For most of the season, the H1N1 flu strain has dominated, but now a stronger H3N2 strain appears to be taking over. During the week ending March 9, 2019, the Centers for Disease Control and Prevention (CDC) found that 61 percent of new influenza A cases were H3N2. The CDC’s latest report also indicates widespread flu activity throughout 48 states and Puerto Rico, with the most H3N2 cases in the Southeast (Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee). William Schaffner, MD, an infectious disease specialist and professor of preventive medicine and health policy at the Vanderbilt University School of Medicine in Nashville, Tennessee, warns that this new strain could keep flu season active well into April and possibly May. Even people who have already had the flu may need to take extra care against getting the flu again. “There’s usually a dominant influenza strain throughout a season,” says Dr. Schaffner. “But now the virus that’s causing the most cases has flipped from H1N1 to H3N2. That’s a big surprise because you usually don’t have a sequence of two dominant viruses in one season.”
A More Dangerous Disease
Overall, symptoms of both flus are similar and include cough, sore throat, runny nose, congestion, headache, body pains, and fever. H3N2, however, typically leads to more serious illness and hospitalization compared with H1N1. During the winter of 2017–2018, when H3N2 prevailed, the CDC reported that more than 80,000 people died of influenza in the United States, making it one of the deadliest flu seasons in decades. So far this year, the CDC estimates flu-related deaths between 21,500 and 35,500. Up to 29.3 million have had flu illnesses this season, compared with the CDC’s report of 48.8 million last year. “H3N2 seems to be a more virulent strain, causing more severe illness compared with H1N1, including a greater incidence of respiratory infections such as pneumonia,” says Robert Glatter, MD, a physician in the department of emergency medicine at Lenox Hill Hospital in New York City.
Still Time for a Protective Shot
Traditional flu vaccines (called “trivalent”) are made to protect against H1N1 and H3N2 as well as less-common influenza B viruses. Vaccination antibodies require about two weeks in the body to take effect. Although a vaccination in the fall — at the beginning of the flu season — may offer the longest protection, the CDC says that a flu shot now can still be beneficial as the illness continues to circulate through communities. “Patients should understand that it’s never too late to get the flu shot,” says Dr. Glatter. “We vaccinate patients year-round.” The CDC recommends that everyone age 6 months and older should get the vaccine annually. The health agency stresses that the shot is especially vital to the health of those who are at high risk of developing flu-like complications. These include children under age 5, adults 65 and older, pregnant women, and residents in long-term care facilities. Individuals with certain medical conditions are also considered high risk. These ailments include asthma, emphysema, chronic lung disease, heart disease, diabetes, immune-related sickness, cancer, as well as liver, kidney, and blood disorders. To help ensure protection from illness, the U.S. Department of Health and Human Services advises people to steer clear of those who are already sick, wash hands regularly, keep surfaces clean, and avoid touching your nose, mouth, and eyes. An antiviral medication, such as Tamiflu or Xofluza (baloxavir marboxil), can shorten the duration and severity of the influenza, but these drugs work best if they can be started within the first 48 hours of illness onset. “This second strain is arriving very late in the flu season, and none of my colleagues at the CDC have an explanation why this is happening. They’re all scratching their heads,” says Schaffner. “It just goes to demonstrate that flu may do something a little different every year, and you have to be aware and protect yourself.”
