Vaccine Safety: Overview

Introduction

The Western medical establishment has long agreed that vaccines are a crucial tool for protecting public health, as they can prevent or mitigate historically devastating diseases such as diphtheria, tetanus (lockjaw), pertussis (whooping cough), polio, rubella, measles, mumps, hepatitis B, varicella (chickenpox), and influenza. In the United States, government organizations including the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA), most major medical associations, and the vast majority of practicing clinicians have invested significant energy in campaigns to convince people to keep their vaccinations (also known as immunizations) up to date. Public health officials also encourage adults to receive select vaccinations at specific life stages and under certain circumstances, such as before international travel.

Medical experts do acknowledge that vaccines, like any medicine, can cause side effects. Typically, any adverse reactions are mild and brief, but very rarely they can be more serious. Still, the scientific consensus holds that for most people, the benefits of recommended vaccines heavily outweigh the small risk involved. Health officials note that vaccines are rigorously tested before approval and their ongoing safety is carefully monitored.

However, some people challenge the mainstream view of vaccines and the wisdom of routine inoculation against certain common diseases. Such critics tend to claim that vaccine side effects are more common and more serious than acknowledged by the medical establishment, and also raise concerns about vaccine batches that have been contaminated or contain controversial ingredients. They therefore argue that vaccination should be a personal, considered decision and that mandatory vaccinations infringe on their rights.

Beginning in 2020, the coronavirus disease 2019 (COVID-19) pandemic brought much attention to the debate over vaccine safety. Issues facing scrutiny include the need for vaccines to control the spread of disease, how vaccine safety is assessed, and who should be vaccinated.

Understanding the Discussion

Autism spectrum disorder (ASD): A collection of neurologically based developmental disorders in which individuals have impairments in social interaction and communication skills, along with a tendency to have repetitive behaviors and/or narrow, often-obsessive interests. Anti-vaccination advocates have suggested a link between ASD and childhood vaccinations, but the scientific consensus rejects such claims.

Clinical trial: A scientific evaluation of a drug or vaccine to determine whether it is effective and safe, with several phases involving greater numbers of test subjects in each phase; early phase trials are typically done with lab animals and later ones with human volunteers.

Endemic: Describes a disease or pathogen that is present or usually prevalent in a particular population or geographical area at all times.

Epidemiology: The branch of medicine that deals with the study of the causes, distribution, and control of disease in groups of people.

Herd immunity: Refers to a significant proportion of a population becoming immune to an infectious disease because of exposure or vaccination decreasing the likelihood of spread.

Thimerosal: A mercury-based preservative used in some vaccines beginning in the 1930s.

Vaccine: A preparation that contains an antigen, typically consisting of whole disease-causing organisms (killed or weakened) or parts of such organisms, that is used to confer immunity against the disease that the antigen causes.

Vaccine hesitancy: The act of delaying or refusing a recommended vaccine for oneself or one's dependents despite the availability of services providing safe immunizations. While often driven by skepticism over vaccine safety, hesitancy may also be influenced by many other complex factors.

History

Controversies over vaccine safety have raged for as long as vaccines have existed. Until the eighteenth century, treatment for smallpox, an often-deadly disease, was limited to an eleventh-century Chinese technique called variolation, which involved rubbing pus obtained from a smallpox pustule into a scratch on an otherwise healthy individual so that person would develop immunity to the virus. In the early eighteenth century, Lady Mary Wortley Montagu introduced variolation to Western Europe from the Ottoman Empire, where it was common practice. Although Montagu faced bitter opposition from English doctors on religious, medical, economic, and sexist grounds, she eventually succeeded in convincing the royal family of the effectiveness of variolation. In 1796 the English doctor Edward Jenner developed the world's first vaccination, for smallpox, after observing that milkmaids who had contracted cowpox, a milder, related condition, were not susceptible to smallpox.

