One year ago this week the world suddenly woke up to a new threat. A novel flu virus had arrived on the scene.

It was a virus the world had never seen before, one that would later be called H1N1.

At first there were more questions than answers: How serious was the disease this new virus was causing? How fast would it spread between people? Was it treatable with drugs? Could a vaccine be developed to stop it?

The earliest reports said the virus was responsible for widespread disease in Mexico. Laboratory-confirmed cases had also turned up in California and Texas.

And then, just a day after we first heard about the virus, the first American cases away from the border were found right here in Kansas.

And across the country, millions of people started to take hand washing and "cough etiquette" seriously for the first time in their lives.

At first, actual cases of the new flu were rare. But talk about the emerging pandemic was everywhere, from cable newsrooms, to the halls of Congress, to kitchen tables in every community.

A year later, most of the talk about H1N1 flu has disappeared.

Although the virus remains present in every state, and is likely to kill thousands of Americans in the coming flu season, most Americans no longer give serious thought to H1N1 influenza.

That's unfortunate, because now is a good time to take stock of what we have learned about H1N1 flu in the past year, and start to prepare for the unpredictable but inevitable next chapter in humanity's ongoing coexistence with this new virus.

Most Americans remain susceptible to H1N1 flu. Of the 309 million residents of the United States, about 60 million were naturally infected during the past year and 75 million got the vaccine (some of whom may also have been infected). That leaves at least 174 million, or 56 percent of the population, still vulnerable.

Influenza viruses typically mutate from year to year. Although the H1N1 virus has been relatively stable so far, we can expect it to change over time. This means that people who were infected and/or immunized in the past flu season may become susceptible again. Everyone will need to get the new flu vaccine coming in the fall, with repeat doses every year after that.

The virus has already shown it can kill more than 12,000 Americans and has put 270,000 others in the hospital, including many young people who are not normally sickened as seriously with the flu.

Influenza vaccines work and are very safe. Although production difficulties prevented full deployment of the H1N1 flu vaccine as rapidly as was first hoped, the brisk uptake of the vaccine in every community nationwide dampened the explosive growth of the epidemic during the fall of 2009 and is likely to have prevented another pandemic wave during the winter months of 2010.

No one is talking about it anymore, but the H1N1 flu pandemic isn't over.

It's a safe bet that case numbers will rebound sooner or later. Will you be ready?

DR. JASON EBERHART-PHILLIPS,

Topeka

Dr. Eberhart-Phillips is the Kansas State Health Officer and Director of Health in the Kansas Department of Health and Environment.