As schools across the country start the academic year, many questions remain on the minds of parents who are considering having their children vaccinated against the H1N1 flu virus.
H1N1 has infected well over 1 million people in the United States, and it is now the CDC's No. 1 priority. The World Health Organization predicts a third of the world's population will eventually be infected.
Not surprisingly, you may have a lot of questions. We’ve done our best to answer them.
Who’s at risk?
Every year, seasonal flu infects between 5 percent and 20 percent of a given population and kills between 250,000 and 500,000 people globally. But unlike seasonal flu, research shows that older children and young adults are by far the most likely to be infected with the new H1N1 virus.
“Flu viruses change every year, so the people who have been around longer and have been infected with other H1N1 flu viruses probably have a partial immunity to this new virus that’s circulating now,” said Dr. Peter Gross, senior vice president and chief medical officer at Hackensack University Medical Center in New Jersey.
Partial immunity means that they may still get infected with the flu, but they would be less likely to be in the hospital or have severe consequences, he added.
Doctors are recommending that patients who fall into high-risk categories get vaccinated, including those with chronic illness, heart disease, lung disease, diabetes or suppressed immune systems, people between 20 and 40 years old, pregnant women and infants.
Why get vaccinated?
Flu is one of the most complex and confusing of all viruses. Others, like measles, stay the same year after year. But because there are so many variants and sub-types of influenza, people have to get vaccinated yearly because every one to three years, influenza viruses mutate.
Each year, health officials decide in January or February which flu strains will be included in the seasonal flu vaccine. But there is a chance that by the time it becomes available in September, the viruses may have changed.
“It happens every few years with the influenza,” Gross said. “But when it does happen, there is still some protection from the vaccine, so it’s always worthwhile to get vaccinated, because at least you’ll have partial protection. And H1N1 strains of the flu virus change less often.”
This flu season, there will be two vaccines available: the standard seasonal flu vaccine, which protects against three different strains of the virus, and new H1N1 vaccine.
“For most people under 50, they’ll need two shots of H1N1 vaccine three-to four weeks apart,” said Gross. “So their immune system will be primed with the first shot and completed with the second shot.”
What are the side effects?
Like the seasonal influenza vaccine, the side effects associated with the H1N1 flu vaccine should be minimal.
“The main side effect is soreness at the injection site, and sometimes you may feel achy, but you can always take Tylenol,” Gross said. “You don’t want to take aspirin during an influenza epidemic because there have been reports of Reye’s syndrome in people who become infected and take aspirin.”
What about Guillain-Barre syndrome?
Guillain-Barre syndrome is a rare disorder where the body’s immune system attacks the nerves, causing weakness and numbness to the arms and legs — and sometimes even paralysis.
Many Americans are concerned about the safety and efficacy of the newly developed H1N1 flu shot because of a similar vaccine that was linked to a swine flu-like outbreak at Fort Dix in 1976.
In 1976, when 40 million people received the H1N1 vaccination over a period of a few months, the incidence of Guillain-Barre syndrome was about one out of 150,000, Gross said. This compares to about 1 in a million people who develop the syndrome from the seasonal flu shot.
Guillain-Barre occurs naturally following upper respiratory illnesses, digestive illnesses and is rarely associated with some drugs and vaccines, he cautioned. But he said the fear of Guillain-Barre syndrome would not prevent him from giving most vaccines — including the seasonal influenza vaccine.
The new H1N1 vaccine is being vigorously tested before it will be dispensed to the public, which should guard against a similar Guillain-Barre outbreak this time around. However, what, if any, rare side effects will occur will be unknown until hundreds of thousands or even millions of people have received the vaccine, Gross said.
So what are my options if I don’t want to get vaccinated?
Pregnant women, children and teens are at extreme risk for dangerous H1N1 complications, including death, and should be vaccinated no matter what.
Others, however, may have some leeway to play with.
If you had a documented case of H1N1 during the 2008-2009 flu season, you probably have partial immunity. But if the strain changes between now and December, you could be susceptible to contracting the new virus without any immunity.
Many people who were around during the swine flu outbreak in 1976 have been found to have an immunity to H1N1. Also, people over the age of 50 who have been getting an annual flu shot for most of their adult lives (all flu shots contain some form of the H1N1 virus) also appear to have partial immunity.
On Sunday, health officials reported that an estimated 10 percent of the population in New York City was infected with the virus in the spring. While not all cases of H1N1 flu virus were documented, some people may be surprised to find that they have partial immunity when the virus re-emerges as predicted in the fall.
And if you think you may fall into that category, there are ways to find out.
If you had flu-like symptoms in the spring but weren't diagnosed with H1N1, you can get tested to see if the virus antibodies are in your system. There are labs that can test to find out if you are immune to this strain or a previous strain — but you’ll have to pay out of pocket.
Doctors strongly advise getting the seasonal flu vaccine because while a resurgence of the H1N1 flu virus may be on the horizon, there may be other strains of flu making their rounds, and you don’t want to leave yourself susceptible to them.
Reuters contributed to this article.
Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. For more information on Dr. Manny's work, visit AskDrManny.com.