Flu Shots: Are They ‘Live Virus’ Vaccines or Not?

The answer depends on the type of flu shot you receive.

In the United States, the annual resurgence of the flu is a familiar occurrence. If you’re hesitating to receive your yearly flu shot due to concerns about contracting the flu from the vaccine, rest assured, such an outcome is implausible.

Dr. Michael Knight, a primary care physician and assistant professor of medicine at George Washington University Medical Faculty Associates in Washington, DC, sheds light on the misconceptions surrounding the flu vaccine. He notes, “The reputation of the flu vaccine has occasionally been marred by anecdotes like, ‘My acquaintance received the flu vaccine and subsequently fell ill with the flu the very next day.’ However, it’s crucial to understand that the flu vaccines in use are incapable of inducing the flu virus.”

This misconception might stem from the diverse methods employed in the development of these vaccines. To provide clarity on flu vaccines, including their variants and production processes, Health Magazine engaged experts to share insights.

What Types of Vaccines Are There?

The U.S. Department of Health & Human Services (HHS) categorizes vaccines into several general types:

1. Live, Attenuated: These vaccines contain a live but weakened form of a virus or bacteria.

2. Inactivated: These vaccines consist of an inactivated version of a virus or bacteria.

3. Toxoid: This type includes weakened toxins that might cause an illness.

4. Subunit, Recombinant, Polysaccharide, and Conjugate: These vaccines utilize components of the virus or bacteria rather than the entire organism.

5. Messenger RNA (mRNA): This type prompts the production of proteins designed to initiate an immune response against a virus.

6. Viral Vector: These vaccines employ a modified version of a different virus (acting as a vector) to confer protection against a specific virus.

In particular, live, attenuated vaccines feature a live yet attenuated (weakened) version of a virus or bacteria, while inactivated vaccines contain a virus or bacteria that has been rendered non-functional. Dr. Knight elucidates this historical progression: “During the initial phases of flu vaccination, live attenuated virus vaccines were utilized. However, this posed challenges for individuals with compromised immune systems or pregnant patients.”

Subsequently, advancements led to the use of inactivated viruses in flu vaccines, eliminating the risk of illness following vaccination. Although most flu vaccines today contain inactivated viruses, an exception exists: one flu vaccine, as outlined by the Centers for Disease Control and Prevention (CDC), still employs a live attenuated virus.

How Are Flu Vaccines Made?

1. Inactivated Vaccines

The process employed to produce the majority of flu vaccines, utilizing an egg-based approach, was originally pioneered over 80 years ago, as outlined by the CDC. The process commences with either the CDC or another laboratory within the World Health Organization’s Global Influenza Surveillance and Response System. These entities responsible for public health supply private manufacturers with the selected viruses for the vaccine of the particular season. Following this, these viruses are cultivated within eggs in adherence to stringent regulations set by the US Food and Drug Administration.

Dr. William Schaffner, the medical director of the National Foundation for Infectious Diseases and a professor of preventive medicine and infectious diseases at Vanderbilt University School of Medicine, elucidated the historical context, stating, “The technology emerged during the late 1930s and 1940s, when scientists initially realized that influenza viruses could be cultured within chicken eggs.”

This intricate technological process involves using exceptionally pure eggs, bred on specialized farms that protect them from potential contamination by wild birds. Dr. Schaffner emphasized, “Given that we need to produce a vast quantity of vaccine doses, the demand for eggs is substantial.”

Regardless of the method employed for virus growth, the viruses are cultivated in significant quantities before being extracted from the eggs or cells. “The virus is then rendered inactive and broken down into fragments,” Dr. Schaffner explained. “These essential viral components responsible for stimulating an immune response are isolated, purified, and serve as the basis for the vaccine.” Dr. Schaffner emphasized that it is impossible to reconstruct the virus from these components, underscoring the impossibility of contracting the flu from the vaccine.

Specific versions of the flu vaccine cater to individuals aged 65 and above. These versions incorporate the same inactivated virus as the standard dosage vaccine. One of these formulations, designed for seniors, is high-dose, containing four times the quantity of the inactivated virus found in the regular shot. An alternate version contains the same antigen concentration but also includes an adjuvant, a substance that enhances the immune system’s response.

In addition to traditional egg-based methods, a more contemporary technique of vaccine production involves cultivating viruses in animal cells within large laboratory vessels, as highlighted by the CDC.

2. Live, Attenuated Flu Vaccines

One category of flu vaccine does indeed incorporate a live but attenuated (weakened) virus. This formulation takes the form of a nasal mist and is designated for individuals aged 2 to 49 who are not pregnant and do not have any significant underlying health conditions, in accordance with CDC guidelines.

In the case of this particular vaccine, the CDC outlines the initial steps that mirror the egg-based growth process utilized for injections. However, instead of inactivating the viruses, they undergo an alternative production procedure that renders them weakened. According to the CDC, “These attenuated viruses possess cold-adapted traits, meaning they are engineered to solely replicate in the cooler nasal temperatures, avoiding replication in the lungs or other regions with higher temperatures.”

Dr. Schaffner enthusiastically describes this innovative process as “a marvel of contemporary scientific achievement.” Through meticulous molecular engineering, the viruses are manipulated to function exclusively within the cooler nasal environment. “The viruses’ inability to replicate at the slightly elevated temperature present in the lungs, as compared to the nasal area, is a result of this intricate engineering. This renders the viruses completely inept at generating influenza,” adds Dr. Schaffner.

What Else To Know About Flu Vaccines

During a given flu season, the array of available flu vaccines collectively guard against the four viruses identified as the most probable sources of concern for that particular season. Notably, the period required for the development of protective antibodies against influenza viruses spans approximately two weeks. As such, the optimal timeframe for vaccination, as suggested by the CDC, is by the conclusion of October. Nevertheless, if circumstances warrant, individuals might be eligible to receive their vaccination as early as July or August.

It is advisable for individuals aged six months and older to receive vaccination, excepting certain demographics such as children below the age of six months, in accordance with CDC recommendations. Moreover, individuals with allergies to eggs can indeed receive flu vaccinations. However, as of August 2022, two egg-free flu vaccines are available. It is pertinent to note that individuals with severe egg allergies, which entail reactions beyond just hives, should undergo vaccination under the supervision of a healthcare professional, as advised by the CDC.

A Quick Review

Several distinct varieties of flu vaccines are accessible for safeguarding against the virus every flu season. Should any lingering uncertainties persist regarding receiving the flu vaccine, it is recommended to engage in a conversation with your healthcare provider. They can offer comprehensive information and personalized guidance to address your concerns effectively.