Deliberately exposing a patient to infected fluid to confer immunity worked, but the notion of deliberately introducing diseased matter into a healthy body provoked fear, skepticism, and sometimes even violence. Although Jenner was confident enough in the safety of his vaccine to inoculate his own infant son, in 1853, more than half a century after his landmark discovery, the English government was compelled to pass a law making vaccination mandatory for all its citizens. So persistent were the doubts about the safety and necessity of vaccination, however, that in 1898, the government dropped this requirement, although it continued to encourage vaccination.

Between Jenner's discovery of the smallpox vaccine in 1796 and 1980, when the World Health Organization (WHO) officially declared smallpox eradicated, new vaccines emerged for many other infectious diseases that have caused enormous suffering throughout human history. In the early 1950s, for instance, Dr. Jonas Salk (1914–95) of New York famously developed an effective vaccination for another disease of children: polio. That debilitating disease often left patients partially paralyzed (as in the case of President Franklin Delano Roosevelt), unable to walk and sometimes unable to breathe. Others included vaccines against rabies, plague, cholera, typhoid fever, diphtheria, pertussis, tuberculosis, tetanus, yellow fever, influenza, mumps, measles, rubella, and anthrax.

Ironically, the very success of vaccination efforts in causing once-dreaded diseases to fade into distant memories may have contributed to increasing concerns over vaccine safety. As fewer and fewer Americans witnessed firsthand the ravages of epidemic diseases such as measles (which claimed 120 deaths in 1989–91) and rubella (which, between 1964 and 1965 alone, caused deafness, blindness, heart disease, or cognitive impairment in about 20,000 newborns whose mothers had been infected with the virus during pregnancy), many began focusing more on the risks of vaccines than on the horrors of the diseases they prevented.

In response to growing concerns over vaccine safety, Congress passed in 1986 the National Childhood Vaccine Injury Act, which made mandatory the reporting of adverse health events following specific vaccinations and also established a no-fault compensation system for those injured by vaccines. In 1990 the Vaccine Adverse Reporting System (VAERS) was established to monitor the safety of all vaccines approved for use in the United States.

With national vaccine safety protocols in place, public health officials launched an aggressive campaign to promote vaccinations. In 1994 the Vaccines for Children (VFC) program was established to provide access to free vaccines for eligible children, and in 1995 several major pediatric and medical organizations endorsed a uniform childhood immunization schedule. By 1994 officials were able to certify the elimination of polio in the Americas, by 2003 they declared measles no longer endemic in the Americas, and by 2005 they declared rubella no longer endemic in the United States. Compliance with recommended vaccination improved dramatically with school-entry mandates for immunization.

These triumphs, however, did not end the controversy over vaccine safety. In 1999 the first rotavirus vaccine, which had been licensed only a year earlier, was pulled from the market because of its adverse side effects, specifically intestinal blockage, reported through VAERS. Public confidence in vaccine safety controls were further shaken in 2004 when the first Lyme disease vaccine, which the FDA had approved in 1998, was also withdrawn from the market amid a flurry of lawsuits against its manufacturer and increasing concerns of untoward side effects similar to the actual symptoms of Lyme disease.

The greatest controversy in the vaccine safety debate, however, has swirled around belief in a link between the MMR vaccine and autism spectrum disorder (ASD), an idea first proposed in 1998. The journal article was later retracted after the author's conflict of interest was revealed, and based on epidemiologic evidence gathered for numerous subsequent studies, the weight of scientific evidence does not support the hypothesis that the MMR vaccine causes ASD. Researchers have suggested that because the vaccine is administered to young children around the same age that ASD symptoms typically emerge, observers have attributed a causal link to what is more likely coincidental timing.

Beginning in 1999, at the same time questions began surfacing about the rotavirus, Lyme disease, and MMR vaccines, consumer advocacy groups mounted a campaign to ban thimerosal, a mercury-based additive, from vaccines. That year, the Public Health Service and the American Academy of Pediatrics recommended removal of thimerosal from child vaccines as a precautionary measure. Because mercury is a neurotoxin harmful to the developing central nervous system of fetuses and infants, some groups believed that thimerosal exposure from childhood vaccines might cause attention deficit hyperactivity disorder (ADHD), speech or language delays, and, in particular, ASD. In 2004 the Institute of Medicine's Immunization Safety Review Committee examined epidemiological data from the US, Denmark, Sweden, and the United Kingdom before concluding that evidence does not support a causal relationship between thimerosal-containing vaccines and autism.

