Talk to Patients About: Vaccines and Residual Materials


Vaccines are scientifically proven to be safe and effective, so anti-vaccination efforts tend to steer the public away from science and data and toward unfamiliar aspects of vaccines that may sound scary.

One frequent distraction involves residual materials – small amounts of the ingredients used to make the vaccine. Residual materials are closely related to vaccine additives, the inactive substances that help preserve the vaccine or boost patients’ immune response, for instance. (See “Talk to Patients About: Vaccines and Additives,” May 2021 Texas Medicine, page 47,

Together, residual materials and additives help make up what are called excipients – basically those ingredients besides the weakened or dead viruses or bacteria in vaccines (

There are three main types of residual materials:

• Cell culture materials, such as egg protein, which is used to grow the vaccine antigens;
• Ingredients like formaldehyde used to kill viruses or deactivate toxins; and
• Antibiotics like neomycin used to prevent contamination of the vaccine by bacteria.

Most residual materials are harmless because they appear in such trace amounts that they have no health impact, says Charles Andrews, MD, director of clinical research at Diagnostics Research Group in San Antonio, which conducts clinical trials on vaccines.

While a handful of residual materials – like egg protein, antibiotics, and latex – can trigger an allergic reaction even in tiny amounts, those products are in only a few vaccines, Dr. Andrews says. For instance, egg protein is mostly found in some influenza vaccines.

The most severe reaction caused by vaccines, anaphylaxis, is extremely rare, occurring in about one in 1 million vaccinations, the Centers for Disease Control and Prevention (CDC) says. Physicians routinely screen vaccine recipients for a history of allergies or adverse reactions to vaccines and are prepared to react with epinephrine in an emergency, Dr. Andrews says.

Patients with concerns about allergic reactions can talk to their physician about which vaccines might pose problems and get referred to an allergist, if needed, CDC advises.

The important takeaway for most patients: Catching a disease is far more risky than anything found in a vaccine.

“There’s just not any science to show that what’s in these vaccines now is inherently dangerous [for most people],” Dr. Andrews said.


Tex Med. 2021;117(6):47
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