Vaccines are not dangerous

The hypothesis

Some people believe that vaccines contain dangerous and harmful substances, are not sufficiently monitored or in any case risky.

Scientific elements that contradict this hypothesis

The concept of vaccine safety can be divided into two different aspects:

1. The concept of safety as harmlessnes

If we base the concept of the safety of a vaccine on its harmlessness, any adverse event would make the vaccine ‘unsafe’. In general, by applying this definition, it can be said that no vaccine is 100% safe.

In reality, before being placed on the market, vaccines must pass rigorous analysis and even when they come into use the monitoring continues, through the reporting of adverse drug events. Thus, vaccines are effectively among the most controlled of all drugs available. The reporting of adverse events, managed in Italy by the Italian Drug Agency, allows us to know and precisely describe the harmfulness of vaccines.

In most cases these are mild reactions that resolve spontaneously (pain and redness at the injection site, or fever). In some rare cases, severe vaccine reactions may occur and it is not usually possible to predict which individuals might develop such a reaction. However, by following the guidelines to indicate when the vaccine can or cannot be used, the risk of side effects is minimised.

In any case, on close consideration, few things in life can be deemed harmless. Even daily activities have hidden dangers: in Italy every year domestic accidents cause at least 4,500 deaths, 130,000 hospitalisations and 1,300,000 arrivals at the emergency room1. Road accidents in Italy in 2010 caused 4,090 deaths and 302,735 injuries2. Cigarette smoking causes about 30,000 deaths a year from lung cancer. Yet a large number of those who do not want to vaccinate their children do not consider the hypothesis of not using a car or giving up smoking.

People sometimes fear activities that are not in fact dangerous and, on the other hand, do not fear activities that could have very serious consequences. That is, they tend to overestimate or underestimate the risk based on multiple factors. There are many factors that influence risk perception. Below is a list compiled by David Ropeik, a former professor at Harvard University and author of several books on risk3.

  • Confidence. The more we trust a particular person or behaviour, the less fear we will have, and vice versa.
  • Risk and benefit. The greater the benefit perceived to be associated with a choice, the less one tends to fear the risks associated with that choice.
  • Control. When we believe we have control over a situation - in a physical sense, but also in a psychological sense and regarding participation in the decision-making process - the situation becomes less frightening.
  • Freedom of choice. The situations in which we can choose whether and in what way to face a danger tend to be less frightening than those in which a similar risk is imposed on us from the outside (as is the case, for example, of environmental risks).
  • Natural or man-made. Natural hazards generally frighten us less than those arising from human activities. For this reason we perceive proximity to a factory as more dangerous than the food we put on the table, regardless of the actual assessment of the associated risks.
  • Terror. The worse the consequences (in terms of greater suffering) of a risk, the more it scares us. This is why cancer prevention has always been poorly followed: it is better to do nothing than to face the fear of the disease.
  • Catastrophic or chronic. The things that can kill many people at a specific time and in a specific place (such as a terrorist attack) are more frightening than those that cause the same number of chronic deaths, spread over space and time (like a disease or car accidents).
  • Uncertainty. The greater the uncertainty about the real extent of a risk, the greater the fear. Uncertainty can arise when there are no concrete data or when we are unable to understand them (invisible things are uncertain by definition and this explains the particular fear aroused by potential invisible risks such as electromagnetic waves).
  • Me and them. Regardless of the facts, any risk seems greater when we think it can affect us directly. It does not matter if it affects one in a million people if we fear that we may be that person.
  • Familiar or new. When we hear about a risk for the first time, and we do not know much about it, we are more afraid than when we have lived with the same risk for some time and the experience helps us to see it in perspective.
  • Children. We fear the dangers that affect children more than those that affect the adult population.
  • Personalisation. A risk associated with a specific person or a single factor (vaccine) terrifies us more than one that is statistically just as real, but which is only an abstract risk in our mind.
  • Fairness/morality. The risks that concern the poor, the weak and the disabled arouse more anger than those that affect the rich and the powerful. We are angered when those who are exposed to a danger do not reap any benefit from it.
  • Awareness. The more we are aware of a risk - thanks to the media but also to social contacts - the more we worry about it.

2. The concept of safety as the ability to protect from a real danger

If we use this concept of safety, the risk linked to the use of the vaccine must be significantly lower than the benefits deriving from its use (prevention of the disease onset). In other words, we need to evaluate the risk-benefit ratio of vaccines and see if it is favourable. In fact, even a rare side effect would not be justifiable if the vaccine held no benefit.

We assess the risk-benefit ratio of vaccines by comparing the risk from the disease with the risk associated with the use of the vaccine4.

Risks linked to disease Risks linked to vaccine

Pneumonia: 1/20
Death: 1/3000


Encephalitis: 1/300


Congenital rubella: 1/4 if contracted in early pregnancy


Encephalitis or severe allergic reaction: 1/1,000,000


Death: 1/20


Death: 3/100


Pneumonia: 1/8
Encephalitis: 1/20
Death: 1/20


Inconsolable crying then complete recovery: 1/100
Convulsions or shock then complete recovery: 1/1.750
Acute encephalitis: 0-10.5/1,000,000 Death: not proven

The table shows that a child is much more likely to be affected by one of these diseases than by any vaccine. That is, the benefits of vaccination far outweigh the mild risk inherent in vaccination itself. On the other hand, in the absence of vaccinations, many more deaths and complications would have occurred.


The production of vaccines is a very delicate process leading to their introduction only after a long period of study. Constant monitoring - both during the production phase and during use - makes vaccines among the safest drugs available on the market. The risks, however modest, linked to the use of vaccines must always be compared with their benefits.

Sources / Bibliography
  1. Dati dal Sistema Informativo Nazionale sugli Infortuni in Ambienti di Civile Abitazione (SINIACA), Istituto Superiore di Sanità.
  2. Dati ISTAT.
  3. Ropeik D. How risky is it, really? Why our fears don't always match the facts. McGraw Hill 2010.
  4. Dati dal Center for Disease Control (CDC).