Is It Too Late to Get the Flu Shot and How Effective Is It in 2021-2022?

Public attention may understandably be focused on COVID and the Omicron variant this winter season, but the flu is still circulating.

In November, the University of Michigan reported an outbreak of a flu type known as influenza A or H3N2. It affected at least 745 people within the university between October 6 and November 19, and one person was hospitalized.

Following an investigation into the outbreak, the Centers for Disease Control and Prevention (CDC) stated that it highlighted "the importance of increasing vigilance for influenza disease this winter" especially with COVID already putting stress on healthcare systems.

The health agency noted that one measure to help mitigate influenza severity is the flu vaccine.

Typically, people get a flu vaccine before the flu season actually starts, rather than during it. Flu activity varies but it tends to start increasing in October before peaking some time between December and February.

Yet while we may be well into the flu season at the moment, it is still not too late to get a flu vaccine according to the CDC, which states that "even if you are not able to get vaccinated until November or later, vaccination is still recommended because flu most commonly peaks in February and significant activity can continue into May."

It's thought that flu vaccines prevent millions of illnesses and related visits to the doctor every year, as well as thousands of deaths.

Flu vaccines, like others, do have the potential to cause some short-term side effects. These include soreness from getting the shot, headache, fever, nausea and muscle aches.

The CDC also notes that for every million people vaccinated with a flu shot, fewer than one or two may develop Guillain-Barré syndrome (GBS)—a disorder in which the immune system damages nerves. It can lead to muscle weakness and sometimes paralysis, but most people fully recover.

However, the cause of the link between GBS and the flu vaccine is unknown and the CDC states that the possibility of getting GBS is higher with the flu than with the flu vaccine.

This year, there has been some concern that the current flu vaccines do not match one of the main circulating viruses, H3N2.

The concern was raised in a pre-print study by Scott E. Hensley, a professor in the department of microbiology at the University of Pennsylvania's Perelman School of Medicine, and colleagues. A pre-print means that the study is new and has not yet been through the rigorous peer-review process to verify its findings.

It found that antibodies produced by the 2021-2022 Northern Hemisphere flu vaccine poorly neutralize new H3N2 strain because of new mutations it has.

However, the study also noted that seasonal influenza vaccines "consistently prevent hospitalizations and deaths even in years where there are large antigenic mismatches."

The CDC says it "constantly reviews the composition of flu vaccines and suggests updates when needed to keep up with the latest flu viruses."

Flu vaccine
A stock image shows a person being vaccinated by a health worker. Flu vaccines are updated in order to match mutating flu viruses. ~User7565abab_575/Getty