Three key developments in the early twenty-first century shaped attitudes toward vaccine safety. First, the September 11, 2001, terrorist attacks and the subsequent anthrax scare increased public fears of bioterrorism. Concerns over vaccine safety became overshadowed by worries of inadequate national supplies of anthrax and smallpox vaccine. Second, government officials and scientists issued repeated, dire warnings about the possibility that the virus responsible for creating a fast-spreading epidemic of avian influenza ("bird flu") might cross the species barrier to infect humans. Faced with the prospect of a flu epidemic that could claim millions of human lives, safety concerns took a back seat to the urgent quest to create an effective vaccine to prevent such a global catastrophe. Finally, a 2005 study of more than 30,000 Japanese children definitively debunked, in the eyes of most scientists, the claim that the MMR vaccine could be responsible for rising rates of ASD worldwide. When the number of ASD cases continued to increase after the MMR vaccine was replaced with single vaccines, researchers concluded that the combined vaccine could not be responsible for triggering the disorder on a large scale. A 2014 meta-analysis involving 1.2 million children also found no causation or association between vaccination and ASD. Some skeptics continued to refuse to accept the scientific consensus, however.

The US government also took a number of actions on vaccine safety. In 2005 Congress saw the reintroduction of a bill that would amend the Federal Food, Drug, and Cosmetic Act to ban the use of mercury in vaccines. The Mercury-Free Vaccines Act stalled in the House Subcommittee on Health; reintroduced again in 2007 and in 2009, each bill met the same fate as the earlier version. In 2012 and 2013, the CDC's Advisory Committee on Immunization Practices (ACIP) implemented a number of revisions, including a recommendation that the flu vaccine is safe for all persons six months and older. The ACIP also recommended eleven- and twelve-year-old males should receive the human papillomavirus (HPV4) vaccine and that a single dose of the meningococcal vaccination should be administered to military recruits.

Meanwhile, vaccine skepticism surged again in the 2010s, boosted by social media. Conspiracy theories proliferated amid a general atmosphere of increasing public backlash against government, media, and scientific authority. In January 2017 President-Elect Donald Trump, who believed in a link between ASD and vaccination, appointed vaccine skeptic Robert F. Kennedy Jr. to head a commission to investigate vaccine safety.

Based on CDC data for 1998 to 2015, vaccination against MMR, diphtheria, tetanus, pertussis, polio, hepatitis B, varicella, and pneumococcal conjugate dipped around 2012–13 before climbing again. In 2017, over 70 percent of children between the ages of a year-and-a-half and three years old had received all their ACIP recommended vaccines, with the lowest rates being found among those who were uninsured, lived in rural areas, or were Black or Indigenous. Declines in MMR vaccination were linked to a measles outbreak in California in 2014–15 and another in New York in 2018–19. The trend may have also contributed to the numerous outbreaks of mumps observed in 2016 and 2017, with more than six thousand total cases reported each of those years, as compared to the few hundred cases per year seen from 2000 to 2005. In the wake of those outbreaks, about a dozen state legislatures attempted to repeal personal, moral, or philosophical exemptions from mandatory vaccination before school entry. California, New York, Mississippi, West Virginia, Connecticut, and Maine removed all exemptions except for underlying medical conditions. Often, these moves were met with vocal protest and backlash from vaccine skeptics.

Vaccine Safety Today

The global COVID-19 pandemic that emerged in early 2020 greatly intensified public attention to vaccines. As both the death toll and the economic impact of the highly transmissible viral disease mounted, an unprecedented international effort was launched to develop a vaccine in record time. More than 150 potential vaccines for COVID-19 were in some phase of clinical trials less than a year after the virus responsible was first identified. While many public health experts noted that an effective vaccine would play a vital role in combating the pandemic, the high-profile research also stirred much controversy over vaccination. Many people expressed concern that the unusually rapid pace of development and testing, as well as the relative novelty of the mRNA technology involved in several candidate vaccines, might cause safety issues to be overlooked, whether in the effects of the vaccines themselves or in the logistics of production or distribution. However, public health officials maintained that candidate vaccines were thoroughly and rigorously vetted according to proper scientific and medical standards.

