Logan Reed
There are a variety of vaccines available for the same disease, and they can differ in terms of their formulation, ingredients, and production processes. For instance, COVID-19 vaccines from Pfizer, Moderna, and Johnson & Johnson differ in their formulations and number of doses required. While the Pfizer and Moderna vaccines are mRNA vaccines that require two doses, the Johnson & Johnson vaccine is a viral vector vaccine that requires only one dose. Furthermore, influenza vaccines are made by multiple companies, each following different formulas and production methods. These differences in vaccine formulations can lead to variations in their effectiveness, side effects, and suitability for specific individuals.
| Characteristics | Values |
|---|---|
| Different formulas of the same vaccines | Vaccines that protect against the same disease but are produced by different manufacturers are usually not identical in antigen content or in amount or method of formulation. |
| Manufacturers use different production processes, and their products might contain different concentrations of antigen per dose or a different stabilizer or preservative. | |
| A mix-and-match vaccine policy can provide a stronger immune response and less confusion. | |
| The flu vaccine, for example, is made by six or seven different companies, following a variety of formulas and production methods. | |
| The three COVID-19 vaccines available (Pfizer, Moderna, and Johnson & Johnson) are all a little different but have the same goal of protecting against severe illness. | |
| There is no evidence to suggest that the COVID-19 vaccines currently in use in the U.S. have changed their formulations. | |
| There is no evidence to support claims that the ingredients and formulas of the COVID-19 vaccines have changed over time. |
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What You'll Learn
- COVID-19 vaccines: no evidence of formula changes
- Influenza vaccines: made by different companies, following different formulas
- Polio vaccines: first administered as a shot, then boosted with a different oral formulation
- Flu shots: debate over removing the last fraction of vaccines that contain thimerosal preservative
- Vaccine combinations: FDA-approved combinations are safe and effective
COVID-19 vaccines: no evidence of formula changes
A TikTok video falsely claims that the ingredients and formulas of the COVID-19 vaccines have changed over the last several months. However, there is no evidence to support these claims. In fact, once a COVID-19 vaccine has been granted an Emergency Use Authorization (EUA) or is formally licensed and distributed for human use, its ingredients and formulation cannot be changed.
Pfizer spokesperson Keanna Ghazvini and J&J spokesperson Richard Ferreira have both confirmed that the formulas and ingredients in their respective companies' COVID-19 vaccines have remained unchanged since their EUA issuance. Recent fact sheets containing ingredient lists for Pfizer and Moderna's two-dose vaccine, as well as J&J's single-shot vaccine, are publicly available on the FDA's website. Aside from the exact dosages listed for Pfizer's Comirnaty, there are no differences in terms of ingredients between the earliest and most recent fact sheets.
Furthermore, any major changes made to a vaccine or drug require "the submission of data, based on adequate and well-controlled clinical studies demonstrating safety and effectiveness," which must then be approved by the FDA. While updated COVID-19 boosters have been authorized, they were tested for effectiveness in mice and received FDA approval before data could be gathered from human trials. This was due to the pressing need to address the rapidly changing nature of coronavirus variants.
It is important to note that mRNA vaccines, such as the Pfizer and Moderna vaccines, cannot alter or modify a person's genetic makeup or DNA. The mRNA from a COVID-19 vaccine never enters the nucleus of the cell, where our DNA is kept. Instead, it works with the body's natural defenses to safely develop protection against the disease.
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Influenza vaccines: made by different companies, following different formulas
Seasonal influenza vaccines are designed to protect against the three influenza viruses expected to be most prevalent in the upcoming season. There are three FDA-approved flu vaccine production technologies used in the United States: egg-based, cell-culture-based, and recombinant flu vaccines.
The egg-based manufacturing process has been used for over 70 years and is the most common way to make flu vaccines. This process involves injecting candidate vaccine viruses (CVVs) into fertilized chicken eggs and incubating them for several days to allow the viruses to replicate. The fluid containing the virus is then harvested, and the vaccine viruses are inactivated and purified for flu shots, or used to make live, weakened viruses for the nasal spray flu vaccine.
Cell culture-based flu vaccines are produced in cultured mammalian cells instead of chicken eggs. The CVVs are inoculated into the cultured cells and allowed to replicate for several days. The virus-containing fluid is then collected, and the virus antigen is purified, inactivated, and tested. This process does not require chicken eggs and no animals are harmed.
Recombinant flu vaccines are produced using recombinant virus technology, which does not require an egg-grown vaccine virus or chicken eggs in the production process. The DNA for the hemagglutinin antigen of the influenza virus is added to a baculovirus, which is then used to infect cultured insect cells. These cells then produce the hemagglutinin protein.
Different companies produce influenza vaccines using these various production technologies and formulations. For example, Sanofi Pasteur manufactures the split virus inactivated vaccines Vaxigrip and Vaxigrip Tetra, while GlaxoSmithKline produces Fluarix and Flulaval, which are also split virus inactivated vaccines. AstraZeneca makes Fluenz and Flumist, which are nasal attenuated vaccines.
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Polio vaccines: first administered as a shot, then boosted with a different oral formulation
The first polio vaccine was created in the early 1950s by US physician Jonas Salk. The Salk vaccine, also known as IPV (inactivated polio vaccine), is administered via injection and confers IgG-mediated immunity in the bloodstream, protecting the motor neurons and eliminating the risk of bulbar polio and post-polio syndrome. This vaccine was developed using three wild, virulent reference strains of poliovirus (Mahoney or type 1, MEF-1 or type 2, and Saukett or type 3), which are grown in a type of monkey kidney tissue culture and then inactivated.
