This season’s flu vaccine was particularly well-suited for children, the U.S. Centers for Disease Control and Prevention said, preventing many of the most severe infections.
The shot overall prevented about 45% of infections during the current flu outbreak, the CDC said in a report. The 2019-2020 flu season started earlier than normal and appears to be lingering longer, after a second strain of the virus began circulating late in the season.
“For the influenza B that started off strong this season, and is severe in kids, the vaccine is working against that strain even though it’s different from what’s in the vaccine,” said Brendan Flannery, the CDC’s lead investigator for the Flu VE Network. “We are still referring to the vaccine as a good match, but we point out that for some people the vaccine doesn’t protect well.”
The effectiveness of the influenza vaccine is often hit-or-miss, since public-health experts design it each year based on projections about which strains will emerge and how they may have mutated from the previous season.
An interim report from the CDC suggests the effectiveness of this year’s immunization falls somewhere in the middle of the 40% to 60% protection normally seen when the vaccine matches up well against the circulating strains.
This season’s outbreak has been marked by a unusually high level of doctor’s office visits for influenza-like illness, accompanied by an unexpectedly low rate of deaths. That may be because the predominant early strain circulating in the U.S was influenza B, which seems to hit children the hardest, while the elderly are most likely to die during a normal flu season.
High rates of the flu have alsoraised concerns that the virus will be mistaken for, or mask cases of, the new coronavirus that has infected tens of thousands in China but largely spared the U.S. The CDC has set up surveys in several large U.S. cities to test for the new virus.
Success in Kids
The vaccine worked well in children, the CDC said, preventing 55% of acute respiratory illnesses that landed kids in the doctor’s office between Oct. 23, 2019 and Jan. 25, 2020, according to the CDC’s Morbidity and Mortality Weekly Report. For everyone, the vaccine cut infections caused by influenza B by half and reduced cases of influenza A, which picked up steam at the end of 2019, by about one-third.
Researchers use a survey of doctor-office visits to estimate the vaccine’s effectiveness. The analysis looked at 4,112 patients who showed up at their doctor’s offices complaining of cold and flu-like symptoms. The majority of those who tested negative for the flu had gotten the vaccine.
Flu levels are still elevated across the country and severe illnesses, including hospitalization rates for children and teenagers, are higher at this point than any recent years, including the 2017-2018 season that left hospitals scrambling, the agency said. Already, 92 children have died from the flu, the highest number for this time point since reporting began in 2004, other than the 2009 swine flu pandemic.
The CDC estimates that at least 26 million Americans have contracted the flu, 250,000 were hospitalized, and 14,000 died.
“CDC recommends that health care providers continue to administer influenza vaccine to persons aged 6 months or greater because influenza activity is ongoing, and the vaccine can still prevent illness, hospitalization, and death associated with currently circulating influenza viruses as well as other influenza viruses that might circulate later in the season,” the agency’s report said.
The news wasn’t all positive. The vaccine isn’t significantly protecting adults up to age 49 against the influenza A strain that began circulating at the end of the year, the agency said.
“The bad news is that not everyone is protected,” said Flannery. “Some people who get the vaccine still get ill.”
Even when the vaccine isn’t well matched, it can offer some protection against illness and even death, the CDC said. Last season, the vaccine was about 29% effective against the circulating strains of the flu. Still, it prevented about 4.4 million illnesses, 2.3 million medical visits, 58,000 hospitalizations and 3,500 deaths, the agency said.
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