Meanwhile, conspiracy theories and false rumors spread regarding both the origins of COVID-19 and the purpose of vaccination efforts. Anti-vaccination activists used such misinformation—which closely intertwined with general conservative backlash against government and scientific authority—to further stir fears about vaccine safety overall. A related challenge was the deepening politicization of COVID-19 and related issues, including vaccines.

While a few COVID-19 vaccines earned emergency approval in certain countries within just a few months, the rigorous testing process in the US took slightly longer. In December 2020 drug manufacturers Pfizer and Moderna announced that they had developed vaccines that were more than 90 percent effective at preventing patients from developing COVID-19. Both companies received emergency-use authorizations from the FDA for their vaccines for use in adults who had no history of vaccine allergy and whose immune systems were not compromised by medications or chronic medical conditions. Subsequent data collection continued to indicate that the vaccines were safe and effective; as with earlier vaccines, side effects tended to be mild, such as a low fever or soreness at the injection site. The Pfizer vaccine became the first to receive full FDA approval in August 2021.

As other vaccines also entered wide use, however, some significant safety concerns did emerge. A vaccine developed by British company AstraZeneca was put on hold or restricted by some countries in early 2021 due to rare occurrences of blood clots in people receiving the vaccine. Similar concerns developed over a vaccine by the company Johnson & Johnson (Janssen) that was approved by the FDA in February 2021, causing the FDA to briefly pause distribution that April. After an extensive review, the FDA and the CDC initially determined that the Johnson & Johnson vaccine was still safe and effective, with the known and potential benefits considerably outweighing the known and potential risks. However, in December 2021 the CDC advised the use of other COVID-19 vaccines over Johnson & Johnson's, and in May 2022 the FDA limited the use of the Johnson & Johnson vaccine after reporting nine recipients had died due to blood clotting.

These setbacks, along with controversy over vaccine mandates by the federal government and other authorities, helped fuel ongoing vaccine hesitancy. Vaccine skeptics also frequently asserted that serious side effects from COVID-19 vaccines were much more common than officially reported. Similarly, as the federal government sought to combat vaccine misinformation by pressuring social media platforms to suppress certain content, critics complained that this amounted to censorship that stifled valid debate over the safety and efficacy of the vaccines.

While the scientific consensus remained that COVID-19 vaccination was safe according to the best available data, some public health officials did increasingly acknowledge challenges in the vaccine surveillance system. Experts noted that VAERS and similar databases worked as they should in highlighting the rare but significant blood-clot issue with the Johnson & Johnson vaccine, but were slower to raise attention to other concerns such as the risk of myocarditis (heart inflammation) that eventually did earn official recognition. Some health professionals also worried that politicization of the issue could cause real adverse reactions to be ignored amid the preponderance of conspiracy theories and outright false claims. A report by the New York Times found that by April 2024, there had been approximately 13,000 federal claims filed for injury compensation related to COVID-19 vaccination, but only 19 percent had been reviewed at all, only 47 were approved, and only 12 had actually been paid.

Scientists also pointed out that it is naturally difficult to prove a connection between vaccination and a subsequent illness, especially when cases are rare. Furthermore, reported side effects from COVID-19 vaccines often overlapped with symptoms of COVID-19 itself, making it even more difficult to conduct high-quality research into possible adverse reactions. Meanwhile, health experts expressed frustration that many of the most vocal concerns over vaccine safety were based on falsehoods and that backlash against the COVID-19 vaccines boosted hesitancy around other types of vaccines as well.

These essays and any opinions, information or representations contained therein are the creation of the particular author and do not necessarily reflect the opinion of EBSCO Information Services.

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