Science Fact Check: Was the Definition of COVID Vaccine ‘Changed’?

COVID-19 vaccination has been the subject of immense scrutiny and misinformation since the vaccines were first administered in the U.S. nearly four years ago.
In the first year alone, it is estimated that vaccinations prevented 14.4 million deaths globally, according to estimates by Imperial College London. However, vaccination has not eliminated the disease—a fact that many of its opponents have jumped on.
Across social media, skeptics have claimed that the COVID-19 vaccinations are “ineffective” and do not fit into the historical definition of a vaccine. But what does the science say?
The Claim
There are widespread claims on social media that the U.S. Centers for Disease Control and Prevention (CDC) and the Merriam-Webster Dictionary changed their definition of vaccine in 2021.
On September 8, 2021, U.S. Representative Thomas Massie shared a post on X, (formerly Twitter) showing three different definitions of the word vaccination.
“Check out @CDCgov’s evolving definition of ‘vaccination,'” he wrote. “They’ve been busy at the Ministry of Truth.”
An image below contained the following text:
Vaccination (pre-2015): Injection of a killed or weakened infectious organism in order to prevent the disease.
Vaccination (2015 – 2021): The act of introducing a vaccine into the body to produce immunity to a specific disease.
Vaccination (Sept 2021): The act of introducing a vaccine into the body to produce protection from a specific disease.
A similar post was shared to Instagram in November 2021:
“Vaccine used to be defined as a substances that provides ‘immunity’ to a specific disease,” reads an Instagram post on November 4, 2021, that has received over 26,000 likes.
It continues: “Now, Merriam Webster has literally changed the definition of ‘vaccine’ and removed the ‘immunity’ portion in order to possibly cover for the fact that the Covid ‘vaccines’ don’t actually provide immunity from Covid.”
More specifically, the Merriam-Webster dictionary revised its definition of vaccine to replace the word immunity with “immune response.”
Vaccine skeptics have claimed that these changes were introduced to “accommodate” shortcomings of the COVID-19 vaccines.
The Facts
While it is true that both the CDC and Merriam-Webster did change their definitions of the words vaccination and vaccine, respectively, experts say that this is a problem of semantics rather than science.
“It’s an inconsequential red herring,” John P. Moore, a professor of microbiology and immunology at the Weill Cornell Medical College, told Newsweek. “It’s anti-vaxxers choosing to make an issue of something that isn’t real.”
Speaking about the Merriam-Webster definition, Moore said: “Immunity and immune response are basically synonymous terms for all practical purposes,” he said.
Immunity, as defined by the CDC, is protection from an infectious disease. Meanwhile, the immune response describes the defensive reaction of the immune system in response to a disease or unfamiliar substance in the body.
Vaccines work by teaching our immune system how to recognize the organism that causes a specific disease—in this case, the SARS-CoV-2 virus. In the past, the majority of vaccines worked by exposing the subject to a deactivated form of the disease-causing organism itself.
More recent methods involve adding the material from a disease-causing organism into a modified version of a different, harmless virus that acts as a courier, bringing instructions to the immune system on how to fight the disease. This is how the AstraZeneca and Janssen/Johnson & Johnson vaccines work.
Now, a new vaccine technology has been developed that uses small messenger molecules that directly deliver instructions on how to spot the infection to our cells. These messenger molecules are known as mRNA, and they form the basis of both the Pfizer-BioNTech and Moderna vaccines.
The Merriam-Webster definition change was made mainly because its original definition was not broad enough to accommodate scientific advances in the field. In November 2020, an archived version of the dictionary’s website defined vaccine as “a preparation of killed microorganisms, living attenuated organisms, or living fully virulent organisms that is administered to produce or artificially increase immunity to a particular disease.”
The updated version reads as follows: “a preparation that is administered (as by injection) to stimulate the body’s immune response against a specific infectious agent or disease.”
“Merriam-Webster adds definitions and evolves existing ones to accurately report on how words are used,” Peter Sokolowski, editor at large for Merriam-Webster, told USA Today.
He added that the change in wording from “immunity” to “immune response” was done to provide a more “detailed description of how a vaccine actually works.”
Meanwhile, the CDC changed its definition to avoid misinterpretation.
“The previous definition could be interpreted to mean that vaccines were 100 percent effective, which has never been the case for any vaccine, so the current definition is more transparent and also describes the ways in which vaccines can be administered,” Belsie González, a senior public affairs specialist for the CDC, told USA Today.
In other words, these linguistic tweaks were designed to be informative, not sinister.
“Back in late 2020 when the first vaccine results came in, the success of protecting against even mild infections was very significant,” Moore said. “In retrospect, we should have all been a little more cautious of our language.”
He continued: “Since 2020, the extent of protection against mild infection has gradually decreased over time, but what has been sustained—and what vaccines are really intended to do—is to prevent severe disease and death. The vaccines have consistently retained their ability to protect against severe disease and death, which makes it a success.”
So why have we seen this reduction in protection?
“The reason is twofold,” Moore said. “Firstly, protection against infection is predominantly mediated by neutralizing antibodies. These peak after about four weeks [following vaccination] and then gradually decline. This is a natural feature of the immune system. So as these antibody levels decline, they eventually go below the threshold needed to protect against mild infection, but not below the threshold to protect against severe disease and death.”
Moore added that this natural waning of our antibody levels against SARS-CoV-2 can be brought up again by a booster shot.
“The second factor is that the coronavirus varies its protein sequences, and one of the major drivers of this variation is resistance to neutralizing antibodies,” he said. “So as the virus is diversified, it has become more resistant to neutralizing antibodies, and therefore protection is lower. That doesn’t mean it is nonexistent—there is still a benefit—but the protection is lower than it was in late 2020.”
However, booster vaccines are still important for people who are most vulnerable to severe COVID-19 infections, Moore said. “Age is an influence, as are immunocompromising conditions, general poor health, asthma, obesity, etcetera.”
The Ruling
Misleading material
While the CDC and Merriam-Webster definitions of vaccination and vaccine were revised in 2021, the changes were not introduced to cover up shortcomings in the efficacy of the COVID-19 vaccines. Rather, they were introduced to provide clarity and avoid misinformation.
The issue is one of semantics, not science.
FACT CHECK BY NEWSWEEK
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