Social media is calling bluff on the Centers for Disease Control and Prevention for modifying its definition of the words “vaccine” and “vaccination” on its website.

Before the change, the definition for “vaccination” read, “the act of introducing a vaccine into the body to produce immunity to a specific disease.” Now, the word “immunity” has been switched to “protection.”

The term “vaccine” also got a makeover. The CDC’s definition changed from “a product that stimulates a person’s immune system to produce immunity to a specific disease” to the current “a preparation that is used to stimulate the body’s immune response against diseases.”

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Some people have speculated that the unannounced changes were the CDC’s attempt to hide the fact COVID-19 vaccines are not 100% effective at preventing coronavirus infection. U.S. Representative Thomas Massie of Kentucky said in a popular tweet the CDC has “been busy at the Ministry of Truth.”

However, a CDC spokesperson told McClatchy News the “slight changes in wording over time … haven’t impacted the overall definition.”

The previous definitions could have been “interpreted to mean that vaccines were 100% 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,” the spokesperson said.

“It’s also important to note that the modifications to the definition of ‘vaccine’ don’t change the fact that vaccines and the act of vaccination has prevented millions of illnesses and saved countless lives,” the spokesperson said in an email.

There remains the misconception that COVID-19 vaccines were designed to prevent infections altogether, leading people to believe the vaccines aren’t working as they should when they learn about breakthrough infections among the vaccinated.

But the coronavirus vaccines are doing exactly what they were designed to do, which is to prevent severe disease, including the need for hospitalization, and death — even in the presence of more dangerous versions of the virus such as the delta variant.

While data show the coronavirus shots are preventing infections in many outbreak scenarios, the fact breakthrough infections are happening doesn’t suggest failure, experts say.

This story was originally published September 09, 2021 2:24 PM.

Katie Camero is a McClatchy National Real-Time Science reporter. She’s an alumna of Boston University and has reported for the Wall Street Journal, Science, and The Boston Globe.