Vaccine hesitancy
Vaccine hesitancy is a delay in acceptance, or refusal of vaccines despite availability and supporting evidence. The term covers refusals to vaccinate, delaying vaccines, accepting vaccines but remaining uncertain about their use, or using certain vaccines but not others. Although adverse effects associated with vaccines are occasionally observed, the scientific consensus that vaccines are generally safe and effective is overwhelming. Vaccine hesitancy often results in disease outbreaks and deaths from vaccine-preventable diseases. Therefore, the World Health Organization characterizes vaccine hesitancy as one of the top ten global health threats.
Vaccine hesitancy is complex and context-specific, varying across time, place and vaccines. It can be influenced by factors such as lack of proper scientifically based knowledge and understanding about how vaccines are made or work, as well as psychological factors including fear of needles and distrust of public authorities, a person's lack of confidence, complacency, and convenience. It has existed since the invention of vaccination and pre-dates the coining of the terms "vaccine" and "vaccination" by nearly eighty years.
Although myths, conspiracy theories, misinformation and disinformation spread by the anti-vaccination movement and fringe doctors leads to vaccine hesitancy and public debates around the medical, ethical, and legal issues related to vaccines, there is no serious hesitancy or debate within mainstream medical and scientific circles about the benefits of vaccination.
Opposition to mandatory vaccination may be based on anti-vaccine sentiment, concern that it violates civil liberties or reduces public trust in vaccination, or suspicion of profiteering by the pharmaceutical industry.
Safety concerns
As with any medical treatment, there is potential for vaccines to cause serious complications such as allergic reactions, but unlike other interventions, vaccines are given to healthy people and so require a higher safety standard. Serious complications are extremely rare and much less common than risks from diseases they prevent. As the success of immunization programs increases, public attention may shift away from the risks of disease to the risk of vaccination, undermining public support for vaccination programs.The success of vaccinations has made certain diseases rare, and consequently led to incorrect heuristic thinking in weighing risks and benefits among the vaccine-hesitant. Once such diseases decrease in prevalence, people may no longer appreciate how serious the illness is due to a lack of familiarity with it, and become complacent. The lack of personal experience with these diseases reduces the perceived danger and thus reduces the perceived benefit of immunization. Conversely, certain illnesses remain so common that vaccine-hesitant people mistakenly perceive the illness to be non-threatening despite clear evidence that the illness poses a significant threat to human health. Omission and disconfirmation biases also contribute to vaccine hesitancy.
Concerns about immunization safety often follow a pattern. First, some investigators suggest that a medical condition of increasing prevalence or unknown cause is an adverse effect of vaccination. The initial study and subsequent studies by the same group have an inadequate methodology, typically a poorly controlled or uncontrolled case series. A premature announcement is made about the alleged adverse effect, resonating with individuals who have the condition, and underestimating the potential harm of forgoing vaccination to those whom the vaccine could protect. Other groups attempt to replicate the initial study but fail to get the same results. Finally, it takes several years to regain public confidence in the vaccine. Adverse effects ascribed to vaccines typically have an unknown origin, an increasing incidence, some biological plausibility, occurrences close to the time of vaccination, and dreaded outcomes. In almost all cases, the public health effect is limited by cultural boundaries: English speakers worry about one vaccine causing autism, while French speakers worry about another vaccine causing multiple sclerosis, and Nigerians worry that a third vaccine causes infertility.
