This past summer, health experts were concerned the United States could experience a "twindemic"—in which both Covid-19 cases and influenza cases skyrocket—in the fall and winter. But CDC data shows that may have been avoided so far, thanks in part to coronavirus countermeasures and high flu vaccination rates.
Flu activity remains low
According to CDC, just 56 people were diagnosed with the flu out of nearly 40,000 tests in the United States during the week ending in Dec. 5, and all 50 states were experiencing either low or minimal activity of influenza-like illnesses. In comparison, at this time last year 23 states were experiencing widespread flu activity. Overall, since Sept. 27, just 429 people have tested positive for influenza.
However, CDC did report that the first pediatric influenza death of the 2021-22 flu season occurred in the week ending in Dec. 5.
According to Kinsa Health, a company that monitors flu trends using thermometers that connect to cell phones, flu numbers are likely to continue to be low. "Going forward, we don't expect influenza-like illness to go high," Inder Singh, founder and CEO of Kinsa, said. "It looks like the twindemic isn't going to happen."
Why flu activity is so low
Experts cited several potential reasons for the unusually mild flu season this year.
1. Coronavirus countermeasures in the US—and abroad
According to experts, novel coronavirus countermeasures, such as mask-wearing and social distancing, depressed influenza transmission rates both in the United States and in the Southern Hemisphere—an area of the world that Daniel Jernigan, director of CDC's influenza division, said has traditionally helped "reseed" influenza viruses that end up in the Northern Hemisphere.
Further, New Zealand and Australia closed off their borders to all noncitizens or Americans, meaning air travel from Southern Hemisphere countries has been minimal—and the transfer of influenza from those Southern Hemisphere countries has been minimal, according to the New York Times.
2. Uptick in flu vaccine production
Moreover, according to Jernigan, a "phenomenal number" of flu vaccines were manufactured and shipped in August—a month earlier than typical. CDC data shows 188 million doses had been shipped as of late November, compared with 175 million last year, and drugmakers estimate that as many as 198 million vaccines will be distributed throughout the United States.
And according to preliminary data, flu vaccination rates at doctor's offices or pharmacies are higher than last year, with about 70 million adults receiving a shot in those locations as of mid-November compared to 58 million last year.
However, Ram Koppaka, CDC's associate director for adult immunization, cautioned that those numbers may be misleading, as it's not clear whether it indicates more people getting vaccinated overall, or merely accounts for people who would have otherwise gotten vaccinated at work. "The best we can say is that it appears that we are now about where we were last year," Koppaka said, adding that "[w]e need to keep telling people that it's not too late to get a flu shot."
In another note of caution, CDC noted that just 54% of pregnant women have received a flu vaccine this year, compared to 58% last year, and just 33% of Black children have received a vaccine this year, compared to 44% last year.
Koppaka said the drop in vaccination rates among Black children was "a point of concern" and something CDC will monitor "over the coming weeks very closely."
He added it's not clear why the vaccination rates among Black children have dropped but emphasized the importance for public health officials to work with communities of color to build a sense of trust in vaccines.
Experts emphasize caution is still important
While flu activity appears to be low now, CDC warned the data should be interpreted with "extreme caution.".
CDC data is based in part on reporting from doctors' offices and hospitals, and because of reporting delays, there's a lag between when flu activity increases in an area and when CDC confirms that increase.
As Lynnette Brammer, head of CDC's domestic influenza surveillance team, put it, flu activity is "at a historical low, but that doesn't mean it's going to stay that way."
Brammer added that once many countries in the Southern Hemisphere eased back on coronavirus countermeasures, influenza rates started to increase. "We do know that when people let up on those measures, flu can come back," she said.
And Jernigan added that while the flu is "atypically low" so far this year, it's not a guarantee for the rest of this flu season. "I don't think we can definitively say there will be no twindemic," he said. "I've been working with flu for a long time, and I've been burned."
And CDC emphasized that getting a flu vaccine is still paramount. "In the context of the ongoing pandemic, flu vaccination is considered more important than ever to help ensure that influenza illnesses and hospitalizations do not further tax an already overburdened health care system," CDC said (Fay Cortez, Bloomberg, 12/11; McNeil, New York Times, 12/13; Castronuovo, The Hill, 12/10; Aldridge, Miami Herald, 12/10; AP/KTLA, 12/9).