Mild Winter May Be Keeping Flu Bugs At Bay

Flu season usually peaks around February. But this year it's missing in action, with the CDC reporting the slowest start to the flu season on record. Peter Palese, a microbiologist at Mount Sinai Medical Center, discusses whether unseasonably warm winter weather may be to thank.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. It's been a wacky winter, hasn't it been? At least here in the East, we're enjoying springtime weather, the birds are chirping, buds coming out. The pollen count in Chattanooga, Tennessee, this week was over 1,300, mostly tree pollen. That's in the dead of February.

And where's all the snow? And where is the flu season? Right, remember the other winter tradition? The flu season is supposed to be peaking right now. The Centers for Disease Control and Prevention say cases are on the rise, but so far, it's the latest start on record. What's happening? Could the flu bug be taking a hit from this warm weather, or could it simply be a weaker strain of flu circulating this season?

Our number is 1-800-989-8255, 1-800-989-8255. And you can tweet us @scifri. We're going to talk a little bit about the flu season first with Dr. Peter Palese. He's professor and chair of the Department of Microbiology at Mount Sinai School of Medicine here in New York. Welcome to SCIENCE FRIDAY.

So what is your take? Is the flu season milder than - as we think it is?

PETER PALESE: Yeah, absolutely. In France this year, this winter season, it's much, much milder than we had it in the last several years. So in a way we are lucky ducks.

(SOUNDBITE OF LAUGHTER)

FLATOW: Let's not get into the bird flu. We are lucky ducks, and is it because it's warmer? Is it the global warming, I guess is what I'm asking, having anything to do with it?

PALESE: Influenza really comes actually in three different flavors. So there are really three different influenza viruses. And we can sort of define what they are. They are two influenza A viruses and one influenza B virus. And the years, actually - or during a particular season, we can have either one of the As or two of the As, and in another year we only one of the Bs.

So there is some unpredictability, and I would rather say that this year, we are just really lucky. I'm not sure whether the warm weather is really the reason for having a much more mellow season in terms of influenza.

FLATOW: But you could argue that, well, if it's warm weather, people are outside, they're not huddled in places keeping warm and maybe not spreading it around. Would that be a valid argument?

PALESE: I think this is a very valid argument, and I'm sure that people will try to sort of get some data on that kind of observation. On the other hand, we had in the past years which were very, very mild, comparable to what we have right now.

FLATOW: And do we have any reason why that was, or it's just how it happens sometimes?

PALESE: Unfortunately, we do not understand the precise mechanisms for that. So there is really a lot of luck involved, a lot of change, and it is really not predictable, unfortunately.

FLATOW: And there's still a lot of winter left, isn't there now? We've got almost a month to go in wintertime.

PALESE: Some of my colleagues sort of bring that up and say maybe there's a second wave. Again, I'm not sure we can predict that. Maybe we are really just lucky, and it will be over.

FLATOW: You had a study in the journal Science this week about the H5N1 strain that's kind of interesting, very interesting. Tell us about what you wrote there.

PALESE: So in terms of the regular human influenza, we talked about the two As, two influenza A viruses, and one influenza B. But there are also avian influenza viruses, influenza viruses which infect particularly chicken but also turkeys, ducks and other poultry.

So this H5N1 virus, which is defined by H - hemoglobin, and the H stands for hemoglobin and N for neuraminidase, is not a human virus in essence. But under certain circumstances, it can actually cause disease in humans. And the paper we just published in Science actually says that there are, particularly in Asia, there are some people who have been infected by such H5N1 viruses without getting really sick.

And that sort of tries to calm down, a little bit, the fear many people have that this H5N1 virus is very dangerous for humans. And it is based on the fact that the WHO has statistics which suggest that out of 600 confirmed H5N1 patients, humans, 300 died.

However, this definition by the WHO, World Health Organization, is a very rigorous one and basically only includes people who have been hospitalized. And then there are samples, blood samples, etcetera, have been sent to the Centers for Disease Control in Atlanta or to the English in London to the WHO center in London.

So yes, this WHO statistics is correct, but it doesn't include many of the - of people who have been infected but who are not clinically ill, who...

FLATOW: Not sick enough to...

PALESE: Who are not sick enough to show up in the hospital. And that was what we published in Science, that there's a much larger number of people who have been exposed to such H5N1 viruses without keeling over and without being - without really having serious symptoms and being - have to be treated in hospitals.

FLATOW: Is the H5N1 synonymous with avian flu?

PALESE: In essence, yes, in essence. H5N1 is the most common avian influenza virus, bird influenza virus. And again, if you are a chicken, it is a very serious virus. In many instances, 80, sometimes 90 percent of the infected chicken all die.

