reason for this. The study appears to confirm initial hunches that many older people have immunity to swine flu because of previous H1N1 vaccines or bouts of flu.

The mice, Racaniello says, were inoculated with various past strains of H1N1 — and it turns out that several of those strains offered significant protection:

In other words, if you lived before 1943, or received the 1976 swine flu vaccine, you may be protected against infection with 2009 H1N1 virus. After the 1976 swine H1N1 outbreak at Fort Dix, NJ, approximately 40 million people in the United States were immunized with an NJ/76 vaccine. The NJ/76 swine virus never spread in the general population, but the vaccine against it has finally proven useful.

If you are less than 35 years old, you are more likely to be infected with the 2009 H1N1 virus because you did not receive the NJ/76 vaccine, nor were you infected with viruses that circulated from 1918-1943.

Racaniello blogs regularly at Virology Blog. You can find his previous posts exploring the same topic here, here, and here. The mouse study that Racaniello cites is here.

The CDC put out some new H1N1 numbers on Friday: on cases, hospitalizations, and deaths. The data span the period from April 2009 to 16 January 2010. The CDC emphasizes that its numbers are estimates based on a “nationwide surveillance system” and “statistical modeling.” It’s impossible to generate exact numbers for several reasons:

[M]any people with flu don’t seek medical care and only a small number of those that do seek care are tested. More people who are hospitalized or die of flu-related causes are tested and reported, but under-reporting of hospitalizations and deaths occurs as well.”

With those caveats, here are the estimated numbers:

CDC estimates that between 41 million and 84 million cases of 2009 H1N1 occurred between April 2009 and January 16, 2010. The mid-level in this range is about 57 million people infected with 2009 H1N1.

CDC estimates that between about 183,000 and 378,000 H1N1-related hospitalizations occurred between April 2009 and January 16, 2010. The mid-level in this range is about 257,000 2009 H1N1-related hospitalizations.

CDC estimates that between about 8,330 and 17,160 2009 H1N1-related deaths occurred between April 2009 and January 16, 2010. The mid-level in this range is about 11,690 2009 H1N1-related deaths.

To find a more detailed chart showing the numbers for three different age ranges (0-17 years, 18-64 years, 65 years and older), click here. This chart is especially interesting because it illustrates how strongly h1n1 has affected young people. The same page also explains the methodology CDC uses to generate its H1N1 data.

Last fall, we took a look at how news organizations were approaching the question what to call the new influenza pandemic — “swine flu” or “H1N1”? Nine months into the outbreak, it’s time to revisit this debate, and this time we’re taking it to the streets — the virtual streets of Google search terms. Using Google Insights for Search, we can see how “H1N1” and “swine flu” have been trending over the last year.

And by a clear margin, swine flu is the winner and champion. Last April, when the outbreak first appeared in Mexico and the United States, “swine flu” dominated the public consciousness, news reports, and our Google searches. The huge volume of these early searches gives “swine flu” a substantial victory in total number of searches over time.

But by the chart below, you can see that “H1N1” picked up the pace and essentially pulled even once the initial wave of “swine flu” searches died down. And in recent months, as the second wave of the pandemic lessened, “H1N1″ is occasionally the more popular search term.

There are also geographic differences in the popularity of the two search terms. Below are maps for “swine flu” in red and “H1N1″ in blue. The darker the color, the more common the search. Between April 09 and January 2010, West Virgina, Utah and Maine produced the most searches for “swine flu”. During the same period, the upper Midwest led the way with the most “H1N1” searches.

Another interesting set of data to look at is the differences in related search terms. “Swine flu” searches have been more often associated to finding information about the symptoms. “H1N1″ searches, on the other hand, are more likely to be about vaccine information.

This kind of search data can provide an interesting window into both the rhetorical trends of media and how we talk about the pandemic. Perhaps we tend to use “H1N1” in more medical and scientific contexts –- the research, the pandemic data, and the vaccine. In contrast, “swine flu” may have been the choice in describing the illness, its traits, and the experiences of those who caught the flu.

You can do your own search term analysis at Google Insights for Search.

In yesterday’s CDC press briefing, Ann Schuchat, Director of CDC’s National Center for Immunizations and Respiratory Diseases, gave a post-holiday roundup of the latest H1N1 developments.

Here’s the short course: The vaccine is now available to pretty much everyone who wants it all across the country. So far, the US hasn’t decided to return/donate/sell any of its vaccine supply as some European countries are doing. Instead, it’s focusing on the upcoming (10-16 January) National Influenza Vaccine Week (NIVW). NIVW is another big push to encourage Americans to get H1N1 and seasonal-flu shots. It has its own schedule of activities, informational materials, a media toolkit, and web tools like ecards and badges.

