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  • Cases of flu are rising rapidly, particularly in southern and eastern states.
  • October saw 1.6 million people in the US with symptoms of the virus.
  • Reasons for the fast spread include reduced immunity, low vaccination uptake and an end to COVID-19 mitigation measures.
  • The flu shot continues to provide the best protection against the virus.

This year’s flu season is already showing signs that we could see an extremely high number of cases.

The Centers for Disease Control and Prevention (CDC) estimated that — in October alone — at least 1.6 million individuals in the US had the flu, while a minimum 13,000 cases resulted in hospital admissions. A total of 730 deaths were also recorded, Two of which were children.

We’re still months away from the estimated peak of flu season, which usually occurs in February and March. This has led the CDC to state that this flu season will likely be the worst in 13 years. So what’s going on?

According to experts, three primary factors have been driving the rapid rise in cases.

Even as we move away from the height of the COVID-19 pandemic, its effects continue to make themselves known.

COVID-19 restrictions, such as mask-wearing and social distancing, significantly reduced viral transmission.

The result?

“Unprecedentedly mild flu seasons(s) in 2020-2021,” stated Dr. Jason Kessler, section chief of the Infectious Disease Department of Medicine at Morristown Medical Center, part of Atlantic Health System.

Kessler told Healthline, “annual exposure [to viruses] helps ‘prime’ our immune systems to either prevent or attenuate these infections each year.”

COVID-19 measures prevented exposure, and “this likely had the unintended effect of increasing many individuals’ susceptibility to infection and illness,” he added.

With COVID-19 mitigation measures lifted, the seasonal flu is once again spreading.

Additionally, with few flu cases during the pandemic, “the virus has had a long time to mutate,” Dr. Shruti Gohil, associate medical director of epidemiology and infection prevention at UCI Health. said. And, in the face of our lower immunity, this allowed it to hit harder.

Two flu vaccine-related factors could be playing a role in the spike in cases.

The first is the number of people getting vaccinated (or not). Kessler highlighted that “the pandemic has been associated with a general increase in concerns about vaccine hesitancy and resistance.”

He noted that, while not proven as of yet, this may lead to reduced numbers of people getting their flu shot. And, “if influenza vaccination has not penetrated widely in the community, more intense influenza spread could result.”

“Vaccine rates against influenza dipped in the 2020-2021 season compared to the prior year,” said Gohil.

Another factor is that the flu shot isn’t 100% effective against the disease. It is developed each year according to what researchers believe will be the most prevalent strains for flu season. Sometimes strains change or mutate by the time flu season hits, making the vaccine less effective.

In general, the flu vaccine has been about 30 to 60 percent effective at preventing the flu in recent years, according to the Centers for Disease Control and Prevention.

But that doesn’t mean you should avoid getting vaccinated.

“Some protection is better than none, and we’re talking about a possibly fatal virus,” explained Dr. Cesar A. Arias, co-director of the Center for Infectious Diseases Research at the Houston Methodist Research Institute.

“Flu kills about 35,000 people each year in the US,” he told Healthline. “The whole idea [of vaccination] is to try to protect you from this. Ask anybody if they want to avoid death, and I think the answer would be a resounding yes!”

Another reason flu cases appear high, other diseases including respiratory syncytial virus (RSV) are spreading widely and may be mistaken for the flu.

“It is important to recognize that what is generally referred to as ‘flu’ may not always be caused by the influenza virus,” revealed Kessler.

Instead, he continued, they “can be related to infection with several different viruses: influenza virus, respiratory syncytial virus (RSV), parainfluenza virus, and SARS-CoV-2 (the virus that causes COVID-19), as well as others.”

These viruses spread among the population in the same way and have many of the same symptoms — such as fever, runny nose, coughing, and fatigue.

Unless a test is performed, it can be hard to distinguish between them.

A general increase in other viruses, such as RSV, is also likely due to the lifting of post-pandemic restrictions, added Arias, as we engage in closer contact with others while having reduced immunity.

CDC data shows that flu cases are currently high among populations in eastern states, such as New York, Virginia, and North Carolina.

This is not unsurprising, revealed Gohil, as “in general, influenza infection usually moves east to west.”

Arias explained this might be because the East Coast is faced with colder weather first, and viruses thrive in colder temperatures.

However, southern states — such as Florida, Mississippi, Alabama, and Georgia — are also being hit hard by the flu.

“I think a factor in these states is that there are much lower vaccination rates than you see in other parts of the US,” said Arias.

Historically, these areas are shown to have up to 50% less uptake of flu shots compared to northern states such as Maine, New Hampshire, and Washington.

“Flu-like illnesses and flu test positivity rates are higher this year compared to similar time periods in prior years,” stated Gohil.

However, it’s not just the US seeing the earlier wave of infections. “Influenza hit 2 months earlier in Australia,” Gohil said, while Chile also experienced the same pattern.

The number of hospitalized individuals is also notably elevated compared to this time in previous years. The CDC reported that ‘the cumulative hospitalization rate…is higher than the rate observed in week 43 during every previous season since 2010-2011.’

That said, it is the same population being admitted to hospital. “As with previous years, hospitalizations have been highest in the elderly (65 years or older) and the very young (4 years old and under),” Gohil shared.

“For children, a less well-developed immune system is likely the reason for this,” she continued. Meanwhile, “elderly patients have a weakened immune system associated with aging.”

Flu cases and associated hospitalizations are rising rapidly. The three key reasons behind this are believed to be:

  • Reduced immunity and germ exposure following pandemic restrictions
  • Low vaccination uptake and potentially reduced vaccine efficacy
  • The concurrent spread of other respiratory viruses with similar symptoms

Children, older individuals, and those with compromised immune systems are at the greatest risk of serious flu symptoms. However, Arias noted, “even if you’re completely healthy, certain individuals will [still] have severe disease.”

The best protection against the flu is vaccination. But wearing a mask — especially in crowded indoor spaces — can also offer a level of defense. Particularly if you’re a higher-risk individual, “a mask may save your life,” stated Arias.