Ingredients concerns
Thiomersal
is an antifungal preservative used in small amounts in some multi-dose vaccines to prevent contamination. Thiomersal is metabolized or degraded by the body into ethylmercury and thiosalicylate. In 1999, the Centers for Disease Control and the American Academy of Pediatrics asked vaccine makers to remove thiomersal from vaccines on the precautionary principle. Thiomersal has been cleared from all common U.S. and European vaccines, except for some preparations of influenza vaccine. Trace amounts remain in some vaccines due to production processes, at an approximate maximum of one microgramme, around 15% of the average daily mercury intake in the U.S. for adults and 2.5% of the daily amount considered tolerable by the WHO. The action sparked concern that thiomersal could have been responsible for autism. This is considered disproven, as incidence rates for autism increased steadily even after thiomersal was removed. There is no accepted scientific evidence that exposure to thiomersal is a factor in causing autism. Since 2000, parents in the United States have pursued legal compensation from a federal fund arguing that thiomersal caused autism in their children. A 2004 Institute of Medicine committee favored rejecting any causal relationship between thiomersal-containing vaccines and autism. The concentration of thiomersal used in vaccines as an antimicrobial agent ranges from 0.001% to 0.01%. A vaccine containing 0.01% thiomersal has 25 micrograms of mercury per 0.5 mL dose, roughly the same amount of elemental mercury found in a can of tuna. There is robust peer-reviewed scientific evidence supporting the safety of thiomersal-containing vaccines.Formaldehyde
Vaccine-hesitant people have also voiced concerns about the presence of formaldehyde in vaccines. Formaldehyde is used in small concentrations to inactivate viruses and bacterial toxins used in vaccines. Small amounts of residual formaldehyde can be present in vaccines but are far below values harmful to human health. The levels present in vaccines are minuscule when compared to naturally occurring levels of formaldehyde in the human body and pose no significant risk of toxicity. The human body continuously produces formaldehyde naturally and contains 50–70 times the greatest amount of formaldehyde present in any vaccine. Furthermore, the human body is capable of breaking down naturally occurring formaldehyde as well as the small amount of formaldehyde present in vaccines. There is no evidence linking the infrequent exposures to small quantities of formaldehyde present in vaccines with cancer.MMR vaccine
In the UK, the MMR vaccine was the subject of controversy after the publication in The Lancet of a 1998 paper by Andrew Wakefield and others reporting case histories of twelve children mostly with autism spectrum disorders with onset soon after administration of the vaccine. At a 1998 press conference, Wakefield suggested that giving children the vaccines in three separate doses would be safer than a single vaccination. This was not supported by the paper, and several subsequent peer-reviewed studies failed to show any association between the vaccine and autism. It later emerged that Wakefield had received funding from litigants against vaccine manufacturers and that he had not informed colleagues or medical authorities of his conflict of interest: Wakefield reportedly stood to earn up to $43 million per year selling diagnostic kits. Had this been known, publication in The Lancet would not have taken place in the way that it did. Wakefield has been heavily criticized on scientific and ethical grounds for the way the research was conducted and for triggering a decline in vaccination rates, which fell in the UK to 80% in the years following the study. In 2004, the MMR-and-autism interpretation of the paper was formally retracted by ten of its thirteen coauthors, and in 2010 The Lancets editors fully retracted the paper. Wakefield was struck off the UK medical register, with a statement identifying deliberate falsification in the research published in The Lancet, and is barred from practicing medicine in the UK.The CDC, the IOM of the National Academy of Sciences, Australia's Department of Health, and the UK National Health Service have all concluded that there is no evidence of a link between the MMR vaccine and autism. A Cochrane review concluded that there is no credible link between the MMR vaccine and autism, that MMR has prevented diseases that still carry a heavy burden of death and complications, that the lack of confidence in MMR has damaged public health, and that the design and reporting of safety outcomes in MMR vaccine studies are largely inadequate. Additional reviews agree, with studies finding that vaccines are not linked to autism even in high risk populations with autistic siblings.
In 2009, The Sunday Times reported that Wakefield had manipulated patient data and misreported results in his 1998 paper, creating the appearance of a link with autism. A 2011 article in the British Medical Journal described how the data in the study had been falsified by Wakefield so that it would arrive at a predetermined conclusion. An accompanying editorial in the same journal described Wakefield's work as an "elaborate fraud" that led to lower vaccination rates, putting hundreds of thousands of children at risk and diverting energy and money away from research into the true cause of autism.
A special court convened in the United States to review claims under the National Vaccine Injury Compensation Program ruled on February 12, 2009, that the evidence "failed to demonstrate that thimerosal-containing vaccines can contribute to causing immune dysfunction, or that the MMR vaccine can contribute to causing either autism or gastrointestinal dysfunction", and that parents of autistic children were therefore not entitled to compensation in their contention that certain vaccines caused autism in their children.