Vaccine hesitancy

Vaccine hesitancy is a complex public health phenomenon. It involves the delay in accepting vaccines or the refusal of them despite their availability and supporting evidence. This concept includes several different behaviors. Some people refuse all vaccines, while others only delay them. Some people accept certain vaccines but remain uncertain about others. This behavior is not just a personal choice; it has significant global consequences. The World Health Organization characterizes vaccine hesitancy as one of the top ten global health threats. This is because hesitancy often leads to outbreaks and deaths from diseases that vaccines could prevent.

Many different factors contribute to why people become hesitant. These factors are often context-specific and vary by time and location. Psychological factors play a large role in how people react. Some people experience a fear of needles or a distrust of public authorities. Others suffer from a lack of confidence in their healthcare providers. Complacency is another major factor. This occurs when a person does not see the value or the need for a vaccine. Convenience also matters, as easy access to vaccines can influence whether people get them. A lack of scientifically based knowledge about how vaccines are made can also contribute to these feelings.

One specific mechanism that drives hesitancy is a shift in how people perceive risk. As immunization programs become more successful, certain diseases become very rare. This success can lead to incorrect heuristic thinking. When people do not see diseases like Haemophilus influenzae B in their daily lives, they may lose their sense of how serious the illness is. This lack of personal experience reduces the perceived danger of the disease. Consequently, the perceived benefit of the vaccine also drops. On the other hand, some illnesses like influenza remain common. This can lead people to mistakenly believe the illness is non-threatening despite evidence of its danger.

Concerns about vaccine ingredients often focus on thiomersal and formaldehyde. Thiomersal is an antifungal preservative used in small amounts in some multi-dose vaccines. The body metabolizes thiomersal into ethylmercury and thiosalicylate. In 1999, the CDC and the AAP asked makers to remove it as a precaution. Most U.S. and European vaccines have since removed it, except for some influenza preparations. Trace amounts may remain at a maximum of one microgramme. This is about 2.5% of the daily amount considered tolerable by the WHO. Despite fears, there is no scientific evidence linking thiomersal to autism. In fact, autism rates increased even after thiomersal was removed from most vaccines.

Formaldehyde is another ingredient that sometimes causes concern. It is used in small concentrations to inactivate viruses and bacterial toxins. However, the amounts in vaccines are minuscule compared to what is already in the human body. The human body produces formaldehyde naturally and continuously. In fact, the body contains 50 to 70 times more formaldehyde than the greatest amount found in any vaccine. The body is also capable of breaking down both the natural and the vaccine-derived versions. There is no evidence linking these small, infrequent exposures to cancer.

History shows how misinformation can damage public health. In 1998, Andrew Wakefield published a paper in The Lancet regarding the MMR vaccine. He suggested a link between the vaccine and autism based on twelve children. This study triggered a decline in UK vaccination rates to 80%. However, it was later discovered that Wakefield had falsified his data. He had a major conflict of interest because he stood to earn up to $43 million per year selling diagnostic kits. The paper was fully retracted by The Lancet in 2010. Wakefield was eventually struck off the UK medical register for deliberate falsification.

Finally, some people worry about "vaccine overload." This is the idea that many vaccines at once might overwhelm a child's immune system. Scientists say this concept is biologically implausible. Vaccinated and unvaccinated children actually show the same immune response to other infections. Furthermore, modern vaccine design has actually reduced the immunological load. The total number of immunological components in the 14 vaccines given to U.S. children in 2009 was less than 10 percent of the amount in 1980. A 2013 study of 1,008 children found no correlation between autism and the number of antigens in vaccines.