Younger- and middle-age adults took a particularly hard hit from the flu season, according to the Centers for Disease Control and Prevention’sMorbidity and Mortality Weekly Report (MMWR ).
People age 18-64 represented 61 percent of all hospitalizations from influenza compared with the previous three seasons when this age group represented only about 35% of all such hospitalizations. Flu deaths followed the same pattern with more deaths than usual occurring in this younger age group.
A second MMWR report showed that influenza vaccination offered substantial protection this season, reducing a vaccinated person’s risk of having to go to the doctor for flu illness by about 60% across all ages.
“Flu hospitalizations and deaths in people younger- and middle-aged adults is a sad and difficult reminder that flu can be serious for anyone, not just the very young and old; and that everyone should be vaccinated,” said CDC Director Tom Frieden, M.D., M.P.H. “The good news is that this season's vaccine is doing its job, protecting people across all age groups."
Ain't over til it's over
U.S. flu surveillance data suggest flu activity is likely to continue for several weeks, especially in places where activity started later in the season. Some states that saw earlier increases in flu are now seeing decreases. Other states are still seeing high levels of flu activity or continued increases.
While flu is responsible for serious illness and death every season, the people who are most affected can vary by season and by the predominant influenza virus. The currently circulating H1N1 virus triggered a pandemic in 2009, in which there were high rates of hospitalization and death in younger- and middle-aged people. While H1N1 viruses have continued to circulate since the pandemic, this is the first season since then that they have been predominant in the U.S. Once again, the virus is causing severe illness in younger- and middle-aged people.
High hospitalization rates
Approximately 61% of flu hospitalizations so far this season have occurred among persons aged 18-64 years. Last season, when influenza A (H3N2) viruses were the predominant circulating viruses, people 18 to 64 years accounted for only 35% of hospitalizations. During the pandemic season of 2009-2010, people 18 to 64 years old accounted for about 56% of hospitalizations.
Hospitalization rates have also been affected. While rates are still highest among people 65 and older (50.9 per 100,000), people 50 to 64 years now have the second-highest hospitalization rate (38.7 per 100,000), followed by children 0-4 years old (35.9 per 100,000). During the pandemic, people 50 to 64 years also had the second-highest hospitalization rate. Note that hospitalization rates are cumulative and thus will continue to increase this season.
Flu deaths this season are following a pattern a similar to the pandemic. People 25 years to 64 years of age have accounted for about 60% of flu deaths this season compared with 18%, 30%, and 47% for the three previous seasons, respectively. During 2009-2010, people 25 years to 64 years accounted for an estimated 63% of deaths.
"Younger people may feel that influenza is not a threat to them, but this season underscores that flu can be a serious disease for anyone," said Dr. Frieden. "It's important that everyone get vaccinated. It's also important to remember that some people who get vaccinated may still get sick, and we need to use our second line of defense against flu: antiviral drugs to treat flu illness. People at high risk of complications should seek treatment if they get a flu-like illness. Their doctors may prescribe antiviral drugs if it looks like they have influenza."
People at high risk for flu complications include pregnant women, people with asthma, diabetes or heart disease, people who are morbidly obese and people older than 65 or children younger than 5 years, but especially those younger than 2 years.
The value of flu shots
In the flu vaccine effectiveness (VE) study, CDC looked at data from 2,319 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness (Flu VE) Network from December 2, 2013, to January 23, 2014. They found that flu vaccine reduced the risk of having to go to the doctor for flu illness by an estimated 61% across all ages. The study also looked at VE by age group and found that the vaccine provided similar levels of protection against influenza infection across all ages.
VE point estimates against influenza A and B viruses by age group ranged from 52% for people 65 and older to 67% for children 6 months to 17 years. Protection against the predominant H1N1 virus was even slightly better for older people; VE against H1N1 was estimated to be 56% in people 65 and older and 62% in people 50 to 64 years of age. All findings were statistically significant.
The interim VE estimates this season are comparable to results from studies during other seasons when the viruses in the vaccine have been well-matched with circulating influenza viruses and are similar to interim estimates from Canada for 2013-14 published recently.
While flu vaccine can vary in how well it works, vaccination offers the best protection currently available against influenza infection. CDC recommends that everyone 6 months and older get an annual flu vaccine.
“We are committed to the development of better flu vaccines, but existing flu vaccines are the best preventive tool available now,” said Dr. Frieden. “This season vaccinated people were substantially better off than people who did not get vaccinated. The season is still ongoing. If you haven’t yet, you should still get vaccinated."
Younger- and middle-age adults took a particularly hard hit from the flu season, according to the Centers for Disease Control and Prevention’s Morbidity an...