The current flu season has produced overcrowded emergency rooms and medication shortages. CDC officials say there are a number of reasons for the flu’s severity this year.

Just weeks into the new year, health officials are grappling with a flu season so severe that there have already been regional shortages of antiviral medication and emergency room wait times have skyrocketed.

In San Diego, a hospital reportedly set up a tent to help handle the influx of patients with influenza symptoms. In Arizona, the health department warned that ER wait times were so long, people shouldn’t look for emergency care unless they’re having severe symptoms or are a high-risk patient.

“People with mild symptoms or at lower risk from complications from influenza should stay home and rest or call their healthcare provider,” the Arizona Department of Health Services said in a statement.

Today, the U.S. Centers for Disease Control and Prevention (CDC) reported that flu activity is widespread in 49 states and that the season has arrived earlier than normal.

During a grand rounds presentation for medical experts, CDC officials explained in part why the flu season is severe. This year, the dominant strain is an influenza A strain called H3N2. First appearing in humans in 1968, this strain is associated with worse outcomes for people who contract it. In the past, it has led to a higher number of flu infections and hospitalizations.

Dr. Daniel B. Jernigan, MPH, the director of the influenza division in the National Center for Immunization and Respiratory Diseases (NCIRD) at the CDC, said they’re seeing a high number of flu cases earlier than expected. At least 26 states have reported “high” flu activity, and 10 other states have reported “moderate” flu activity.

“Flu is in lots of places at the same time,” he said. “Simply because of where it’s occurring, which is everywhere.”

At least 20 children have died from the flu so far, Jernigan said.

Dr. Alicia Fry, MPH, chief of the epidemiology and prevention branch in the NCIRD and a captain in the U.S. Public Health Service, explained that once people are infected with flu, there’s little medical officials can do, except to give them antivirals. These can shorten the duration of symptoms by a day.

“Right now, there is an adequate national supply to meet the high demands of the season,” she said. However, she cautioned that “spot shortages have been reported in areas with high influenza activity.”

Fry said health officials are working with antiviral manufacturers to bridge gaps in availability.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, said one potential reason the flu season has been intense this year is due to the fact that the flu season started early.

As a result of starting early, the flu season coincided with “the holidays, travel, family reunion season, so that holiday travel acted as a great mixer,” he said.

“We think that that was a major contributor to the blooming of the flu” across the nation, he explained.

Schaffner said the influenza season puts additional strain on hospitals, which increasingly lack extra beds for patients.

“Our hospital bed capacity in the U.S. — at least in the urban areas — is pretty finely calibrated,” he said. The number of occupied hospital beds can fall short of what’s needed during an outbreak “because our built capacity has been constrained by all kinds of financial considerations.”

As a result, he said he knows of hospitals where patients have to remain on gurneys in emergency room hallways because there are no free beds for them.

Schaffner also said that despite years of research, experts still haven’t confirmed why flu infections tend to happen in winter months. One likely reason is that in cold months, people congregate together indoors, where viruses can easily spread. He said the flu virus spreads even in parts of the country that are relatively warm.

Schaffner added that another explanation is lack of humidity in winter months, even in relatively warm states in the South. He said the flu virus spreads by attaching itself to small droplets that are transmitted from the respiratory system of one person to another via coughing, sneezing, or just talking.

“When humidity is low, you breathe out that droplet and that moisture evaporates, and the tiny microscopic particle is light and it stays suspended in the air,” he said of the virus particle. As a result, it’s in the air longer, meaning it increases the likelihood another person will “breathe it in and get infected.”

Dr. Sunil Sood, chairman of pediatrics at Southside Hospital in New York and an infectious disease specialist, said it’s key that children especially get their flu vaccinations.

Kids are the spreaders to elderly people, so it’s important that all kids “over 6 months get the flu shot,” he said. “To protect the rest of the population, you need to immunize every child in the country. There’s really no downside to getting the flu vaccine.”

Sood said that data showing the flu vaccine to have low effectiveness — in one Australia-based study to be just 10 percent effective — may lead people to decide that getting a flu shot isn’t worth it.

But he said the medical community needs to combat that notion by talking more to patients.

“I think we lack effective messaging on the meaning of the vaccine effectiveness,” he said. He explained that even if a flu vaccine is just “32 percent effective,” it means that a person has a “32 percent less risk” of needing to get medical attention for flu symptoms.

“I would take a 1 in 3 chance that I don’t have to go to the doctor,” he said. “Nothing is perfect.”