FLATOW: So it affects different animals different ways.

PALESE: Sure, but there are many viruses, many pathogens which in cattle are very bad, but they don't do anything, or very little, in humans.

FLATOW: I'm reminded of the - we were talking today about the spread, how viruses spread around. And if you have a weak strain of, let's say, the flu virus, would it infect other people and actually be a good thing because it's a weak strain, it's infecting other people and giving you some sort of immunity to it later on?

PALESE: I think that's a very good point you make because if we just get a mild infection, we will then be protected against that strain. Unfortunately, with influenza, there is also change. So in other words, if a virus comes back in two years or three years, then that virus is very different, and the protection they acquired by having been infected in February of 2012 is, unfortunately, not good enough, not protective enough.

FLATOW: And they love to mutate, don't they?

PALESE: These viruses are just happily mutating and thereby avoid our immune system - very different from other viruses, and in essence not clearly to explain even by people like myself who have worked for 40 years in this area.

FLATOW: We have a tweet here, for example, from Duke Miller(ph), who says: Here in the state of Missouri, I think everyone has the flu. He was told that: We are the worst in the country. So some - maybe there are these little pockets.

PALESE: There is clearly - I think there's a very good example that there are pockets of influenza where the viruses are spreading much faster than in other areas, and it may have to do with the fact that maybe last year, there was very little flu in that area. And then people, as you pointed out before, may not have acquired that immunity and thus are - in a year where we have very little influenza nationwide, there may be certain states where there's actually more.

FLATOW: Let me see if I can get a quick call in from Diana(ph) in Dearborn, Michigan. Hi there, welcome to SCIENCE FRIDAY.

DIANA: Hi, and thank you for having me.

FLATOW: Go ahead.

DIANA: I was just going to say that I'm a pharmacist, and I work in a pharmacy, and this year more than ever I have - I usually dispense a lot of Tamiflu over the winter season. And this year I've dispensed maybe one or two. And so mainly I have people asking me about allergy medications, if anything, this winter.

FLATOW: Did you give out a lot of flu shots this year?

DIANA: You know, not as much as normal. Usually I do a lot more than I've done in the past.

FLATOW: Because there are some people who are speculating that the reason we're not seeing so many cases of the flu is that a lot of pharmacists dispensed a lot of flu vaccine. But you're saying that's not true.

DIANA: Yeah, I definitely have done a lot, but usually I'll get a big burst during March and - you know, the end of February and March just because it gets colder and people are getting sick, so it hasn't got in much this time. But in fall you usually get a lot.

PALESE: Our listener is very correct, saying that in the pharmacy, if very little Tamiflu - which is an anti-viral against influenza - is being sold, that there is most likely much less influenza in the population.

FLATOW: Thank you, Diana, for calling in.

DIANA: Thank you.

FLATOW: And I hope your rest of the winter goes as well for you.

DIANA: Great, thanks.

FLATOW: 1-800-989-8255. So we have a - are we at the peak of the flu season? Should this be the peak time, where we get reported cases?

PALESE: In general that would be the peak time, but the - never say never.

FLATOW: Does that mean that next year it could really hit us harder because we didn't get it this year? Or is there just no way to predict that, and you could throw a dart at a board and...

PALESE: I think let's not make those predictions.

FLATOW: We don't want to jinx ourselves. Yeah, there's no way to know that. So you're happy, then. I mean, this is a good thing that we're not seeing a lot of the flu and because with the flu comes complications, right?

PALESE: Yes, I mean, it is - we all know the symptoms of influenza - coughing, feeling miserable - but particularly the older ones, the immune-compromised people and the very young ones - always much, much more affected.

FLATOW: And you always hear people complaining I don't want to take a shot because it makes me sick, there's a side effect. Is that mythology?

PALESE: OK, so this is worse than mythology. So our influenza virus vaccines are not perfect, but certainly they cannot, they cannot make us sick. So clearly if you want to get sick, then don't take the vaccine. But the FDA, Food and Drug Administration, approved influenza virus vaccines in this country, absolutely safe, and there is no reason to believe that you can get the flu.

FLATOW: There you have. Dr. Peter Palese is professor and chair of the Department of Microbiology at Mount Sinai School of Medicine here in New York. Thank you, Dr. Palese, for coming in to be with us today.

PALESE: Thank you.

FLATOW: After the break, we're going to talk about a reporter's search for genetic answers about his own genome, that linked to some scary revelations. So stay with us. We'll be right back after this break.

(SOUNDBITE OF MUSIC)

FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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