Why continue pushing the H1N1 vaccine when, as Schuchat announced, “we’re seeing drops in laboratory confirmed hospitalizations and deaths”? Because there’s also “activity increasing in a few other indicators.” She clarified:

We still have more activity than we usually have this time of year, though it’s certainly much below where it was several weeks ago. All the virus that we’re seeing right now is the H1N1 virus. We haven’t yet seen the emergence of seasonal flu strains in any numbers at all. We saw a slight uptick in the last week’s reporting in the influenza-like illness visits to the doctors or emergency departments. That can sometimes happen right around Christmas, so we don’t know if that will persist. We also saw an uptick in pneumonia or influenza deaths in this past week. And that isn’t something that we necessarily see around the Christmas holiday.

Minnesota was one state that reported increased influenza-like illness last week.

What CDC is afraid of, of course, is a third wave of H1N1. To drive the point home, Schuchat showed this graph of pandemic mortality in 1957:

[CDC / usable on your site]

She went on to say:

This is really a reminder of why we are saying that we need to remain vigilant. [...] [I]f you look at this graph, the bottom part of that curve, you know, the — there’s the camel hump and then it comes down to that valley. Well, that’s where we are right now in that valley. We don’t know what’s going to happen over the next several weeks or months. But in 1957, this essentially gave the all clear whistle in that December/January time period. They had vaccine, but they didn’t encourage its use and yet they did go on to see that increase in mortality.

National Influenza Vaccine Week launches on Sunday. You can check here for NIVW activities in your area.

[courosa / cc (usable on your site) / Flickr]

Two polls released just before the holidays give some new figures on H1N1 vaccination rates in the US: one by the Harvard School of Public Health (HSPH) and one by the National H1N1 Flu Survey (NHFS). The HSPH poll was conducted on 16-17 December, 2009. The NHFS poll was conducted on 6-12 December, 2009.

The HSPH results include the following:

The NHFS results include these numbers:

[Ian-S / cc (usable on your site) / Flickr]

The World Health Organization released a briefing note last week on death rates from H1N1 and from seasonal flu. It warned that comparisons are “not reliable for several reasons and can be misleading.”

The note explains that seasonal-flu death rates are based on models that create estimates; whereas H1N1 death rates are currently based on lab-confirmed deaths, which are “unquestionably” lower than the actual totals. WHO says that it won’t be until “one to two years after the [H1N1] pandemic has peaked” that “accurate assessments of mortality and mortality rates will likely be possible.”

The briefing note also points out that comparing death rates misses an important point: H1N1 appears to be more lethal for younger people than typical seasonal flu.

[Orin Zebest / cc (usable on your site) / Flickr]

Several new scientific studies of H1N1 have been released in the last few days. We’re highlighting four that might interest you because they appear to answer some common questions about swine flu. (Disclaimer: we’re not in a position to evaluate the quality of the research.)

Question: Is it OK to eat pork from a pig infected with H1N1?
The Department of Agriculture has consistently maintained that you can’t catch H1N1 by eating pork. Now they’ve followed that up with a study showing that pigs infected with H1N1 are safe to eat. (A PDF of the press release is here.) The virus appears not to be present in tissues other than those from the respiratory tract. The researchers found “no evidence for systemic infection that would contaminate meat with infectious virus.”

Question: How is H1N1 sometimes fatal?
Brazilian researchers, examining 21 fatal cases of H1N1, have concluded that the cause of death was typically due to lung damage (of various kinds). In other words, despite the variety of systemic symptoms caused by H1N1, “the main pathological changes associated with [H1N1] infection are localized to the lungs.” Apparently one quarter of the patients did not have any underlying complicating medical condition. (The full study will be published next month in the American Journal of Respiratory and Critical Care Medicine.)

Question: Is H1N1 more dangerous for children than seasonal flu?
A retrospective study of children who died of H1N1 this spring/summer in Buenos Aires says: yes. It concludes that the “rate of death [from H1N1] was 10 times the rate associated with seasonal influenza for the same population in 2007 and 5 times the rate reported by the CDC for the U.S. pediatric population during the relatively severe 2003–2004 influenza season.” The mortality rate for infants was especially high (“10 times the U.S. infant death rate from seasonal influenza in 2003–2004″).

Question: Do pregnant women really have an increased risk of dying from H1N1?
A retrospective California study of “reproductive-age women” (pregnant or not) who were “hospitalized with or died from 2009 H1N1 influenza” suggests this is true. It also concludes that, for pregnant women, antiviral treatment within 2 days of symptom onset reduced risk of admission to an ICU and/or death. About one third of the pregnant patients in the study had other “risk factors for complications from influenza.”