After four students at Marion Earl Elementary School were diagnosed with swine flu earlier this month, hundreds of parents, fearful that their children might be exposed to the virus, kept their children home.
Others, including Vinnie Cervoni, whose 6-year-old son Giovanni attends Earl, agonized over whether they were placing their children in harm's way by sending them to school.
It is the kind of parental concern seen nationwide.
But strange as it may seem, exposure to the flu strain might have a hidden benefit.
"There may well have been a silver lining for those who were exposed or even became ill with an illness that has generally been milder than the seasonal flu," said Dr. John Middaugh, director of community health for the Southern Nevada Health District. "They could be immune from it this coming flu season."
Even if the H1N1 virus mutates into a more virulent form, as many researchers fear, previous exposure does give a person "partial immunity," said Dr. Mary Guinan, the state's health officer.
"We have found that there is some crossover immunity even when they (viruses) mutate," Guinan said.
That physicians now publicly speak of a possible benefit to swine flu exposure illustrates just how fluid public health investigations can be.
In late April, the Centers for Disease Control and Prevention advised officials to close schools for up to two weeks if students were infected with swine flu, advice seconded by President Barack Obama in a televised plea.
By May, the CDC guidelines had changed after American researchers determined that reports of healthy young people quickly dying in Mexico from the disease were erroneous.
That information, coupled with the fact that swine flu had quickly spread into communities throughout the United States, made school closures ineffective in controlling the virus, Middaugh said.
"There is no evidence that closing a school prevents spread of the disease," Guinan said.
Yet Guinan stressed that no parent can be blamed for trying to protect a child from sickness.
A child might have an underlying medical condition that could make even a mild flu like the H1N1 strain dangerous, she said.
But she also pointed out that the current outbreak has shown how immunity can change how the flu spreads through the population.
As the swine flu spreads across the United States, fewer than 1 percent of the cases are in people older than 65, even though the elderly remain the group most susceptible to typical seasonal outbreaks of influenza.
The best explanation for this seeming contradiction came in late May from CDC researchers who had tested stored blood samples from various age groups for antibodies to the new H1N1 strain.
"Results among adults suggest that some degree of pre-existing immunity to the novel H1N1 strains exists, especially among adults aged over 60 years," they said in a report.
Researchers suggested that many older adults were either infected with or vaccinated against an older seasonal flu strain that closely resembles H1N1.
Guinan said parents have dealt with the question of immunity and disease for years. Before there were vaccinations for diseases such as mumps or chicken pox, Guinan said parents actually hoped their children would get it while they were young so they would have immunity and not catch the virus when older.
"They knew that it was much more serious to get those diseases when you got older," she said.
When a new H1N1 vaccine becomes available, Middaugh said ideally it would be good to know who already has immunity.
That would be particularly useful if the vaccine was in short supply, he said.
But he said that ideal situation, involving taking blood samples from everyone and testing them, would be both time and cost prohibitive.
Middaugh stressed, however, that it wouldn't be a problem for a child who has already recovered from the new flu strain to get vaccinated.
"That child already would have the best immunity, and the vaccination would be like getting a booster," he said.
Contact reporter Paul Harasim at firstname.lastname@example.org or 702-387-2908.