December 28, 2021—Flu season has started in many parts of the United States. CDC’s most recent FluView report, shows flu activity is highest in the eastern and central parts of the country and lower in the western part of the country. The first two flu-related deaths in children this season were also reported. People 5-24 years account for most cases so far this season; however, the proportion of flu illness in people 25-64 years is increasing. An emerging group of H3N2 viruses is causing most flu activity, so far. CDC recommends flu vaccination as the best protection against flu viruses, including current H3N2 viruses.

Flu Hospitalizations are Rising

To date, 405 hospitalizations have been reported through CDC’s 14-state surveillance system called FluSurvNET. This is already higher than the 232 flu hospitalizations reported last season through that same system.

A new, nationwide surveillance system for hospitalizations called HHS-Protect Hospitalization Surveillance shows 1,265 patients were admitted to hospitals with flu the past week. This is an increase compared to the 1,058 flu hospitalizations reported the previous week.

Vaccination is the Best Protection Against Serious Flu Illness

While some data suggest that vaccine effectiveness against the current predominant H3N2 viruses may be reduced, CDC continues to recommend flu vaccination. CDC has been evaluating human antibody responses to the emerging H3N2 viruses in blood samples collected from people who have been vaccinated as well as from people who have not received this season’s flu vaccine. Compared with unvaccinated people, many vaccinated people had antibodies that neutralized the emerging H3N2 virus. This is consistent with some level of protection against those H3N2 viruses.

Current U.S. flu vaccines are designed to protect against four different flu viruses: A(H1N1), A(H3N2) and two flu B viruses. The flu season is just getting started and while the timing of flu seasons can vary, flu activity most commonly peaks in February and can last into May. Also, during most flu seasons, different flu viruses spread over the course of the season.

Flu vaccination has many benefits yet early data suggest the number of people who have been vaccinated so far this season is down, especially among certain higher risk groups such as pregnant people and children. Lower vaccination rates and reduced population immunity resulting from historic low flu activity since March 2020 could lead to widespread flu, with more serious illnesses. With ongoing COVID-19 activity, hospitals could be further stressed this winter.

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