How Effective Is the Flu Shot? What Doctors Are Saying About This Year’s Vaccines

Though not perfect, the shots generally provide decent protection.

To begin with the less favorable aspect: Achieving complete effectiveness in vaccines remains a challenge, even though certain vaccines like those for polio and measles exhibit remarkable efficacy. Even vaccines targeted at stable pathogens aren’t infallible due to the varying responses within individuals based on factors such as age and immune system health.

Now, shifting our focus to the influenza vaccine: The efficacy of the flu vaccine fluctuates yearly, as reported by the CDC. Encouragingly, recent research indicates that the vaccine can mitigate the likelihood of illness by approximately 40% to 60% during seasons when it aligns well with the prevalent flu virus strains. The upcoming flu season may present unique complexities, partly attributed to the minimal occurrence of the flu during the previous year.

The reduced prevalence of the flu last year can be attributed to the concurrent measures taken to curb COVID-19 transmission, as elaborated by Dr. Michael Knight, a primary care specialist and assistant professor of medicine at George Washington University Medical Faculty Associates in Washington, DC. These preventive actions encompassed mask-wearing, physical distancing, and regular hand hygiene.

As we approach the upcoming season, a distinctive circumstance arises. The majority of the population has been distanced from exposure to flu viruses for over a year, contributing to a diminished prevalence of natural immunity, as articulated by Dr. Knight. This adjustment introduces a new dynamic in the equation of immunity.

Why isn’t the flu shot 100% effective?

The annual redesign of the flu vaccine is a necessary procedure, as elucidated by the CDC. The flu virus manifests in various strains each year, necessitating the reformulation of the vaccine to effectively combat these evolving strains. Thus, the vaccine’s efficacy experiences fluctuations from year to year, largely contingent on the precision of predicting the dominant strains of the virus.

Dr. William Schaffner, a respected authority in the field, elucidates the dynamic nature of the flu virus. He clarifies that the virus can undergo mutations, resulting in the coexistence of multiple strains, although one usually emerges as dominant. Crafting a vaccine that guards against several strains becomes the annual strategy. Dr. Schaffner further explains the continuous global surveillance of influenza, spanning the entire year, to identify the strains that are likely to have the greatest impact on the upcoming US winter season.

Dr. Schaffner points out, “While we experience flu-free summers, countries below the equator in the southern hemisphere undergo their winter and consequently their flu season. During this period, experts meticulously observe the various strains, striving to forecast which strains will predominate during our winter.”

This year, all flu vaccine manufacturers are producing quadrivalent vaccines, safeguarding against four distinct strains of the influenza virus, as affirmed by the US Food and Drug Administration.

What else affects flu shot effectiveness?

Several additional variables contribute to the annual variability in the effectiveness of the flu vaccine.

Type of vaccine

Researchers have endeavored to ascertain whether the nasal mist vaccine surpasses the injected variant—or vice versa. Diverse studies have demonstrated the nasal spray’s superiority in certain instances, while injections have shown advantages in others, contingent on the recipients’ age and health status. Nonetheless, as a general observation, Dr. Schaffner asserts, “The efficacy of nasal vaccines and injections tends to be comparable.”

Furthermore, this year’s vaccine offerings maintain a uniform focus, comprising quadrivalent formulations that address the same four strains of the flu virus. This approach ensures that if the projections concerning the circulating viruses prove accurate, all administered vaccines will confer a substantial level of protection. The CDC emphasizes the significant benefits: flu shots play a pivotal role in averting illness and potential complications. However, in the scenario of an inaccurate prediction, the efficacy of all vaccine types would be diminished, regardless of the kind received by an individual.

A person’s age

Due to the waning immune response associated with advancing age, the effectiveness of the standard flu vaccine may diminish in older adults compared to younger individuals. To address this challenge, there are two specially formulated flu vaccines designed to elicit a more robust immune response in seniors:

1. High-dose flu vaccine: This vaccine incorporates four times the quantity of antigen—the component of the virus that triggers the immune response—compared to the regular flu shot.

2. Adjuvanted flu vaccine: Similar to the conventional flu vaccine, this variant includes an “adjuvant,” an additive aimed at stimulating a heightened immune response.

Dr. Schaffner affirms, “Both of these vaccines have demonstrated improved efficacy among individuals aged 65 or older.”

Why should you get an annual flu shot, even if it’s not 100% effective?

Ongoing endeavors to enhance the flu vaccine persist. Prominent companies, like Pfizer, are exploring the utilization of groundbreaking mRNA technology akin to that employed in certain COVID vaccines. Notably, there are initiatives underway to combine influenza vaccines with COVID boosters, exemplified by Moderna’s ongoing development. Furthermore, the pursuit of a “universal” flu vaccine capable of combating all influenza strains represents a notable aspiration, as highlighted by the National Institutes of Health.

While the quest for a universal flu vaccine that renders yearly predictions obsolete is ongoing, the existing flu vaccines offer our best line of defense against the disease. Dr. Schaffner emphasizes, “We must acknowledge that the flu vaccine is commendable but not infallible. It exhibits a substantial level of effectiveness. While some individuals may contract the flu despite being vaccinated, the severity of their infection is markedly reduced. Their likelihood of hospitalization and mortality is significantly diminished.”

As per the CDC, flu vaccines prevent millions of illnesses and medical consultations annually. In the pre-pandemic 2019-2020 flu season, the flu vaccination was estimated to prevent around 7.5 million influenza cases, 3.7 million influenza-related medical visits, 105,000 influenza-associated hospitalizations, and 6,300 influenza-associated fatalities.

The efficacy of this year’s flu shot remains uncertain. However, it is worth noting that only approximately half of Americans choose to receive the flu vaccine annually, based on CDC data. It is crucial to emphasize that the vaccine’s effectiveness is contingent upon its administration.