How Effective Is Getting A Flu Shot?

Influenza, an acute, highly contagious respiratory disease caused by a variety of different viruses, has been a thorn in humanity’s side for millennia.

Records of an upper respiratory illness with symptoms consistent with influenza date as far back as 412 BC with Hippocrates’ writings of the “cough of Perinthus”. For most of the time since, society has been ill-equipped to deal with the disease in any meaningful way. That is, until 1936 when the first antibodies for influenza were isolated, which would later provide the foundation for subsequent vaccines against influenza.

Luckily, in the current era, we have access to the fruits of modern medicine, and with them the flu vaccine. Despite this, you may have heard that the flu shot is not 100% effective. To understand why this is, it’s helpful to first have an understanding of how the flu vaccine is created.

How the flu vaccine is created

In common parlance, “seasonal flu” is something with which we are all too familiar. How the flu vaccine is created, on the other hand, is less well known.

The process of creating an effective vaccine against seasonal flu is a complicated, ongoing one. Influenza is subject to something called antigenic drift: mutations within the genes of the virus that cause changes to the structures to which the immune system responds. These structures, called antigens, are what the immune system recognizes after it has had exposure to the virus. This recognition will trigger the production of antibodies which block infection. Antigenic drift happens continually as the virus replicates over time.

Vaccines, including the influenza vaccine, generally involve exposure to an innocuous form of the disease to enable antibody production within the patient, thereby preempting the body’s immune response system before true exposure.

Antigenic drift becomes a problem when the mutated form of the virus changes such that it no longer resembles the disease against which a patient was inoculated. The body’s immune system is no longer able to recognize the virus and prevent infection.

The antibodies created by the vaccine no longer recognize the mutated form of the virus.

Why do you need to get the flu shot every year?

The Center for Disease Control is tasked with predicting the degree to which influenza will antigenically drift between flu seasons. This is why it is recommended that one get their flu shot annually as opposed to other vaccines which are taken far less frequently.

This is also why a flu shot is not a 100 percent guarantee that one will not contract flu: sometimes the degree to which a virus has drifted is such that the flu vaccine does not guarantee immunity.

Because there is so much variance to the influenza virus, largely in part to antigenic drift, the CDC must closely monitor just how effective vaccines are. They utilize several different networks to monitor persons hospitalized with respiratory illness. Upon testing for influenza, the frequency of influenza vaccination among patients is observed compared to non-vaccinated patients.

How effective were flu shots in the past?

Every year, the CDC plays this game of cat and mouse with influenza where they are charged with predicting the genetic makeup of the viruses that will comprise the seasonal flu. During the 2019-2020 flu season, for example, the flu shot was 29% effective. In the previous season, that number was closer to 38%. In the 2015-2016 season, the flu shot was 48% effective. [Source]

flu shot data

Some years are more successful than others.

How effective will the flu shot be in 2020/2021?

It is, of course, not known what that number will look like for the flu season we currently find ourselves in as the extent of antigenic drift can vary greatly and data will not be available until after the season ends.

Yet even viruses that have antigenically drifted greatly still share genetic similarities with their original form. As a result, there is still a protective benefit from the flu vaccination. Even in the worst case scenario of infection despite having been vaccinated, this partial immunity might mean less severe symptoms and/or a shorter duration of infection.

Ultimately, the flu shot is effective and is strongly recommended, especially during a pandemic when hospitals might be over-burdened with COVID-19 cases and have a more difficult time supporting seasonal flu cases.

How long does a flu shot last?

The flu shot is seasonal for a reason: as we have discussed, influenza possesses certain properties which make it difficult to vaccinate against in perpetuity. So when we ask for how long a flu shot will last, the true answer is variable depending on the genetic makeup of the flu which appears annually.

In general, though, the flu shot will protect for 4 – 6 months after your vaccination. Getting a flu shot every year in September – October will ensure that you are as prepared as possible for the duration of flu season.

Are flu shots effective for people over 50 and seniors?

It is recommended that seniors get their annual flu vaccination. Analysis of the effectiveness of flu vaccine among seniors aged 60 and over indicate efficacy percentages at 52% in years when the seasonal flu strain was well predicted; effectiveness was closer to 36% when the vaccine was not well matched to the ultimately predominant flu strain.

Are flu shots effective for toddlers and young children?

The CDC also recommends that children be vaccinated. In a four year study which analyzed the efficacy of the flu vaccine among children aged 1 to 15, rates of successful vaccination were 77% and higher for a particular, common strain of the seasonal flu.

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At-Home Flu Shots With Concierge MD

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