Although experts are not sure to what degree, seasonal flu cases and deaths dropped in Maryland and nationwide this year, during the height of the novel H1N1 pandemic.
While flu cases are not perfectly tracked, epidemiologists believe the decreases were caused by increased health campaigning and vaccination rates, a weaker seasonal flu strain, and other causes.
Epidemiologists all over the world think next flu season's primary strain will mutate around H1N1, or swine flu. Although officials and health professionals do not know how strong the 2010-2011 flu season will be, they are encouraging vaccination.
"Overall flu deaths are down this year because H1N1 flu crowded seasonal flu out," said Jeff Dimond, a health communications specialist for the federal Centers for Disease Control and Prevention. "But this is a drastic oversimplification."
According to a study in the Journal of the American Medical Association, about 36,000 Americans die from seasonal flu in an average year. That would translate to about 600 to 1,000 people in Maryland.
This year, 45 people in Maryland and an estimated 12,000 people in the United States died from novel H1N1.
Of all the flu samples tested this season, only seven, or less than 1 percent in Maryland, and 394, or about 1 percent nationwide, turned out to be positive for non-novel H1N1 seasonal flu strains.
Nationally, more than 22,000 samples were not categorized during testing due to bad quality of the sample and lack of equipment, among other reasons.
But epidemiologists believe the proportions of novel H1N1 and seasonal flu are correct. There are still deaths being reported and recorded by the state and the Centers for Disease Control and Prevention.
The estimates are important because the actual data is so vague. Hospitals are required to report only seasonal flu deaths of children or health care professionals to the Department of Health and Mental Hygiene, even though the elderly typically account for 90 percent of estimated seasonal flu deaths.
"An example of why this is would be an elderly person who contracts seasonal flu. This individual may have other health issues, such as cancer or diabetes or renal issues, the flu then morphs into pneumonia and the patient dies. Did the patient die of flu, pneumonia, cancers or complications from other health issues?" Dimond said via e-mail.
It is also important to note that every year's numbers for deaths and hospitalizations due to the seasonal flu are underreported because not everyone who receives medical attention receives a test to verify whether they had flu.
Ninety percent of people affected by novel H1N1 are younger than 65.
Swine flu numbers are not perfect either, said Trish Perl, director of hospital epidemiology and infection control and hospital epidemiologist at Johns Hopkins Hospital. Up to 50 percent of initial swine flu cases were not identified early on due to lack of technology.
Novel H1N1 is technically one strain of the overall seasonal flu, but because most people had never been exposed to it, it was categorized as a pandemic.
Epidemiologists have not seen a similar strain since the 1950s. The elderly are therefore less susceptible to parts of the novel H1N1 strain because they have remnants of immunity from earlier in their lives.
Even though novel H1N1 is genetically mutated, it might be mistaken for seasonal flu. Symptoms also include cough and fever.
There are many possible reasons for the drop in deaths.
Due to the H1N1 pandemic and the late creation of the vaccine, there was more publicity in place earlier on how to protect against the flu.
The tips "were really heavily promoted because it was the only measure people could take at the time," said Frances Phillips, Maryland's deputy secretary for public health services.
Working from home was encouraged by many companies if an employee believed he was sick. Weather also might have played a hand, Perl said. It stayed warm until late fall, making the virus unable to be transmitted as easily.
Another explanation could be an increase of seasonal flu vaccinations because of H1N1. When the swine flu vaccine was in short supply, people got the next best treatment.
But even those who were not vaccinated this year got lucky. The primary seasonal flu strain has not mutated significantly during the past three years, meaning that previous vaccinations could have protected against this year's strain.
Getting H1N1 also could have acted as a shield against seasonal flu. People's natural defenses would be on high alert if they already had swine flu. For some, though, it was possible to contract both seasonal and swine flu.
The seasonal flu strain could also have been weaker this year, making it less infectious.
Epidemiologists in the United States and at the World Health Organization think that novel H1N1 is going to be one of three viral strains to mutate into the new dominant strain, making them unsure what to expect from the upcoming flu season.
The CDC's Advisory Committee on Immunization Practices recommends that everyone six months and older get vaccinated for the coming flu season. This includes the normally exempt age group of 19 to 64.
The Maryland Department of Health and Mental Hygiene will be reaching out to at-risk groups and educating people about safety measures against all flu strains.
"It's impossible to predict [impact] because this is an unusual year. The way I see it, this is history unfolding and nature unfolding," said Lucy Wilson, chief of the Center for Surveillance, Infection Prevention and Outbreak Response at the Maryland Infectious Diseases and Environmental Health Administration. "We hope, given that people were exposed to H1N1 this year (and certain public health measures) were taken, it will help lessen the impact."