Note: this post was originally written for parents, although it is certainly useful information for everyone!
Hi parents! Scientist here. I decided to write a long post about vaccines to help shed some light on how vaccines work and, hopefully, bring some clarity to topics of debate. The amount of misinformation about vaccines feels a little out of control to me. And no matter what you think about vaccines, it’s tough to wade through this information without a scientific background. FYI, my science background: PhD in developmental biology from Stanford University, postdoctoral research at UCSF on the molecular basis of brain development with an emphasis on a group of genes implicated in autism and other neuropsychiatric disorders, and I recently joined the faculty at CSUS where I teach molecular cell biology and will have a research program focused on the molecular basis of neurodevelopment and neuropsychiatric illness. Ok, on to the fun stuff. (It’s long because I wanted to be comprehensive and address all of the questions I usually get about vaccines.)
First, I ask that you read this with an open mind. Having an open mind is an integral quality of good scientists – it is the only way to objectively analyze data. (Open minds are wise minds!) I also want to add that this debate gets nasty, but in the end we all love our kids and want what’s best for them (as a mama of two, I get that). I am not judging, I do not feel that is my place as a scientist – my place as a scientist is to arm you with information and help you better understand that information.
Important vocabulary: pathogen = disease-causing bacteria or virus
Q: Ok, so what are vaccines? (I feel like this very basic question is often not clearly answered.)
A:Usually they are viruses or bacteria that have been modified so they cannot hurt you, but still look like pathogens to your immune system. That part is key. When a weakened pathogen (or “acelluar” pieces of a pathogen) enters your body your immune system responds by making antibodies that will bind specifically to that pathogen, and target it for destruction. Here’s the really cool part – our immune system makes cells called memory B cells that will stay in our body for a really long time (depending on how strong the vaccine is). These memory B cells are primed to make antibodies specific for that pathogen if you were to get infected again. This is important because our immune response can take a long time - long enough for pathogens to have debilitating and sometimes lethal consequences. If you have those B cells ready to go, your body makes specific antibodies that will get rid of the pathogen before it hurts you.
Q: What about the other scary sounding stuff in vaccines?
A:They are all there to make sure the vaccine stays safe and effective. And while they sound awful, they are all actually totally safe in the amounts present. For example, formaldehyde sounds scary, but did you know that it is a normal metabolic byproduct that your body produces in small amounts constantly? You produce more formaldehyde over a matter of minutes than you get from a vaccine. Another fun fact: there is 4-15 times more formaldehyde in a single apple than any one vaccine. And your body simply processes it and gets rid of it (again, it knows how since you are always producing it). Aluminum? Present in things ranging from organic pears to natural breast milk. One of the first things biochemistry students learn is that dose matters. Yes, large amounts of aluminum and formaldehyde are bad…but large amounts of water can be lethal. Oh, and mercury-containing thimerosol is no longer in early childhood vaccines because it was removed due to public outcry. However, there is still zero scientific data to suggest that thimerosol has any detrimental effects. In fact, the type of mercury in thimerosol is ethyl mercury, which is readily flushed from the body. The bad mercury that our body has a harder time getting rid of is methyl mercury (found in tuna).
Q: Why should you trust a big pharma who profits from vaccines?
A:My first answer is that you don't have to. There are a lot of scientists who have published research on the safety of vaccines that are not affiliated with big pharma and do not profit from the results of their findings. They are people like me – who became scientists because they wanted to help learn more about biology in order to diminish human suffering. We work for academic institutions, not big pharma. We ask questions without a vested interest in the answers. These are the scientists that can provide you with unbiased information. You can do a search for yourself on the largest database of scientific journals here: http://www.ncbi.nlm.nih.gov/pubmed
You will find that when you search for studies on autism and vaccines, of the hundreds of studies conducted, there is still no scientific data to suggest a link between the two. For example, every epidemiological study conducted on populations of children living in the same community has shown autism occurs at the same rate in vaccinated and unvaccinated children.
Q. What is currently thought to be the cause of autism?
A:It is currently thought that autism is a neurodevelopmental disorder that often begins in utero. Most of the autism risk genes identified affect how the brain develops during gestation. There were actually a couple of papers very recently published indicating specific mutations in a large number of candidate risk genes for autism (1, 2). There has also been research showing the influence of environmental factors like maternal antibodies that are present in the womb, which were identified by scientists at the UC Davis MIND Institute (3). Autism is a very complicated disorder, and we certainly don’t have all of the answers! But, again, there has been an overwhelming amount of time and money dedicated to investigating a potential link between autism and vaccines, and every study has come back with the same results: there is no data to suggest a link between autism and vaccines. In fact, the rates of autism are essentially the same in vaccinated and unvaccinated populations (in a recent study reported on here, there was a slightly higher rate of autism in the unvaccinated population) .
Q: Back to the big-pharma-makes-a-lot-of-money-argument.
