PHOENIX — Health officials said Thursday that the swine flu, which never quite disappeared from Arizona, is coming back in a big way.

The only question that remains is how virulent the second wave will be.

State Health Director Will Humble said not much should be made of the declaration by the World Health Organization officially declaring a “pandemic,’’ the first such flu designation since 1968. He said that designation comes simply because the virus has spread so far and wide.

And Maricopa County Health Director Bob England, is there is no evidence yet that the virus, which continues to infect Arizonans, is any more severe now than it was when first reported several months ago.

“But we’re pretty sure based on the history of every past pandemic that this is going to come back with a second wave that’s bigger,’’ England said. He said that could occur as early as this fall, though for planning purposes, health officials are hoping it holds off until the winter “when we usually get our regular flu season.’’

Simply put, England said that means a lot of Arizonans are going to get sick. But he said the fact that this new strain has so far been no more dangerous than the typical flu doesn’t mean it’s going to stay that way.

“Past pandemics, you get sort of small sub strains, pockets of virus that change in terms of how sick they’re making people,’’ he explained.

“You have to watch that closely so that you can deal with it should the predominant strains, the ones we’re having here, do make people sicker over time.’’

The good news, England said, is that there still is time to plan for what promises to be a more widespread — and possibly more toxic — second wave. And he said that planning has to start at home.

England said individuals should have arrangements for who will take care of them if they become ill and families need to figure out who cares for a sick child. But he said parents also need to consider how they will handle a situation where the health department shuts down a school and sends all the children home for several days or more, as they did earlier this year.

“Who’s going to stay home with the children?’’ he asked.

And England said even businesses need contingency plans should a large number of their workers call in sick.

For the moment, he said, there is no vaccine that has proven effective against this H1N1 variety, with none anticipated for at least several months. But England said that should not stop Arizonans from going to their health care providers to get vaccinated for the regular seasonal flu, a vaccine he expects to be available soon.

He said it won’t provide protection against the swine flu. But health officials hope to get enough people vaccinated against the regular flu to create a “herd effect’’ to prevent it from spreading the way it normally does each year.

And that, England said, will give doctors, nurses and hospitals more time to deal with those infected with swine flu.

Unlike some years, when vaccines are marketed largely to those most vulnerable like the elderly, England said the big push this year will be to inoculate children.

“Children are the main amplifiers of the flu every season,’’ he said.

“Kids spread it very well between each other to other kids and bring it home to more susceptible people at home,’’ England explained. “Every flu season you see the first signs of influenza picking up in the school setting.’’

All that, he said, is trying to create a “herd effect.’’

“If we get enough people immunized who are the people who most transmit the virus to others, then you can decrease the amount of spread of regular seasonal flu down to the point where it will take a big load off the health care system, as well as keeping people who are susceptible to regular flu safe,’’ England said.

He said the normal rules of dealing with flu continue to apply to swine flu: Wash your hands, cover your mouth when you cough and stay home if you’re sick.

And once the swine flu vaccine becomes available, get the shot — or two if that’s what will be required.

But he said there is no reason for Arizonans to hunker down and stay home.

“We have plenty of this new flu right here in Arizona,’’ he said.

“You can get exposed right here,’’ England continued. “You don’t have to go someplace exotic.’’