While the Salk vaccine was a significant advancement in the fight against polio, it had some limitations. Interest in developing a new type of polio vaccine remained high, especially outside the United States. This led to the creation of the oral polio vaccine (OPV) by physician and microbiologist Albert Sabin. Sabin's vaccine was live-attenuated, meaning it used a weakened form of the virus, and could be easily administered orally as drops or on a sugar cube.
The oral polio vaccine had several advantages over the injected Salk vaccine. Firstly, it was easier to administer, eliminating the need for sterile syringes, making it more suitable for mass vaccination campaigns. OPV also provided longer-lasting immunity than the Salk vaccine as it offered both humoral immunity and cell-mediated immunity. Additionally, OPV interrupted the chain of transmission, making it a powerful tool to stop polio outbreaks.
During the late 1950s and early 1960s, several large-scale human trials were conducted for the oral polio vaccine. By 1958, the National Institutes of Health determined that the OPV produced using the Sabin strains was the safest. Countries like Hungary, Czechoslovakia, and later Cuba, adopted OPV in their nationwide immunization programs, becoming the first countries to eliminate polio.
Today, in the United States, only IPV has been used since 2000 to eliminate the risk of polio variants associated with OPV. However, OPV is still used in many other countries, where children receive doses orally as part of their routine immunization schedules.
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Flu shots: debate over removing the last fraction of vaccines that contain thimerosal preservative
Flu shots have been a topic of debate due to the presence of thimerosal, a preservative that has been falsely linked to autism and other neurodevelopmental disorders. Thimerosal has been used in certain vaccines since the 1930s and is added to multi-dose vials of flu vaccines to prevent bacterial contamination. While studies have shown no evidence of harm, some groups have continued to raise concerns about its presence in flu shots.
In 2025, the Trump administration's vaccine advisers brought up the old debate and recommended that only thimerosal-free flu shots be administered. This recommendation was based on the false claim that thimerosal was linked to autism, a claim that has been refuted by studies and experts. According to the CDC, 96% of all flu vaccines administered in the US during the previous fall and winter were already thimerosal-free.
The decision to withdraw the recommendation for flu vaccines containing thimerosal was made by Health Secretary Robert F. Kennedy Jr., who named vaccine advisers to the federal Advisory Committee on Immunization Practices. Among the advisers was Lyn Redwood, a former leader of an anti-vaccine group, who claimed that thimerosal was dangerous and toxic, especially to children, pregnant women, and other adults. However, a CDC staff analysis showed no link between thimerosal and autism or other neurodevelopmental disorders.
The thimerosal decision primarily affects a small fraction of the population who receive flu vaccines in multi-dose vials, such as in nursing homes or mobile clinics serving remote areas. While the preservative is still allowed in vaccines, insurance companies are no longer required to cover them. This means that flu vaccines containing thimerosal may not be accessible to Americans who rely on insurance coverage.
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Vaccine combinations: FDA-approved combinations are safe and effective
There are several vaccines available for COVID-19, and they all have the same goal of protecting against severe illness, hospitalisation, and death from COVID-19. However, each vaccine is slightly different in its formulation and mechanism of action.
The Pfizer and Moderna vaccines are mRNA vaccines that received emergency use authorisation (EUA) from the FDA for use in the United States. These vaccines use messenger RNA (mRNA) technology to instruct cells to produce a protein similar to the coronavirus' spike protein, triggering an immune response. The Johnson & Johnson vaccine, on the other hand, is a viral vector vaccine that requires only one dose.
While the ingredients may differ slightly between vaccines, they work together to ensure effectiveness and stability. The mRNA is the key component, but lipids, or fats, also play an important role in delivering the mRNA to cells. Other ingredients like potassium chloride, sucrose, and acetic acid help maintain the pH and stability of the vaccine.
The FDA closely monitors the safety and effectiveness of COVID-19 vaccines and has advised manufacturers to update their vaccine formulations to match circulating SARS-CoV-2 variants for the 2025-2026 season. The FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) recommended a monovalent JN.1-lineage vaccine composition. This recommendation was based on a thorough review of manufacturing timelines, virus variant data, vaccine effectiveness, and immunogenicity data.
It is important to note that any changes to a vaccine's formulation or ingredients require rigorous testing and approval by the FDA. The FDA's fact sheets for the Pfizer, Moderna, and Johnson & Johnson vaccines detail the ingredients and dosages, providing transparency to the public.
In summary, while there are different formulas of the same vaccine type, such as the various COVID-19 vaccines, FDA-approved combinations are safe and effective. These vaccines have undergone rigorous testing and review, ensuring consistency and safety in their respective formulations.
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Frequently asked questions
Yes, there can be different formulas of the same vaccine. For example, the flu vaccine is made by six or seven different companies in the US alone, each following a different formula. Similarly, there are three different COVID-19 vaccines available, each with a slightly different formulation but with the same goal of protecting against severe illness.
Yes, it is safe to mix and match different vaccine types. In fact, early research has shown that giving people a different type of booster shot from their original vaccine type can provide a stronger immune response than giving an extra dose of the same vaccine.
Vaccination providers should not combine separate vaccines into the same syringe unless mixing is indicated for the patient’s age and is explicitly specified on the FDA-approved product label inserts. Only two combination vaccines, DTaP-IPV/Hib vaccine and Hib-MenCY vaccine, contain separate antigen components for which the FDA approves mixing by the user.
Different formulas of the same vaccine are expected to have comparable or equivalent efficacy. The FDA generally licenses a combination vaccine based on studies demonstrating that the product’s immunogenicity (or efficacy) and safety are comparable to monovalent or combination products licensed previously.
