After circulating at near-zero levels last year, influenza is on the rise in most of the United States.
That’s according to the US Centers for Disease Control and Prevention. latest flu reportpublished Friday, which also notes that the number of flu-related hospital admissions has increased every week for the past seven weeks.
“I have been tracking recent flu activity nationally and locally. We are not surprised that influenza activity is increasing,” said Dr. Angela Branche, an infectious disease specialist and associate professor of medicine at the University of Rochesterhe wrote in an email on Wednesday.
“I’m a bit surprised that it’s still mostly H3N2 infections and not influenza B. I might have expected a wave of influenza B this late in the flu season,” Branche wrote.
Influenza A and B viruses cause most illness in the United States, especially during the flu season. The influenza A subtypes are H1N1 and H3N2. Influenza A H3N2 viruses have been the most frequently detected influenza viruses this season, according to the CDC.
“In a year without a pandemic, this pattern of flu activity would not be entirely unusual; see a spike in influenza cases in January and then decline with another spike in early spring,” added Branche.
The CDC estimates that so far this season, there have been at least 3.1 million flu cases, 31,000 hospitalizations and 1,800 flu deaths, as of Friday.
By comparison, the lower end of CDC Flu Estimates for each year between 2010 and 2020 it included 9 million cases, 140,000 hospitalizations and 12,000 deaths.
While flu activity has increased in most parts of the country, the highest levels have been in the central and south-central regions of the United States, according to the CDC.
Some schools in these areas have canceled classes due to an increase in the flu.
Johnson County Schools in Tennessee closed March 11, citing an “excessive number” of influenza cases. The closure gave custodians time to thoroughly clean buildings before schools reopen next week.
“We closed one day due to increased staffing due to the flu and not having enough substitutes to cover,” Johnson County Schools Director Mischelle Simcox wrote in an email Tuesday.
“We did this on a Friday which gave us a long weekend to help staff members recover and feel better,” Simcox wrote. “We haven’t had to close for the flu since 2020. We only close when we have a large number of employees out and we don’t have enough coverage for our staff. During this time, our custodians are taking additional steps to sanitize and clean all areas of the buildings.”
In the west, Oregon health official Dr. Dean Sidelinger said the spike in flu cases there could be an indication of a surge. About 3.1% of reported tests in Oregon came back positive for the flu in the week ending March 12, he said, compared with 2.5% the week before.
Nationwide, for the week ending March 19, 7.7% of specimens tested in clinical laboratories for the influenza virus were reported to the CDC as positive for influenza.
“We are concerned because this is usually the time that our flu season is ending, but we are seeing this increase in cases and it could be related to people’s behavior – removing their masks and going back to some of their more normal activities. Sidelinger said Tuesday.
He added that current flu levels are still “well below” what has been reported in Oregon for pre-pandemic flu seasons. In March 2019the percentage of influenza tests that were positive was nearly 40%.
“Like the rest of the country, we saw very little flu last year,” Sidelinger said. “That was not because the flu virus disappeared. But those measures that people took to combat Covid-19 — wearing their masks, limiting their gathering, trying to move things outside where the spread of respiratory viruses is harder and less easy — certainly limited the flu.”
Branche also cited the rollback of Covid-19 mitigation measures as having a role in the increased flu activity.
“Because H3N2 has remained in circulation for the past several months, even at low levels, I believe the current increase in H3N2 cases is likely more related to the relaxation of COVID19 mitigation strategies, such as the use of face masks. and social distancing,” he said. he wrote.
viral competition – which describes when respiratory viruses can compete for people to infect – may also play a role.
This concept “has been theorized for many years, and intuitively makes sense when it comes to adults, as they are much less likely to be co-infected and are typically only infected with one virus at a time,” Branche wrote. . “So that’s a possible explanation.”
Influenza is contributing to levels of respiratory illness in the United States, but the CDC notes that other respiratory viruses are also circulating.
The CDC also notes that while the number of flu-related hospital admissions reported to the US Department of Health and Human Services has increased weekly for the seventh week in a row, the cumulative hospitalization rate for this flu season is more higher than the rate for the entire 2020-2021 season, but still lower than the rate seen at this time during the four flu seasons that preceded the Covid-19 pandemic.
Influenza activity decreased from mid-December through January, According to the Centers for Disease Control and Prevention. At that time, Covid-19 cases were on the rise. Then, when flu cases started to rise earlier this year, Covid-19 cases went down.
As coronavirus mitigation measures like mask wearing and social distancing roll back in states across the country, why has the nation seen an increase in the flu but not Covid-19?
“I think the reason we’re not seeing covid cases going up right now is a combination of high vaccination rates, with a lot of people in Oregon being up to date on their covid shots, and then people who have been recently recovered during this larger surge, this Omicron surge, and they still have a level of protection,” Sidelinger said.
“So we’re in a place where we have fewer people susceptible to the disease right now than we have at earlier times in the pandemic,” he said. “This is why we continue to see the numbers go down even when the masks are removed.”
The National Association of City and County Health Officials hasn’t heard much from its members about the rise in flu cases, but the national rise in cases could be related to fewer people getting flu shots this year and this season’s flu vaccine may not be as effective as previous seasons, Lori Tremmel Freeman, executive director of NACCHO, said Wednesday.
However, “even if it’s less effective than usual, it still has the ability to provide some protection that might lessen the symptoms or duration of the flu,” Freeman said. “So I wouldn’t necessarily give up the flu shot, because it can still be helpful in preventing more serious illness.”
This flu season, based on data from 3,636 children and adults who got the flu between October and mid-February, the vaccine did not appear to reduce the risk of getting sick from influenza A (H3N2) viruses that have been predominant, according to CDC Morbidity and Mortality Weekly Report published this month. The overall effectiveness of the vaccine against infection was 16%, which is not considered statistically significant.
However, there were not enough enrollments in that study to reliably understand how effective it was, and the CDC is studying how well the current vaccine protects against serious illness.
In general, the flu vaccine is known to reduce the risk of hospitalization or death from the flu, and the CDC still recommends that people get a flu shot, even late in the season. the CDC Dear that during the 2019-2020 season, influenza vaccination prevented approximately 105,000 influenza-related hospitalizations.
“Americans should always be encouraged to get vaccinated against influenza. Influenza has always been a health threat to vulnerable members of our communities and that remains the case, even during the pandemic,” Branche wrote in his email.
“I usually don’t strongly recommend my patients get a flu shot this late in the season, but with the rise in cases and the uncertainty of how things will play out in the coming months, it’s still worth getting vaccinated if you don’t it has done. so until now for the 2021-2022 season.”