In recent years, seasonal flu outbreaks peaked in February or March, filling hospitals and medical clinics with people aching from the respiratory illness.
But this has been a strange flu season.
The H1N1 pandemic, which sickened Stanislaus County residents starting in the summer and swept through schools in the fall, has nearly disappeared in Northern California. And there are almost no signs of seasonal flu strain outbreaks in the region.
Less than 1 percent of the respiratory test samples taken at Kaiser Permanente clinics have been positive for H1N1 in the past five or six weeks, said Randy Bergen, clinical lead for Kaiser's Northern California flu vaccine program.
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"There is almost no seasonal flu activity," he added. "That leads me to question whether we will see seasonal influenza this year."
Bergen said he could only guess why the seasonal flu strains are leaving people alone. It could be the H1N1 virus was so dominant "it hasn't given an opportunity for the seasonal viruses to circulate," he said.
The break comes as a relief for the general population, which watched as H1N1, or swine flu, emerged in Mexico in April and then swept the world.
Stanislaus County recorded 13 deaths and 202 people hospitalized from complications of the novel flu strain. The last death in the county came in the third week in December, and no one has been hospitalized since the second week of January.
It's called a pandemic, but H1N1 has not been as lethal as previous pandemics. Health agencies reported 553 deaths in California, which has about 4,000 deaths from seasonal flu each year.
Dr. John Walker, Stanislaus County's public health officer, believes there is still a chance for another wave of H1N1. His opinion is shared by experts at the federal Centers for Disease Control and Prevention.
The three flu pandemics of the past century ran their course over an 18-month period and circulated in three waves, Walker said, noting this is the 10th or 11th month of the H1N1 scourge.
"The reason a pandemic ends is there is sufficient global immunity either from infection or vaccination," Walker said. "We are clearly past the second wave, but at best, we are two-thirds of the way through this."
Walker said he doesn't believe government health agencies overreacted to H1N1.
In Walker's opinion, the virus was not so lethal because it primarily affected younger adults and children, who were strong enough to get over the infection. Most of those who die from seasonal flu are older people in frail health.
Public health agencies were concerned that if people were infected with both H1N1 and seasonal flu strains, the strains could form a new virus that would threaten the senior population, Walker said.
One failing of the public health response was the shortage of H1N1 vaccine until after the holiday season, when public concern about the virus had waned. The shortage was caused by manufacturing delays as drug companies switched from production of seasonal flu vaccine to the H1N1 variety.
The county Health Services Agency administered about 10,000 doses of the swine flu vaccine at free public clinics in January, less than half the number of seasonal flu shots given in the fall.
The health agency received 45,150 doses from the federal government for holding community and school-based vaccination clinics. The school districts in Turlock, Ceres and Patterson gave vaccinations to about 6,000 students.
The county health agency still has a plentiful supply and has a nurse working to give the shots at the immunization clinic on Scenic Drive in Modesto. Walker said the federal government, not the county, paid for the vaccine.
A more limited supply of H1N1 vaccine was delivered to the county in the fall, and Walker's office directed those supplies to health care providers in the community. Walker defended the decision, saying the intent was for private physicians and health clinics to give the vaccine to high-risk groups, such as children, pregnant women or people with chronic illness.
As a result of the decision, none of the vaccine went to pharmacies or other groups that provide flu shots to the general public. Some parents of children with asthma or other health issues complained it took too long to get vaccinations from their health care providers.
"We made a collaborative decision with the (Stanislaus Medical Society) that doctors make the best decisions about giving the vaccine to high-risk patients," Walker said.
Bergen wasn't predicting another wave of H1N1. Because of its vast number of medical clinics, Kaiser is able to do extensive monitoring for flu strains in California.
"Certainly, I continue to be concerned there may be a third wave, but at this point there is no evidence this is happening," he said.
The CDC has selected H1N1 as one of the strains targeted by seasonal flu vaccine to be manufactured for distribution in the fall.
Bee staff writer Ken Carlson can be reached at email@example.com or 578-2321.