Mother Knows Best: Let’s Talk Common Vaccine Concerns


As a mother with two young children, I can understand every parent’s concern for the health and safety of their children. It is important to know what information to trust, as parents make health decisions for their families. Through my training as an immunologist I learned how vaccines work at a detailed cellular and molecular level. Understanding how vaccines work increases my appreciation for their great value to society. I was, therefore, very happy to get my children vaccinated following the standard protocol recommended by my pediatrician. With diseases such as the measles often coming back in outbreaks (even as recently as 2019), and knowing that infants are particularly vulnerable to measles, I breathed a sigh of relief after the measles mumps and rubella (MMR) vaccine was given to each of my children. (MMR is one of the later vaccines on the schedule, with the 1st MMR dose given at 12 months of age).

Why do I trust my pediatrician and vaccine science?

The scientific process involves many experts, studying and working over many years. Vaccine development, in particular, can take decades. Scientists rely on empirical evidence, produced by rigorous and repetitive experimentation. Good science stands up after being vetted and replicated by many experts running many different types of studies. That rigorous process means that sometimes theories will change. Thus, the overall integrity of science is demonstrated when previously held theories are revised in light of more recent results.

In medical science, treatments need to be evaluated for their effectiveness in clinical trials. To discern treatment effects from normal variation within a population, clinical trials need to be large enough to represent a wide swath of people. Statistical calculations help determine what the size a clinical trial must be to ensure that positive results are not due to chance alone. (For example, the odds of always getting heads in a coin toss decreases as the number of times the coin is tossed.) Clinical trials also need to be derived from a random sample of a population, because selection bias could skew the results. Finally, distinguishing a treatment effect from random variation also requires non-treated, or placebo control comparator groups.

Understanding the requirements for good clinical trial design helps reveal the limitations of some studies promoted by vaccine skeptics. Problematic studies could include those using a very small sample size, evaluating a nonrandom sample of individuals, or using biased data collection methods, such as self-reporting instead of clinical assessment. Seeing websites share studies with those types of problems suggests that information circulated by anti-vaccination groups can often be misleading.

hands pipetting in a lab

A brief primer in immunology

The molecular parts of a pathogen (such as a bacteria or virus) that is recognized by the immune system is called an antigen. There are two main cell types within the immune system which are trained to recognize antigens: B cells and T cells.

B cells produce antibodies, which are secreted proteins that (like suction cup arrows) stick to pathogens found on the outside of cells (in blood, lymph fluid, or in tissues). By binding extracellular pathogens, “neutralizing” antibodies can prevent infection of cells in the body and thus limit the propagation of disease. By recognizing the tail-end of the antibodies (or the feather part of the suction cup arrow), other immune cells (called macrophages and neutrophils), act like trash collectors to engulf and degrade antibody-coated pathogens.

T cells can recognize cells infected with intracellular pathogens. The antigens recognized by T cells are small pieces of degraded viruses or bacteria (such as short strings of broken proteins called peptides) that are displayed on the surface of infected cells. There are a few different types of T cell responses. Cytotoxic T cells fight infection by killing infected cells to prevent further pathogen spread.  Helper T cells send signals to other T cells, B cells or macrophages to help guide the proper type of response to a particular type of pathogen.

Common Vaccine Concerns

Over the years, I have heard many concerns from friends and family members about childhood vaccines. Here, I address some of the most common objections and questions, supplying a scientific perspective that may help ease minds and build confidence in vaccines.

Do vaccines weaken our immune systems?

One common misperception is that vaccines could weaken the immune system. However, the opposite is true. Vaccines enhance our immunity to pathogens by eliciting immunological memory. The first time our immune system responds to a particular pathogen, the adaptive immune response is slow, taking about two weeks to produce fully effective B and T cell responses. However, due to immunological memory, the second time the immune system sees the same pathogen, the immunological response is much faster, larger, and more robust, taking days instead of weeks to become effective. In essence, vaccines are a training regimen that teaches and strengthens the immune system, preparing it for battle with the real invader. While a natural infection would induce a more diverse and vigorous immune response than a vaccine, natural infections also come with great risk of adverse events: including death, lifelong disability, and cancer. For example, before the measles vaccine was widely used, 400-500 people per year died of the measles in the United States. Now, the MMR vaccine has reduced that measles death rate to nearly zero, with outbreaks occurring when vaccination rates drop.

Is the vaccine schedule too aggressive for young children?

Another misconception is that the immune system could be overwhelmed by an aggressive vaccine schedule, receiving too many vaccines at the same time or in short succession. The adaptive immune system is incredibly diverse, consisting of trillions of T and B cells each harboring unique antigen receptors. Our bodies are capable of responding to many different antigens at the same time. Vaccines given in combination with each other are evaluated for safety and effectiveness. Combining multiple vaccines ensures induction of immunity as soon as possible to prevent disease, reduces the number of doctors visits needed, and limits stress to children (and to parents in the doctor’s office). Vaccine schedules are also adjusted based on efficacy data. For example, the chicken pox vaccine has proven to be most effective when given after one year of age.


In essence, vaccines are a training regimen that teaches and strengthens the immune system, preparing it for battle with the real invader.

Michelle Ols

What about the “extra” stuff in the shots?

