Swine Flu or Seasonal Flu?

A single influenza is circulating widely across the nation these days, and it’s the 2009 H1N1, aka swine flu. This included almost all of flu cases in the summer, and that trend has continued into the fall, according to the Centers for Disease Control and Prevention’s website.

However, in San Francisco, there is only one flu vaccine available right now, and it is for the regular, seasonal flu. The H1N1 flu vaccine is expected here at the end of the month and will be distributed through the same places where people get regular flu shots.

The CDC recommends that people get both shots.

Charles Chiu, a principal investigator at UC San Francisco whose lab studies emerging pathogens, including the 2009 H1N1 virus, said he understands that people might dislike getting shots, but he said it makes absolutely no sense to get the seasonal flu vaccine and not the swine flu vaccine.

Roughly 70 percent of seniors reported getting the flu shot in the last 12 months, according to a CDC study from early 2009. Over the same period, around 40 percent of adults under 65 got flu shots.

The vaccines, Chiu said, are made in precisely the same way and have the same level of risk. That risk is far outweighed by the danger of contracting the flu, he said. Also, healthy people can still transmit the disease to others, which is why the vaccine is recommended for health care workers.

Although regular, seasonal flu has been a negligible portion of flu cases through the summer, it may surface as we head into flu season, so health care officials are recommending people still get the seasonal flu shot.

The confusion over vaccines and the upcoming season has developed in part because health officials and scientists still know little about swine flu, which surfaced in April and continued through the summer, killing at minimum 4,100 people worldwide as of Sept. 27, according to the World Health Organization.

“What makes it dangerous is we don’t know,” Chiu said. “Overall it seems more benign than feared.”

“It’s actually quite different from other stuff out there,” Chiu said, calling it an “entirely novel strain.”

Because the virus is so uncommon, the CDC was particularly cautious about it when the world first became aware of the strain in April.

We now know the virus is a combination of several types of viruses, and six of its eight segments are from swine flu strains. However, it also has genetic material from human and bird influenzas too.

We also know that, compared with regular seasonal flu, this H1N1 strain poses less risk for older people and is more dangerous for children, the obese, those with respiratory problems and pregnant women. In the six weeks between Aug. 30 and Oct. 10, there were 43 influenza-related deaths in American children, 39 of which were confirmed to be H1N1, according to the CDC.

Only a small proportion of the hospitalizations have been people 65 and older.  One study of flu in Australia published in the New England Journal of Medicine showed that, over the three-month period studied during the Southern Hemisphere’s flu season, nearly 93 percent of hospitalizations were of patients under 65 years. Pregnant women in Australia were nine times as likely to be hospitalized compared to the rest of the population.

According to the California Health Department website, there have been 219 deaths from H1N1 and over 3,000 hospitalizations in California alone. As of Sept. 26, there were seven deaths and 65 hospitalizations from H1N1 within the county of San Francisco.

Though the swine flu has caused severe illness in a few people, most cases are relatively mild and Chiu guessed that overall, swine flu may prove to be less deadly than seasonal flu in terms of numbers. However, the deaths will occur in a different age group.

Researchers still have a lot of unanswered questions about the 2009 H1N1 virus:

Where on Earth did it originate? Though the virus was initially isolated in a Mexican town, Chiu said that it’s still unclear how far the virus had spread when it was first identified.

Since the CDC monitors the flu closely and regularly tests the seasonal virus, it seems unlikely that H1N1 would have been affecting humans for an extensive period of time before it was first identified in Mexico, but it is possible. Chiu’s lab conducted extensive studies of influenza in California over 2005 and 2006 and encountered nothing like this swine flu.

Did swine flu really start in pigs? “The cycle is pretty much birds, pigs and humans,” Chiu says. He is currently collaborating with Mexican researchers studying viruses in pigs in Mexico, and no one would be surprised if the flu emerged from pigs, but scientists have yet to confirm this.

When did the virus arise? Studies predict it began circulating around eight years ago.

What will happen as we enter the regular flu season? It’s unclear if people will start contracting seasonal flu as well, or if for some unknown reason the pandemic H1N1 flu will prevail. “It could be a limited niche,” Chiu said, but he added that it is really unknown and that is why the CDC recommends getting vaccinated against both kinds of flu.

There may not be as many of the usual seasonal flu cases this winter, but it is also possible that people could contract both. Little data exists on past pandemics to show if pandemic flu can overwhelm endemic seasonal flu.

Furthermore, though the regular flu occurs in flu season – which typically peaks around January or February but can range anywhere from late October through late April in the northern hemisphere – and scientists have several theories about why that is, no one actually knows why there is a “flu season.”

Some believe it’s because the winter weather preserves the virus better or allows for more rapid transmission. Another idea is people spend more time together indoors and therefore spread the virus quicker through close contact.

Will swine flu become endemic, reappearing every year in a new form? “No one really knows,” Chiu says.

How quickly will the swine flu mutate? Now that the virus has been in wide circulation for some time, the fears that it would rapidly change are being assuaged, but it is an unusual virus. Scientists are still investigating how quickly the flu can change or if it will combine with seasonal flu.

How many people have gotten swine flu? In April the world was counting known swine flu cases to the last digit. Today, no one knows precisely how many have caught it, and outpatients are not being tested. Scientists assume millions have or have had swine flu. The World Health Organization reports there have been more than 340,000 laboratory-confirmed cases.

No one has developed a test for antibodies to the swine flu – though it is feasible – so there’s no good way to measure the number of people who contracted flu and have since recovered.

Why do people avoid getting vaccinated? A recent survey by the Harvard School of Public Health showed that just 40 percent of people were sure they would get the H1N1 vaccine. The main reasons to avoid vaccinations were concern over vaccine safety or the belief that respondent has a low risk of contracting the flu.

Chiu stressed that the vaccine is as safe as the seasonal flu vaccine.