Why the New Flu Matters

Take a look at this image. It isn't all that much to look at, but that is what the influenza virus looks like up close and personal. This photo comes courtesy of the Public Health Image Library at the Centers for Disease Control and Prevention. And this little bugger is what has had most of us in my profession running on high alert since the end of March.

I am a the Food Borne Disease epidemiologist for the State of North Carolina Division of Public Health. But before that, I was a general infectious disease epidemiologist with the Texas Department of Health in Austin, Texas. There I worked as much on respiratory diseases like tuberculosis, Legionnaire's disease, and influenza as I did on enteric pathogens like cryptosporidium, salmonella and E. coli. In the late 1990s I was the influenza surveillance coordinator for the State of Texas. So when this novel strain of influenza (H1N1) popped up, I was extremely interested. And, as it turned out, I was also on call that first weekend it hit in the U.S., and wound up working as part of our response team on this issue for the past several weeks.

I know that a lot of people think the hype over novel influenza this past month was overblown, and I have read the same snarky comments that everyone else has about this all being much ado about nothing really important. That could not be further from the truth. And for everyone who thinks this has all blown over, I'm sorry, but this has not even started yet for us here in the U.S.

For the past several years, we in public health have been sounding warning bells that the world is overdue for an influenza pandemic. Pandemics are world-wide epidemics of disease occurring simultaneously or in close succession, caused by the same organism. Very few pathogens are capable of causing pandemics. Influenza is one that not only can, it does. In the past century there have been three major pandemics: 1918, 1957, and 1967. Most of us don't remember them, although I was 3 years old in 1967 and lived through it. The worst one of course was 1918 when more than 40 million people died world-wide. We really don't know how many people died, because there are no accurate records from that era for places like India and China.

Pandemic influenza is caused when a novel virus emerges, usually due to reassortment of genetic pieces from a combination of influenza viruses that can infect both humans and animals. There are many different kinds of influenza viruses. When a host organism gets infected with two or more virus strains at the same time, the genes can get scrambled and a new virus emerges. That creates what is known as a shift virus, which is different from the genetic drift we see with influenza from one annual epidemic to the next one. With drifting viruses, the changes from one year to the next are subtle and can be mild. People who have been exposed to a prior version of the virus may have partial immunity, and they don't get as sick. Herd immunity from the general population keeps the numbers of newly infected people down as well.

Shift viruses are different. With shift viruses, everyone on Earth is susceptible to them. No one has the benefit of prior infection, so the numbers of new cases are likely to be higher. Sometimes the illnesses can also be much worse. The annual influenza epidemic in the U.S. infects anywhere from 5%-20% of the population. With shift viruses, we can expect the numbers to be higher--but not until next flu season, when this virus should return as the dominant strain causing illness in the U.S. Right now the new virus is a minor player. Next year, this one is likely to steal the show.

For the past several years the World Health Organization has tracked a different new influenza virus, the avian influenza H5N1 virus. That one is a bad actor, with a 60% mortality rate. But it does not transmit easily from person-to-person, and even though we have tracked it since 2003, so far it has only caused 424 confirmed human infections with 261 deaths (as of May 15, according to WHO). That is after six years. This new influenza H1N1 has caused 8,480 confirmed cases in 39 countries with 72 deaths since March 2009. (As of May 17, according to WHO). It is less than two months into this virus. It is moving much more easily, and since everyone is susceptible, it should become well established. This one is not going away and it has already taken flight.

So, yeah, we have been overdue for a pandemic for a long time. It is looking like we will soon have one on our hands, if we don't already.