A:Yes, they do. They make money on every drug they produce. I have opinions on big pharma’s business practices that I won’t go into now because it actually has nothing to do with the argument about vaccine effectiveness or safety. For better or for worse, our entire medical system is profit based (our entire economy is, actually). The people at the forefront of the anti-vaccination movement also make a lot of money. That is not why I don’t believe them, though. I don’t believe anti-vaccination proponents because of the absence of scientific data to support their claims. As a scientist, I only believe what the scientific data supports. I read research, not opinions. (That is not meant as a slight to anyone! I am simply stating my practices. I know that reading primary research papers can be like reading a different language if you do not have a science background, so I would not really expect any non-scientist to have this practice. It’s the same reason I don’t read economics papers. Bleh!)
Q: What about vaccine-related injury?
A:The overall risk is something like 0.003%. And the VAST majority of those 0.003% have minor allergic reactions. Severe allergic reactions can occur, though they are extremely rare. There have been a few cases of autoimmune disorders being triggered by a vaccine. It is not entirely clear whether the vaccine was actually the trigger because it could have been triggered by any pathogen. Importantly, people who are immunocompromised, meaning they have a weakened immune system (chemotherapy patients, HIV patients, genetic immune deficiencies, etc.), cannot be immunized because their immune systems are so weak that even the weakened virus might hurt them. All of these people fall into the class of people who should not get vaccinated and for whom herd immunity is so important!
Q: What is herd immunity?
A:It’s kind of basic math. Viruses cannot replicate on their own. They need to infect a host cell in order to replicate. If they don’t make it into a host cell, they will eventually die. Here's an easy example: a person infected with a virus walks into a room where there are 20 vaccinated people separating him from a single unvaccinated person. That virus cannot move from the infected person and replicate in any of the vaccinated people because once it gets into their bodies, those memory B cells start pumping out antibodies that kill it before it can replicate and spread. Therefore, those 20 vaccinated people make it harder for the virus to make it to the single unvaccinated person. If half of the people were unvaccinated, that virus would get to have a replication party in all of their cells and would have a much easier time surviving, multiplying, and spreading. Herd immunity is just a basic principle about how infectious pathogens spread. If someone tells you it doesn’t exist, you should be wary of any other scientific information they give you because it means that they have never taken or studied immunology or microbiology and are not qualified to have an educated discussion about those topics.
The tricky thing about vaccines and herd immunity is that herd immunity really only works when a high percentage of the population are vaccinated. If not, then viruses have an easier time spreading around our communities, putting at risk our neighbors who cannot be vaccinated (newborns, cancer patients, etc.), and who are also much more likely to die as a result of infection. That is why the scientific community is so scared. We feel that even a single death from a vaccine-preventable disease is a tragedy.
Q: Isn’t natural immunity better than vaccine-induced immunity?
A:Well, the immune response is stronger because the pathogens are not weakened, so if you make it through the illness you will, in theory, have a great supply of those memory B cells. The problem is that a lot of these vaccine-preventable pathogens can cause blindness, deafness, brain damage, paralysis, or death. I know of a mama who has a sister who contracted rubella while she was pregnant. Her baby was born blind and deaf because of the infection. So, yes, she now has great immunity to rubella. But she would give anything to have had vaccine-induced immunity prior to her pregnancy.
Q: Why do some vaccines not give lasting immunity?
A:Each vaccine has a varying degree of effectiveness. By effectiveness I specifically mean the quantity and quality of memory cells that will stick around in the immune system post-vaccine. For example, the smallpox vaccine gave immunity for 65 years whereas the pertussis vaccine only lasts for about 10 years. This is the purpose of boosters. Boosters essentially tell your immune system that it is still important to mount a defense against the pathogen, and replenishes your stock of memory cells.
Q: I heard a lot of adults are to blame for the current measles outbreak. Should adults get vaccinated, too?
A.Absolutely! If you are unsure of your immunity, you can talk to your medical provider about checking your titer (a measure of your immunity), or you can just get a booster. Even if you’ve had a booster, but can’t exactly remember when and your provider doesn’t do the titer test, getting another booster cannot hurt you.
Q: Why do babies often get fevers after being vaccinated?
A:Part of the natural immune response is the release of molecules called chemokines, which cause fever. As a mama, I know how scary it can be when your little one has a fever, but a post-vaccine fever is indicative of a robust immune response and means they are making great memory B cells. That does not mean you shouldn’t treat your baby’s fever! (Please consult your pediatrician on when you should treat your baby’s fever.)
Q: What’s up with vaccine shedding?
