Myth: No Studies Compare the Health of Unvaccinated and Vaccinated People

I’ve heard this claim several times. Ever since I found out that it is not true, I have been amazed how it just keeps resurfacing. I would like to put this myth to rest. I am aware of at least seven original research papers and one meta-analysis (looking at another 6 randomised clinical trials or RCTs) published since 2009 which look at myriad aspects of general health, comparing large unvaccinated and vaccinated populations. I will lay them out below, but to put it shortly: vaccinated people are as healthy or healthier in all aspects compared to the unvaccinated. The vaccinated populations studied have fewer vaccine preventable diseases (may seem obvious, but nevertheless needs to be mentioned), fewer cases of asthma, fewer heart attacks, better birth outcomes, and higher cognitive scores than their unvaccinated counterparts. To note, the incidence of autism is also unchanged in populations with or without the MMR vaccine – more about that in a piece of its own, The great myth of vaccines and autism.

All studies listed at the end of this post

But before we get to the studies themselves, let’s talk briefly about…

What kind of studies are possible?

The biggest limitation to vaccine studies is connected to the vaccine health effect number one. Naturally, the main effect vaccines have on health is the prevention of the diseases they were developed for. Because of their significant contribution to our health, conducting a study where children would be assigned to a group that would not receive vaccines is unethical. Individual parents do have the right to choose not to vaccinate their children (in most parts of the world), but nowhere in the world would an ethical committee approve of scientists asking parents not to vaccinate children, even for the purpose of a study.

This is why the studies I will present below are largely observational – looking at populations and comparing the differences among naturally occurring groups of unvaccinated and vaccinated people. Many other studies on this topic, which are not directly comparing groups, rely on data derived through other methods, like vaccine efficacy and the rate with which the diseases spread in their presence vs absence. For instance, an impressive study from 2013 digitized massive amounts of US data since 1888. They estimate a total of 3 to 4 million deaths prevented in the US by vaccines. You can find a video with a graphical presentation of the vaccination effect on disease prevalence in New York Times: The Vaccination Effect: 100 Million Cases of Contagious Disease Prevented, and it has also been covered by the Science Based Medicine, here.

Another example is an article titled Ten Great Public Health Achievements, published in The Journal of American Medical Association, which estimates that

…the current childhood immunization schedule prevents approximately 42,000 deaths and 20 million cases of disease, with net savings of nearly $14 billion in direct costs and $69 billion in total societal costs.

However, most of the time when people express their concern for the health of vaccinated vs unvaccinated people, they aren’t actually speaking of the vaccine preventable infectious disease, which has largely been absent from much of the western world, thanks to herd immunity (read more about herd immunity here, or shortly put: it’s the effective limitation on the spread of disease when most people are immune and won’t pass the disease on to others). They worry about other potential effects on health, such as allergies, asthma, non-preventable infections, autoimmune conditions, etc general health. So let’s look at studies on those topics.

The indirect health effects of childhood vaccines

One German study from 2011 evaluated data from 17 641 children and adolescents and found that the prevalence of allergic diseases (such as skin conditions) and non-specific infections in children and adolescents was not found to depend on vaccination status. However, not surprisingly:

The lifetime prevalence of diseases preventable by vaccination was markedly higher in unvaccinated than in vaccinated subjects.

In another German study, from 2013, 1315 babies were followed from birth until they were 20 years old to study the development of asthma. They concluded that the vaccinated have lower rates of asthma compared to non-vaccinated.

To look at the situation in a very different part of the world where the proportion of vaccinated/unvaccinated people are nearly reversed compared to the western world, here’s a study 2011 from the Philippines, called The effect of vaccination on children’s physical and cognitive development, which finds:

…no effect of vaccination on later height or weight, but full childhood vaccination for measles, polio, Tuberculosis (TB), Diphtheria, Pertussis and Tetanus (DPT) significantly increases cognitive test scores relative to matched children who received no vaccinations. The size of the effect is large, raising test scores, on average, by about half an SD.

It is worth noting that vaccination rates in the Philippines are still relatively low, and the effects of the infectious childhood diseases themselves (referred to as ‘stunting and wasting’ in this study) are likely the biggest contributing factor to the lower cognitive scores of the unvaccinated children. To avoid socioeconomic confounding factors, the study did match the results for household characteristics.

Additionally, there is one older study from Nigeria in 1990 that followed the small groups of 25 vaccinated and 25 unvaccinated children. One child in the vaccinated group had a mild case of measles, whereas the stats for the unvaccinated children were as follows: 3 dead (from measles and tetanus) and 11 non-fatal cases of measles.

The flu vaccine

Considering the flu shot: firstly there are several studies on its beneficial effect on health of not catching the flu. Much depending on the year and the flu strains in circulation, it protects from infection at rates anywhere between 10% and 93% (see more over at the CDC for seasonal flu, or a meta-review on the swine flu pandemic). In addition, comparing unvaccinated and vaccinated people who do catch the flu, a study in 2014 found that vaccinated people were protected from its gravest effects. As reported on the study by Forbes:

study released this past week shows that among this season’s influenza patients sick enough to end up in their intensive care unit, 91% had failed to receive this year’s seasonal flu vaccine. And for those admitted to the hospital, but with less severe disease not requiring an ICU stay, 67% weren’t vaccinated.

On top of protecting from the flu, and connecting back to the overall health angle, a 2013 meta-analysis looking in total at 6735 patients also found that having the flu vaccine may lower the risk of heart attack, although the exact reason has not been pinned down. Reported by the Center for Infectious Disease Research:

Influenza vaccination may prevent cardiovascular events via avoidance of atherosclerotic plaque rupture or other forms of cardiac injury in a vulnerable patient and represents a simple once-annual protective therapy to reduce cardiovascular events. This finding has considerable clinical and health policy importance.

