Few medical advances in recent memory have sparked as much controversy as COVID-19 vaccines utilizing mRNA (messenger RNA). Currently, there are two such vaccines, from Pfizer-BioNTech and Moderna.e60dc2a1-f33c-4a05-9b50-8e3e8e5976290ddaa2fe-1650-408b-b05d-59ae77fe0de8 Novavax vaccine is the only non-mRNA COVID shot available in the United States.e60dc2a1-f33c-4a05-9b50-8e3e8e5976290ddaa2fe-1650-408b-b05d-59ae77fe0de8 Many scientists have celebrated the use of mRNA to fight COVID-19 , with the two researchers behind this advance winning a Nobel Prize in 2023. Most experts agree that mRNA vaccines saved millions of lives — by some estimates, as many as 2.5 million lives — during the COVID-19 pandemic.e60dc2a1-f33c-4a05-9b50-8e3e8e597629a2e09d97-addb-4241-9883-4e097f9205c6 But mRNA vaccines are facing criticism from some public figures, most prominently U.S. Heath and Human Services Secretary (HHS) Robert F Kennedy Jr., who question their safety and effectiveness.e60dc2a1-f33c-4a05-9b50-8e3e8e597629e57a3bd1-dd29-4790-ba85-2e689d37fd6f In August 2025, Kennedy canceled $500 million in government-funded research to develop a range of vaccines based on mRNA.e60dc2a1-f33c-4a05-9b50-8e3e8e5976294ff491cd-e8ae-4f4a-8582-f6949309ccaa
How Do mRNA Vaccines Work? How mRNA Vaccines Work “In the end, both older vaccines and the newer mRNA vaccines do the same thing: give the body a sneak preview of a germ that then helps build a defense against that germ,” says David Wohl, MD , infectious disease doctor and professor of medicine at UNC School of Medicine in Chapel Hill, North Carolina. Traditional vaccines inject weakened or dead germs, or parts of these germs, into the body to teach the immune system how to recognize these invaders should there be an actual exposure. This method is different from that used by mRNA vaccines. These newer vaccines rely on mRNA, a type of genetic material the body naturally makes and uses every day. Messenger RNA acts as a set of instructions, telling cells how to make specific proteins required for normal metabolic function. Vaccines that use mRNA train the immune system by sending a message (the “m” in mRNA) to some cells instructing them how to temporarily make one harmless part of a germ, like the “spike” protein on the virus that causes COVID-19. The immune system then learns to recognize and attack the real germ if it shows up later. The use of mRNA helped scientists develop COVID vaccines more quickly than had they relied on traditional vaccine-making methods. “Developing a vaccine that uses a weakened or dead version of the actual virus is a lengthy and costly process. An advantage of the mRNA vaccine platform is that the message to the cell can be easily changed in response to a new virus or variant,” says Dr. Wohl.e60dc2a1-f33c-4a05-9b50-8e3e8e5976292ddc580b-73fe-4e57-82a9-398e9ec35e46
mRNA Vaccines: Rushed or Well-Researched? Some critics of mRNA technology say that the process of developing and approving COVID vaccines was rushed and that research on the vaccines’ safety and effectiveness was inadequate. Most infectious disease experts counter that argument by pointing out that mRNA technology is not new; it’s just that most of the public had never heard of it pre-pandemic. Scientists have been developing and testing mRNA technology for over 20 years, investigating its potential use against a range of diseases, says researcher Emily Landon, MD , executive medical director of infection prevention and control and medical ethicist at UChicago Medicine in Illinois. “This isn’t a brand-new technology that nobody’s tried before,” she notes. In the past, many mRNA vaccines weren’t widely used simply because there were no urgent disease outbreaks to warrant their deployment, not because the technology was dangerous, says Dr. Landon. “The mRNA technology was known to be incredibly safe and incredibly flexible and quick to be able to use, which is why we used it to make the COVID-19 vaccine. There’s really no reason to be suspicious of this technology any more than you’d be suspicious of any medical treatment or technology — this is just a new way of doing things,” she says.