A:Vaccine shedding is something only possible with a live attenuated virus. This is different from the pertussis vaccine, for example, which is an acellular vaccine, meaning it contains various pieces of the pertussis bacterial molecules and is not infectious at all, cannot cause illness ever, and cannot shed. Again, a live attenuated virus is a weakened virus that reproduces so slowly that a normal immune system will take care of it before it causes any harm. If a person is immunocompromised, live attenuated vaccines cannot be used because their immune system might not be able to handle even a weakened virus. The nasal spray flu vaccine does have a risk of vaccine shedding because the vaccine is administered directly to the mucus membranes of the nose. Therefore, if that recently immunized person were to sneeze onto an immunocompromised person, there is a theoretical possibility that the attenuated virus could give that immunocompromised individual the flu. This is why it is recommended to stay away from immunocompromised individuals for a week after getting the nasal spray flu vaccine. Other live attenuated viruses are injected into muscle. Some of the weakened virus will get into the lymphatic system, which is where all that good immunity will happen (production of specific antibodies, effector cells, and memory cells that will stay around for a long time). From there, some of the vaccine can enter saliva and mucus, although it is going to be a much lower amount. I think this is why the CDC only has the recommendation to steer clear of immunocompromised individuals in the case of the nasal spray flu vaccine. BUT, and this is critical, the virus that would potentially be shed post-vaccine is the attenuated (weakened) virus that does not cause illness in a person with a normal immune system. This is why vaccine shedding does not cause disease EVER in a person with a normal immune system. It would essentially be like getting an ultra-tiny dose of a vaccine (not enough to even cause an appreciable immune response that would lead to acquired immunity). This is anecdotal, but when my daughter was newborn, my husband did not realize this about the nasal spray flu vaccine when he took our 2 year-old to the doctor…and he got him the nasal spray form of the flu vaccine. I’m happy to report that my newborn daughter did not get the flu. I actually wasn’t really worried; it’s a very minimal risk….but when a person is severely immunocompromised it is important to worry about any potential risk.
Q: If I have a baby that is too young for MMR, could a booster given to a breastfeeding mama give the baby passive immunity through antibodies present in the breast milk?
A:Passive immunity is the transfer of active antibodies from one person to another. This happens during pregnancy when antibodies present in mama cross the placenta to the developing fetus. I recently spoke to an immunologist friend about passive immunity through breast milk. I myself was considering getting the MMR booster to help my 7 month-old baby girl, but he said (sadly) it probably would not boost her passive immunity an appreciable amount (for a virus as strong as measles, anyway). There are five classes of antibodies (IgA, IgG, IgD, IgE, and IgM). The type that is most effective in preventing infection from something like the measles is IgG. These antibodies cross the placenta during pregnancy and give passive immunity to the baby when it is newborn. The primary type of antibody that gets into breast milk is IgA. It provides some protection, but it’s just not as great as IgG.
Q: If newborns get passive immunity from mama during pregnancy, why are they susceptible to illness?
A:Passive immunity only lasts for a short time. That’s because antibodies tend to not survive very long (a few weeks to a few months, on average). Unfortunately, the effector cells and memory cells that are responsible for making the antibodies in mama do not cross the placenta. The memory cells are the cell types that stick around for years to provide lasting immunity. I read a study that indicated 88 percent of babies of vaccinated mothers have passive immunity to measles at 4 months, and that number dropped to 15 percent by 8 months of age (4). Although, and this is important, the amount of antibodies acquired through passive immunity may not be sufficient to protect the baby from a strong pathogen.
Q: What about the alternative vaccine schedule versus the CDC recommended vaccine schedule?
A:I've never found evidence to support the alternative vaccine schedule. It is my understanding that it is something to make parents feel more comfortable. There are a lot of factors taken into account for the CDC schedule, which have to do with considerations like when the acquired immunity will be best. For example, MMR is not given until 12 months because they want to make sure that all passive immunity acquired from mama during pregnancy is gone by the time the vaccine is administered because those circulating antibodies would decrease the immune response to the vaccine. So MMR can be given at 6 months, but is better at 12 months...and I recently read a study indicating even a little tiny bit better at 15 months (5); but, you could possibly do the initial shot earlier than 12 months and then get the booster early if you are concerned about measles in your community (of course, talk to your doc about these decisions).
I hope this was helpful! Again, I have no financial interest in this debate. As the mama of a 7 month-old baby girl who is not old enough to have MMR, a 2 year-old little boy who only now has partial immunity, and as the stepdaughter to a wonderful man who spent his final 9 months severely immunocompromised due to chemotherapy, I am certainly emotionally invested in the debate. But as a scientist who has read thousands of pages of scientific research, I only want to help spread knowledge and quell fear.
1 Iossifov I, et al., The contributions of de novo coding mutations to autism spectrum disorder. Nature. (2014) 515(7526)
2 De Rubeis S, et al., Synaptic, transcriptional and chromatin genes in autism. Nature. (2014) 515(7526)
3 Bauman MD, et al., Maternal antibodies from mothers of children with autism alter brain growth and social behavior development in the rhesus monkey. Transl Psychiatry. (2013) 9;3
4 De Serres, et al., Passive immunity against measles during the first 8 months of life of infants born to vaccinated mother or to mothers who sustained measles. Vaccine. (1997) 15(6-7):620-3.
5 Hinman A., et al., Comparison of Vaccination with Measles-Mumps-Rubella Vaccine at 9, 12, and 15 Months of Age. J Infect Dis. (2004) 189