Comparing vaccinated and unvaccinated pregnant women

One group especially in the spotlight for flu vaccines are pregnant women. Firstly, it is important to note again that the flu shot provides important protection from… the flu. Due to the attenuated immunity, women are more susceptible to infections during pregnancy. Thanks to the variable degree of flu vaccination in the general population, here we actually have an easy time finding large groups of both, unvaccinated and vaccinated mothers-to-be for observational studies, and partly thanks to that, there is an impressive amount of research on the safety of the flu-vaccine in pregnancy.

The search ‘pregnancy AND influenza AND vaccine’ gives 878 articles on Pubmed (the most comprehensive life science journal database), 180 of which are review articles. Here a recent review as an example: Safety of seasonal influenza and influenza A (H1N1) 2009 monovalent vaccines in pregnancy – no health concerns.

 The test-populations are equally impressive – here one study from 2013 that studied about 75 000 vaccinated and 150 000 unvaccinated expectant mothers. Maternal Safety of Trivalent Inactivated Influenza Vaccine in Pregnant Women:

trivalent inactivated influenza vaccine during pregnancy was not associated with increased risk of adverse events in the 42 days after vaccination, supporting its safety for the mother.

This extensive amount of research has lead the health authorities to recommend the shot for pregnant women. There is a direct effect of protecting the mother (and to some degree the infant) from the flu – see a study of the 2009 pandemic in Japan, vaccination for pregnant mothers reduced their infection rate by 89% – but it doesn’t stop there.

Unborn babies benefit from mother’s flu shot

Interestingly, the effect of flu vaccines on the health of babies starts even before birth. Three studies have compared babies of unvaccinated vs vaccinated mothers, and they have found significant health benefits for babies whose mothers took the flu shot when they were pregnant – fewer miscarriages and higher birth weights. One study from 2010 looked at effects on pregnant women during the H1N1 pandemic in the UK, another from 2013 looked at 30 448 pregnant women in Argentina, and a third study from 2104 looked at 12 223 pregnant women in Canada. You can read more about the results as reported in The Science Daily Flu shot during pregnancy shows unexpected benefits in large study, and Global News CA Pregnant women who get flu shot reduce baby’s health risks:

The women who did get the flu shot were 25 per cent less likely to deliver a baby prematurely or with a low birth weight

[The] influenza vaccine is just as important as making sure you get enough iron, that you are not smoking, not drinking alcohol, that it’s part of how you improve your own health and your baby’s health.

New research is indicating even more potential health benefits for the baby from mother’s flu vaccine. In 2013 The Science Daily reported on how Flu in pregnancy may quadruple child’s risk for bipolar disorder:

In spite of public health recommendations, only a relatively small fraction of such [pregnant] women get immunized. The weight of evidence now suggests that benefits of the vaccine likely outweigh any possible risk to the mother or newborn.

A previous study, by Brown and colleagues, in a related northern California sample, found a threefold increased risk for schizophrenia associated with maternal influenza during the first half of pregnancy. Autism has similarly been linked to first trimester maternal viral infections and to possibly related increases in inflammatory molecules.

Update: In 2016, a fourth and by far the largest study of pregnant women and the flu shot was published. This study followed 60 000 mothers-to-be in Australia, and found that the flu shot may cut stillbirths by half. The researcher note that increased numbers of stillbirths follow influenza waves, and say that vaccination may prevent even more than half of these as reported by MedPageToday:

the protective effect between vaccination and stillbirths that we observed may be an underestimate of the true effect measure

I hope that this body of evidence of the large benefits from a flu vaccine gives mothers necessary reassurance and arms them with useful information on how to protect their own and their babies’ health during their pregnancy.

Health effects of childhood vaccinations and the flu vaccine have been thoroughly studied

Covered above are the studies that I’ve found so far on this topic. It is by no means an extensive list (I have not combed the Pubmed for all possible studies). Should anyone know of more, I am always happy to get a pointer to relevant research.

It is important that vaccines effects are well studied. Should there be an unexpected side-effect for our health, researchers would fight for the chance to report those findings – not only would they want to let people know, but such a novel finding (if based on solid data and afterward confirmed by independent groups of researchers elsewhere) would mean the world to their careers.

What the science has uncovered so far, is that vaccines may have additional beneficial effects on health, such as the positive impact on neonate health, perhaps even a protective effect in heart disease. The greatest health effect of vaccines, though, remains the drastic difference they have made for surviving childhood in good health for millions of children worldwide. I am deeply thankful for vaccines – I do not have to worry that my daughters would be crippled by polio, go deaf from measles, or lay weeks or months in coughing fits, struggling for their life in the grip of whooping cough. When I think of what it must have been like to be a parent in the beginning of the century, and what it still is for parents in large parts of the world, I am amazed at the privileged and protected life we are allowed to have in the western world today. I’ve found that becoming a parent turns a permanent emotional switch in your head, and ever since, this topic regularly chokes me up. Thanks vaccines.

For an idea on the main impact vaccines have had on our health, here an infographic from Forbes How Vaccines Have Changed Our World In One Graphic:

The data in this graphic come from the web site of the Centers for Disease Control & Prevention. It is a look at the past morbidity (how many people became sick) of what were once very common infectious diseases, and the current morbidity in the U.S.

If you are interested in reading more on vaccine topics, please check out my Immunization overview (there you can find all my infographics and pieces on vaccine ingredients, conflicts of interest, herd immunity, and psychology of vaccine discussions to mention a few).

Summary of the studies comparing vaccinated and unvaccinated populations

Adding more studies as I find them:

If you would like to have a discussion in the comments below, please take note of my Commenting policy. In a nutshell:

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