Are mRNA COVID Vaccines Effective? Are They Effective? Kennedy says that mRNA vaccines are inferior to the traditional kind because they don’t adequately prevent upper respiratory infections such as COVID-19 and the flu .e60dc2a1-f33c-4a05-9b50-8e3e8e5976290f01fd48-f6f5-4009-b317-0ddc1d2873f8 But no vaccine, mRNA or otherwise, can completely block infections, says Jake Scott, MD , infectious disease physician and clinical associate professor of medicine at Stanford Medicine in California. “The goal is preventing severe disease,” he says. “The clearest benefit of vaccination shows in mortality data: Unvaccinated people have substantially higher death rates during surges, especially in vulnerable populations,” Dr. Scott says. According to data from 2021 and 2022 covering the period dominated by the BA.4/BA.5 omicron variants, unvaccinated people were about 14 times more likely to die from COVID-19 compared with people who had received an updated booster. The data revealed that the vaccines provided strong protection against hospitalization and death.e60dc2a1-f33c-4a05-9b50-8e3e8e597629ffffe5c1-aa66-45c7-8b6e-5ad8e9d5627c Additionally, research published in 2024 showed that vaccinated people who get COVID-19 are less likely than unvaccinated people to develop long COVID , a condition marked by an array of new or lingering and sometimes debilitating symptoms.e60dc2a1-f33c-4a05-9b50-8e3e8e59762999a937d5-54c8-4875-9491-c528a51fd63b
Risks From mRNA COVID Vaccines Possible Risks “Serious events are rare,” says Scott about COVID-19 mRNA vaccination. These risks include: Severe Allergic Reactions Anaphylaxis is a rare but potentially life-threatening allergic reaction that can occur after any vaccine. It happens in approximately 5 people per one million vaccines.e60dc2a1-f33c-4a05-9b50-8e3e8e597629d2cb2662-eb56-4b64-a306-46cf0e991b12 Heart Inflammation Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining outside the heart) have been linked to the Pfizer vaccine, with the U.S Food and Drug Administration recently requiring a warning about these risks on the label.e60dc2a1-f33c-4a05-9b50-8e3e8e5976297f7e6d3b-f059-4c09-8602-f932a1bd93ad It’s estimated that 4 to 7 cases of myocarditis happen per 100,000 vaccine doses.e60dc2a1-f33c-4a05-9b50-8e3e8e5976292e2cad93-5df7-42ad-ae8a-53e0f39a9154 A study published in 2024 found an incidence of 5 cases of myocarditis and pericarditis per 100,000 cases. The incidence of those events due to COVID-19 infection was 20 times higher than those due to mRNA vaccination.e60dc2a1-f33c-4a05-9b50-8e3e8e597629e1fa0450-a81c-422f-83ed-12924a1860a6 “Myocarditis occurs mainly in males ages 12 to 29 but is usually mild and resolves [goes away] with treatment. COVID infection causes myocarditis more frequently and more severely than vaccination,” says Scott. “The immune system is complicated, and some people may overreact to a vaccine and get very sick or have an immune response that confuses a body part with the germ. These reactions are very rare and can be seen with all types of vaccines against many different infections,” says Wohl. “Pointing to rare serious adverse events following COVID-19 vaccination as a reason to not use the vaccine is like saying we should abandon penicillin since so many people have allergic reactions to it,” Wohl adds.
Long-Term Effects of mRNA COVID Vaccines “The COVID-19 mRNA vaccines have been given to millions of people across the world: old and young, pregnant and not pregnant, immunocompromised and immunocompetent,” says Wohl. “While we don’t have 20 years of data specifically on COVID mRNA vaccines, we have this huge scale of experience and know that these are very safe vaccines — HHS Secretary Kennedy is incorrect to state otherwise.” U.S. government agencies have multiple reporting systems in place (VAERS, VSD, BEST, v-safe) to monitor safety continuously and note “signals” of potentially related health issues, says Scott. “These detected myocarditis within weeks but no other serious signals. Vaccine side effects historically appear within two months, not years later,” he says.
Short-Term Side Effects of mRNA COVID Vaccines Common side effects of vaccination include: Injection site pain Fatigue Headache Muscle aches Fever “These usually resolve within one to two days,” Scott says.
Common Misconceptions About mRNA COVID Vaccines Common Misconceptions Here infectious disease doctors address some of the most common concerns they hear from patients: “It changes your DNA.” Not true. In fact, the mRNA never enters the nucleus of the cells, where DNA lives. There is no mechanism to convert RNA back to DNA, says Scott. Think of mRNA as “a Snapchat message to a cell” — it is temporary, says Wohl. “Spike protein stays forever.” Not true. Some people worry that in response to vaccination with an mRNA COVID vaccine, the body’s cells will produce “spike” proteins indefinitely, potentially resulting in unforeseen health consequences. But human cells only produce spike proteins for two to three weeks, Scott says, with no evidence of harmful persistence. “We don’t know the long-term effects.” Yes, we do. “We now have four years of data, millions of people, no late surprises. Vaccine effects show up within weeks, not years,” says Scott.
Research on mRNA Vaccines Beyond COVID New Research Underway Scientists around the world are using mRNA technology to research a host of treatments for emerging diseases. Their fast development and production time will be able to help fight new pathogens like bird flu, says Wohl. The research on mRNA is also ongoing for other infectious diseases, including: Genital herpes Hepatitis C HIV Influenza Norovirus The same technology has the potential to treat noninfectious diseases like cancer, activating the immune system to attack cancer cells.e60dc2a1-f33c-4a05-9b50-8e3e8e5976299ba21165-8816-4776-9315-8b6829757a19
The Takeaway Vaccines made using mRNA are a novel but well-researched technology that played a major role in bringing the COVID-19 pandemic to heel. The vaccine is highly effective in preventing severe COVID that leads to hospitalization and death. Serious adverse reactions can happen, but they are rare. Researchers around the world are working to develop new ways to use mRNA technology to treat a range of infectious diseases and many types of cancer.
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