Avian flu surveillance efforts. Credit: Province of British Columbia

For the first time, a new strain of bird flu was transmitted human-to-human. This is highly unusual–and could be the first sign of new global pandemic.

In 1918, the world was rocked by pandemic flu. A virulent strain of influenza, H1N1 influenza swept across the whole planet. A fifth of the world’s population was infected, and 20-40 million people died. It killed more people than World War One.

We haven’t seen pandemic influenza on that scale since then, but it’s been because of luck, not skill. Our globalized world is actually at a greater risk for pandemic than we were in 1918. Thanks to air travel, people travel farther, faster, and more often than they did a century ago. In just the last decade, we’ve seen Ebola cross borders, Zika infect a new continent, and a 2009 H1N1 pandemic that had a thankfully, inexplicably, low mortality rate.

So far, however, we haven’t seen a truly devastating flu epidemic in humans. Mild forms of the flu have been very contagious, and do routinely cross borders and infect large numbers of people, but they’re mild. People get unpleasantly sick, and the very young and very old may die, but the mortality rates are not unusually high. At the same time, we’ve experience some very deadly forms of the flu. Avian influenza, known as H7N9, kills 40% of people who are infected. That’s a mortality rate to fear – H1N1 had a mortality rate of 2-5% in 1918. However, avian influenza is not contagious from person to person – it spreads bird to person.

The pandemic of 1918 was both highly contagious and highly deadly. We haven’t seen that in the last hundred-something years.

Which brings us to last week, when a Chinese medical journal reported a human-to-human transmission of H7N9. H7N9, as mentioned, has a mortality rate of about 40%. Its impact on humans has been mitigated by the fact that it only spreads from birds. Family members can care for each other without fear.

Last week, though, China reported a case of H7N9 that appears to have spread person to person, not bird to person. The infected patient had no contact with birds or live bird markets, and he had no underlying medical condition. He was a healthy 62-year-old man, who helped a family member hospitalized with H7N9 to use the bathroom. Genetic analysis of the infecting virus indicates that he was infected with the same strain of virus that infected his family member.

This could be a sign that H7N9 is evolving into a virus that spreads among people. A highly contagious virus that has a 40% mortality rate. By way of comparison, Ebola is a highly contagious virus with a 50% mortality rate that spreads among people. There is serious potential here for global catastrophe.

It’s not doomsday yet. Helping someone use the toilet is a very intimate act; that means a contagious virus, but not necessarily highly contagious. Spreading in that kind of close quarters does not mean it will spread in schools or markets. And according to the epidemiological report, “There were a lot of family members in the ward, but he was the only one who was in close contact with the index case, and he was the only one confirmed H7N9.” So even being in the same room with an infected person does not necessarily mean infection.

The WHO has called for increased surveillance efforts for H7N9, but it isn’t quite ringing the alarm. While these human cases are a sign of an evolving virus, it hasn’t so far evolved into the  danger zone. Their analysis states that “current epidemiological and virologic evidence suggests that this virus has not acquired the ability of sustained transmission among humans. Therefore the likelihood of further community level spread is considered low.”
 The US Centers for Disease Control and Prevention (CDC) is less certain. According to acting director Anne Schuchat, “This one hasn’t (evolved) yet.  But that’s why we’re keeping our eye on it. Because it has the capacity to evolve and change.”

If you’re watching viruses, though, you’re watching this one.