There are also concerns about the additives or preservatives used in vaccines. Preservatives keep the vaccine from becoming contaminated. The preservative thimerosal, raised some concerns, because it contains mercury. Due to such concerns, after 2001, thimerosal was removed from all childhood vaccines.

Is vaccine injury common?

Effective vaccines are designed to trigger mild inflammation, bringing immune cells to the vaccine site to develop responses to the vaccine. Thus, vaccines will commonly cause mild side effects, such as pain and swelling at the injection site, or even fever and muscle aches.  Fortunately, severe adverse events (such as seizures or serious allergic responses) are exceedingly rare, and most resolve over time without long-lasting effects. The Centers for Disease Control (CDC), the Food and Drug Administration (FDA), and the World Health Organization (WHO) tracks adverse events that occur after vaccination to ensure vaccine safety. In the United States, suspected adverse events reported to the FDA and CDC are tracked by the Vaccine Adverse Event Reporting System (VAERS), even though not all suspected adverse events can necessarily be attributed to a vaccine. This detailed tracking information can be downloaded from the VAERS website.

Do vaccines cause autism spectrum disorder?

Importantly, the oft-cited anti-vaccination study claiming an association with the MMR vaccine and autism led by Andrew Wakefield has been clearly debunked. Wakefield’s study included only 12 children who had attended his son’s birthday party—not a random sample. He later admitted to fabricating the data in his study, and lost his medical license. Since then, more than 14 million children have been enrolled in multiple autism studies, showing no causal connection between vaccination and autism. One study of 30,000 Japanese children showed that autism cases actually continued to increase even after the MMR vaccine was no longer available to children there.

Scientific and medical evidence is clearly in favor of vaccination, not against it. Beyond the question of autism, many studies have compared vaccinated and unvaccinated kids, with very large sample sizes, showing positive health outcomes.

Do vaccines have aborted fetal material in them?

In terms of religious objections to vaccines, one of the main concerns is the use of cell lines derived from human fetal cells. To be clear, tissue from newly aborted babies is no longer used for current vaccine production. Cells lines, such as WI-38 and MRC-5, that continue to be used in the production of some vaccines (rubella, chicken pox and hepatitis A, shingles) have been propagated since the 1960s. Such cell lines have divided independently for years. Thus, as descendants of the cells originally taken from a fetus over 50 years ago, those cells used today are not themselves part of an aborted child.

young girl getting a bandage on her arm after a vaccine

The National Catholic Bioethics Center (NCBC) encourages pharmaceutical companies to develop future vaccines without the use of such cell lines, and when possible recommends avoidance of vaccines developed with them. However, the NCBC also states that people are “morally free” to use such vaccines due to the need to protect public health and the life and health of children.

Does “Big Pharma” just want my money?

There is a common lack of trust in pharmaceutical companies. People often think that for-profit institutions have inherent bias. Of course, such biases should be critically evaluated. However, we should also consider that producing unsafe and ineffective vaccines would be unprofitable and damaging to a company’s reputation. In the cases where vaccines have caused demonstrable harm, there has been wide public and scientific debate and reassessment. One such example was the tragic outcome from Sanofi Pasteur’s Dengue virus vaccine campaign in 2016, after which the WHO changed its recommendations for that vaccine. Likewise, an early rotavirus vaccine found in rare cases to be associated with intussusception (an intestinal issue that causes blockage) has since been replaced with a safer vaccine.

Who can we trust for information?

Many people also do not trust information coming from government organizations. It is the job of the CDC, the FDA and the WHO to promote public health and also to ensure consumer safety of vaccines and pharmaceuticals. Such governmental organizations are independent of pharmaceutical companies and are not funded by them. Rather, pharmaceuticals are heavily regulated to ensure safety. Drugs that are deemed to be ineffective, cannot be marketed, and if safety concerns arise after commercialization, they are pulled from the marketplace. Due to their widespread and pediatric use, safety standards for vaccines, in particular, are extremely high.

It is also helpful to remember that some groups opposed to vaccination benefit from advertising they receive on their websites, social media sites, and video channels. Such groups can also profit from donations from supporters, speaker fees, and book sales. Thus, anti-vaccine organizations themselves can be biased by financial incentives of their own.

Our responsibility to the vulnerable among us

From a public health standpoint, vaccination campaigns are important for protecting vulnerable people in our communities. When a majority of people in a community are vaccinated, people with compromised immunity are also protected. Cancer patients, pregnant women, and the younger siblings of school-age children are at high risk for complications due to infectious diseases, such as measles. The healthy among us can help those who are more vulnerable by getting ourselves vaccinated.

I hope some of this information can help you feel better about the safety and effectiveness of vaccines. You can find more detailed information and helpful resources collated by pediatrician Paul A. Offit on his website and in his books. While any medical intervention poses some risk, in the case of vaccines, the benefits greatly outweigh the risks.


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Michelle Ols
About the Author

Michelle Ols

Michelle Ols is an immunologist who has been working in the fields of autoimmune disease and immuno oncology research at biotechnology and small start-up companies in Cambridge, Massachusetts, since 2011. Dr. Ols holds a PhD in Cellular and Molecular Medicine from The Johns Hopkins University School of Medicine and completed a postdoctoral fellowship at Yale University.  Before graduate school, Michelle was a Fulbright Scholar in Heidelberg, Germany. She is married with two young children.
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