In the last week of 2017, San Diego's flu season had killed 34 people and reached near epidemic levels — indicating to California health officials this may be one of the most serious flu seasons since the 2009 H1N1 pandemic.
But California isn't alone. While most Americans were traveling and visiting family between Dec. 24 and Dec. 30, 2017, data from athenaInsight's 2017 – 2018 Flu Dashboard showed that 4.34 percent of more than 1 million outpatient visits across the country were coded for influenza-like illness (ILI). This is more than double the percentage at the same time last year, when clinicians reported 2.07 percent of patients had ILI.
This data confirm the latest estimates from the Centers for Disease Control and Prevention, which reports that each of the 10 regions of the United States, ILI outpatient levels are more than double the 2.2 percent national baseline. The flu is now widespread in 46 states, with 26 states experiencing high ILI activity.
'A striking surge' in hospitalizations
Researchers say this year's season started two to three weeks earlier than usual in hotspot regions of the south and west. Across the athenahealth network, especially high rates were seen in Texas for December, at more than 9 percent. Director of the National Institute of Allergy and Infectious Diseases Anthony Fauci told NPR that this early intensity can be an indication of “a serious season."
William Schaffner, M.D., an infectious disease specialist at Vanderbilt University Medical Center, says athenahealth's data reflect what his organization is seeing in hospitals. Vanderbilt Medical Center is one of 12 local surveillance systems established by the CDC that monitor hospitalizations for lab-confirmed influenza.
“We've seen a striking surge in hospitalized influenza cases in the last three weeks," says Schaffner. The CDC reports that 13.7 per 100,000 people have been hospitalized for lab-confirmed influenza in the 2017/2018 flu season so far.
This flu season has really taken off compared to recent years, he says. “It's still going up — this is definitely not the peak for this flu season." Last year the flu started much later into January, peaked in late February, and continued into April and May.
“Flu is fickle and hard to predict," says Schaffner. “We always say that if you've seen one influenza season, you've seen one influenza season."
While there are always multiple strains circulating, this year's dominant strain — H3N2 — has been making people sicker than usual, especially the elderly who are the most vulnerable. The H3N2 strain is also one of the most difficult to vaccinate against.
Fighting vaccine skepticism
Clinicians and public health officials are fighting against a headwind this year to get people vaccinated. U.S. officials and researchers look to the Southern Hemisphere to inform their flu season predictions, and this southern summer, Australia's severe flu season made headlines when the flu vaccine appeared to be mismatched to dominant strains, and effective in only 10 percent of cases.
That statistic may be driving the rising number of people in the Northern Hemisphere questioning the value of the vaccine this season. “We were concerned that the Australia publicity would discourage folks from getting vaccinated," says Schaffner, a fear that appears to have some merit. Indeed, athenahealth network data reveal that since October 2017, vaccination rates have been slightly lower than in the previous two years.
Compounding concerns, vaccination rates in general tend to fall off after Thanksgiving, says Schaffner, despite the benefits to being vaccinated well into January. So, it's likely most people who were going to get vaccinated for the season have already done so.
To spread the word that it isn't too late to for flu protection, Schaffner and other researchers have emphasized in news reports recently that it's not completely accurate to compare Australia to the United States. Significantly fewer people get the annual flu shot in Australia, so the flu can spread more intensely there since the community is less protected.
Separately, Schaffner says, in the U.S., last year's flu vaccine was 30 percent effective against H3N2, “so we shouldn't jump the gun." Researchers do not yet know how effective this year’s vaccine is against H3N2, which, as of the last week in 2017, comprised 87 percent of total influenza cases in the U.S., according to the CDC.
That said, “people forget that our vaccine is multi-compartmental and protects against multiple strains, so it may work well against other [strains] that are still affecting people this flu season," Schaffner says. “There's also been well-documented partial protection [against H3N2] from the flu vaccine. So don't throw the baby out with the bathwater. It's still a good vaccine that prevents hospitalizations and deaths each year."
In sum, physicians should still be encouraging their patients to “run, do not walk, to get your flu shot if you haven't this year," says Schaffner.
Chelsea Rice is a contributor to athenaInsight. Follow her @ChelseaRice.