This post is about those risks that vaccines do carry and that we can discuss in a rational way, as opposed to the fairytale risks that the anti-vaccine camp comes up with to vilify vaccinations.

Those who advocate vaccine use are often portrayed as denying any harm from vaccines and arguing that vaccines are completely safe, even that everyone should be given vaccines. This I think is an example of projection. Those in the anti-vaccine camp may become convinced of the absolute evil of vaccines, they then project the mirror image of this certainty onto vaccine supporters, warping the reasoned position taken into some sort of ideologically driven madness.

No-one I know who supports vaccine use argues that vaccines are completely safe, we realise that total safety is a naive concept, one that undermines the real discussion we must undertake based on relative safety and risk vs benefit.

I mentioned a few risks that can reasonably be discussed in this previous post. I’ll cover a few more here but must point out that the overall risks associated with vaccines are still lower than those associated with the diseases immunised against.

The first risk I’ll cover is intussusception with rotavirus vaccines. In the late 1990s a rotavirus vaccine RotaShield® was put into use, within months it was found that there was an increase in intussusception associated with the vaccine. Intussusception is a form of bowel obstruction that consists of the bowel folding in on itself. An investigation of the vaccine determined that this bowel obstruction was up to thirty times more likely in infants that had received the vaccine. On the back of this information the manufacturer voluntarily withdrew the vaccine from use.

As a result of this new Rotavirus vaccines are closely monitored for intussusception risk. The current Rotavirus vaccine used in New Zealand, Rotarix®, has been monitored and found to have a low risk of intussusception translating to between 0 and 4 extra cases of intussusception per 100,000 infants. It is noted that these are “extra” cases of intussusception as the background level has been found to be approximately 34 cases per 100,000 infants per year (ie the total number of cases would go from 34 to 38 per 100,000).

I found a paper published just prior to 2000 that estimated that the incidence of hospitalisation due to rotavirus was approximately 315 to 362/100,000 annually in New Zealand. A report from 2002 estimated that deaths from intussusception in developed countries (specifically the USA) might be approximately 4 deaths per 100,000 live births. Given this the risks associated with the vaccine are considered to be lower than the risks of the disease.

Moving on, MMRV vaccine is considered to come with an increased risk of febrile convulsions compared with the separate MMR and varicella (note the MMRV vaccine is not currently available in New Zealand). Febrile convulsions (or seizures) are seizures caused by high temperatures and are quite common in childhood. I have not been able to find any information that indicates febrile convulsions per se are a danger, normally these are caused by infections and it is the infection that is considered the dangerous component. As these infections are what are aimed to be prevented by the vaccine then it can be reasonably concluded that the risk from the vaccine is much less than that of the prevented diseases.

A recent interesting case of a vaccine side-effect was the increase in narcolepsy incidence in Finland for the H1N1 vaccine Pandemrix. A press release from the Finland National Narcolepsy Taskforce was recently released and noted:

“In all the cases examined, narcolepsy associated with Pandemrix vaccination has been identified in persons who carry a genetic risk factor for narcolepsy. Because of this very strong association with the genetic risk factor which regulates immune responses, narcolepsy is considered an immune-mediated disease”


“In addition to Finland, Sweden is so far the only other country which by using epidemiological research has confirmed an increase in narcolepsy cases associated with pandemic vaccination. In Sweden, too, the increased risk of narcolepsy has been observed specifically in children and adolescents. The added risk associated with vaccination was about three cases of narcolepsy in every 100 000 persons vaccinated.”

Finally and importantly:

“During the influenza season 2010–2011, 52 persons were treated in intensive care, and 13 succumbed. Most of these were unvaccinated. Combining the data on morbidity and mortality with data on vaccinations in the 2009–2010 pandemic season indicate that a swine flu vaccination taken in the pandemic season had  provided 75–88 per cent protection against the swine flu virus in winter 2010–2011. Based on these figures, it has been estimated that during the second wave, the swine flu vaccine prevented approximately 40 000 cases of swine flu.

The Task Force concurs with the European Medicines Agency’s estimate that, despite the unforeseen and deeply regrettable cases of narcolepsy, the overall benefit-risk balance remains positive.”

This is an important point to remember. Medicine is a risk benefit analysis, virtually all interventions carry an element of risk and we must use the available information to determine if the benefits outweigh those risks. In the case of this vaccine it was determined that the benefits were great enough.

Finally, there is a risk to immunodeficient individuals who receive live virus vaccines. This is seen in the case of the oral polio vaccine (OPV). It has been estimated that the risk of developing vaccine-associated paralytic poliomyelitis (VAPP) in the general population is approximately 1 in 2.4 – 13 million oral polio vaccine doses. As the vaccine is multi-dose this breaks down to a 1 in 750,000 risk after the first dose. Immunodeficient individuals are at a much greater risk, possibly as high as 1 in 100-200.

As noted previously, this information allows us to make a determination of the risks of the vaccine under each situation. As such the OPV is no longer recommended in areas where polio is under control and the population will not come into contact with the wild strain and immunodeficient patients are not given the vaccine.

A recurrent theme here is the evaluation of both the risks and the benefits of vaccines. One cannot be properly assessed without the other, over-emphasis of one side of the equation will lead to a biased conclusion and decisions that may be costly in terms of human life. I must stress however that this attempt at a balanced what occurs all the time in science, new information is always coming in and must be incorporated into the existing body of knowledge.

In some cases this results in the removal of vaccines from use (eg RotaShield®) or the restriction of their use (OPV). The charge that science is blind to the potential drawbacks of vaccines and vaccination programmes is simply false.

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