Vaccines are one of the most significant achievements in modern medicine, playing a crucial role in preventing diseases and saving lives. Developed through rigorous scientific processes, vaccines prepare the immune system to recognize and combat specific pathogens. Ever wonder how vaccines work or how vaccines are developed? Ridhima Monga, MD, an infectious disease specialist at OhioHealth, explains these processes, provides clarity on common vaccine misconceptions and highlights the importance of vaccines for both individual and public health.
How do vaccines work?
“Vaccines work by imitating an infection,” Dr. Monga explains. “They trick your body into thinking you are fighting an infection and producing antibodies which neutralize foreign substances.” Vaccines typically contain weakened or dead parts of bacteria or viruses — such as proteins or inactivated toxins — that are safe but still trigger an immune response. This approach provides immunity without exposing individuals to the actual disease. It enables your immune system to respond faster and more effectively if and when they encounter the actual virus or bacteria, preventing further illness or reducing its severity.
What is herd immunity, and why is it important?
Herd immunity occurs when enough people in a population are vaccinated, which makes it difficult for a disease to spread. “For example, if 90% of a population is vaccinated, the remaining 10% have a lower risk of getting infected because the disease has fewer chances to spread,” explains Dr. Monga. Because of this, achieving herd immunity is essential to protecting those who cannot be vaccinated, such as infants and immunocompromised individuals.
Achieving herd immunity requires high vaccination rates. For highly contagious diseases like measles, a population needs 94-95% immunity to effectively prevent outbreaks. While herd immunity is challenging to achieve for viruses that mutate quickly, like COVID-19, it remains crucial for more stable pathogens.
Booster doses have become a key component of maintaining immunity. As Dr. Monga points out, “Booster shots are especially necessary for viruses that mutate rapidly, like COVID-19. These updates help keep the immune system primed against new variants.” For viruses like measles, smallpox or polio, which are more stable, a single series of vaccine provides long-term immunity, whereas for flu and COVID-19, updated vaccines are needed periodically to keep your immune systems ready to combat circulating strains.
Vaccine development and testing process
Vaccines undergo extensive testing to ensure safety and efficacy. The development process typically spans one to ten years and involves several stages:
- Preclinical trials: Vaccine manufacturers perform initial testing on animal models to evaluate safety of the vaccine and immune response.
- Phase one trials: This is the first time humans are given the vaccine. Small groups of healthy individuals receive the vaccine to assess short term safety, like if there are side effects from the injection, and determine appropriate dosage.
- Phase two trials: Trials expand to a larger, more diverse group of people, focusing on safety, side effects, and immune response in different demographics.
- Phase three trials: Large-scale trials with thousands of participants, providing the data required to confirm efficacy of the vaccine and monitor side effects.
- FDA approval and manufacturing: These are the last steps to complete before the vaccine is available to the general population. After the vaccine is made available to the general population, manufacturers still continue to do vaccine safety monitoring to track rarer long-term side effects that may pop up.
During the COVID-19 pandemic, vaccine development accelerated significantly due to the global health emergency. “The groundwork for mRNA vaccines had been laid over decades,” says Dr. Monga. “This technology was not new; it was adapted quickly for COVID because the virus was spreading rapidly, and we had the resources and global collaboration to support it.” Dr. Monga further explains they were able to combine some of the trial phases, in part, because there were more people who had already been infected and were available to inject with the vaccine. The amount of test subjects is often one of the limiting factors for vaccine trials.
How mRNA vaccines work
There are many non-pathogenic or inactive parts, including fats and proteins, that make up a virus and are used in vaccines. The proteins of the virus are what the virus uses to bind to humans, code and replicate in the body. All the proteins needed for this are manufactured by the virus’ mRNA.
Dr. Monga explains, “mRNA vaccines deliver the genetic instructions for cells to produce the harmless viral protein. The body recognizes that protein and mounts an immune response against the virus. All of this happens outside of the nucleus of the cell. The mRNA doesn’t enter the nucleus of cell where our DNA is so it cannot modify our genes. After the mRNA delivers the instructions, your cells destroy it and get rid of it.”
In contrast, non-mRNA vaccines often introduce the viral proteins themselves into bodies to elicit an immune response. The mRNA vaccines introduce the mRNA responsible for making the viral proteins. This technology allows for faster development and adaptation to the virus, a promising advantage for rapidly mutating viruses like COVID-19.
Vaccine boosters, schedules and distribution
Vaccination schedules differ for children and adults because each group has distinct vulnerabilities. Children’s immune systems are still developing, and early immunization is critical to protect them from diseases that could be more severe in childhood. “Certain diseases, like chickenpox, have milder symptoms in children than in adults,” says Dr. Monga. “For children, vaccines are timed to ensure maximum protection when they are most susceptible.”
For adults, vaccines are adjusted based on age, health conditions, and lifestyle. Booster shots, such as for tetanus and COVID-19, help sustain immunity over time.
With multiple vaccine options for some diseases, choosing the most appropriate one can be confusing. According to Dr. Monga, “Factors such as availability, individual health needs, and doctor recommendations play a role. For instance, a doctor might recommend that some adults with higher immunity risks get combined Hepatitis A and B vaccines at the same time to avoid having to go through the vaccine response or set of vaccines twice.” Consulting your healthcare providers is essential for making informed vaccination choices based on personal health conditions and risk factors.
Your choice of vaccines may also differ by where you are located. For example, during the COVID pandemic, most US citizens had access to two or three different vaccines. However, because of financial issues and patent laws that differ by country, not all of the same COVID vaccines were available in other countries. Equitable vaccine distribution remains a pressing issue, especially in low-income countries. Factors such as cost, infrastructure, and vaccine hesitancy contribute to disparities in access. Organizations like the World Health Organization (WHO) work to address these gaps, but challenges persist. Dr. Monga emphasizes that “achieving global immunity requires global access to vaccines,” underscoring the need for international collaboration.
Common misconceptions about vaccines
Despite their history of success, vaccines are often surrounded by myths. One persistent myth is that vaccines cause autism, a claim repeatedly debunked by scientific studies. “There is no scientific basis for the idea that vaccines cause autism,” says Dr. Monga. “This misconception originated from a flawed study, but decades of research have shown vaccines to be safe and effective.”
Another misconception involves vaccine ingredients. Some people worry about additives, like aluminum, formaldehyde, antibiotics and others. The quantities of mercury, human serum albumin or other additives are very minuscule and not harmful to humans. Dr. Monga reassures that vaccine ingredients are “carefully regulated and present in amounts far lower than what we might encounter daily in our everyday foods and other consumables.”
The future of vaccination
The landscape of vaccines is constantly evolving, with research focusing on developing vaccines for diseases like HIV and cancer. The success of mRNA technology has opened new avenues for vaccine development, promising faster responses to emerging threats. “In the future, I’m hopeful that we’ll continue developing better vaccinations for other viruses and chronic diseases that we’ve not been able to combat yet. An HIV vaccine is a dream,” notes Dr. Monga.
Vaccines are a cornerstone of modern healthcare, protecting individuals and communities from devastating diseases. With rigorous testing, continuous innovation, and global cooperation, vaccines remain one of the most effective tools in public health. Understanding their benefits, debunking myths, and advocating for equitable access are essential steps toward a healthier world.
For more information on how to live a safe life after the pandemic, including what types of vaccines are best for you, listen to an episode of The Wellness Conversation here.