Vaccine ingredients can seem strange to the non-scientist because making the vaccine first requires common laboratory procedures and chemicals (aka reagents) that you may have never heard of before. I’ve observed many concerns and misunderstandings online that originate from a lack of understanding of these preliminary steps to making, for example, vaccine viruses—like the one used in the measles component of the MMR vaccine.
ALL VIRUSES MUST BE INSIDE A CELL TO REPRODUCE
Measles is an example of a virus and we can think of viruses as obligate parasites: they must invade a cell in order to survive. They use the machinery of their host (i.e. human lung cells in the case of measles) to reproduce themselves and to be able to infect a new host. This means that in order for us to make the virus used in the vaccine, we must grow viruses in cells in the lab (or later on at a factory for mass production). Unfortunately, for the infant vaccines that are currently approved by the FDA, you cannot simply engineer a virus without cells (though this is a current line of research and trial). So, if you want to understand the components of our commonly used vaccines, you first have to learn a bit about how we grow cells in the lab and the reagents we commonly use to do this.
BASIC CELL CULTURE PRACTICES:
We call the practice of growing cells in a petri dish “cell culture” or “tissue culture.” Culture = grow. In order for cells to be cultured, you have to grow them in liquids that are packed with nutrients. We call this the growth medium (it’s the pink liquid in the photos to the right). Growth media (plural of medium) is packed with the nutrients needed for cells to grow: water, sugar (i.e. glucose), amino acids, salt, etc.
Cells also need signals to grow, called growth factors, which will activate the cell and tell it to divide and replicate. We get growth factors from another added component to the medium: serum. Serum is a component of blood. You can isolate it by spinning blood at high speeds, separating out the different components of blood: red blood cells, white blood cells, fat, and serum (also called plasma). The growth factors in serum is absolutely necessary to culture cells. Without serum, you will not be able to grow cells.
Most laboratories use a specific kind of serum that is optimal for growing cells in the lab: fetal bovine serum or FBS. The serum comes from a cow fetus that is specially prepared by science research companies and is extensively processed for quality control (it is imperative that the serum used in research and for vaccines is sterile). The cultured cells can tell the difference between serums from different animals/ages and will actually not grow if they don’t have the right serum. That is why FBS is used—cells readily grow in this serum while they will not grow in, for example, adult cow serum. A great explanation from Research Gate (my go to website for lab questions):
“Tissue cells are inherently suicidal and they require growth factors that not only stimulate replication but are generally required to tell the cell not to undergo apoptosis. Remember that most cells (differentiated or not) know were they are because of local tissue chemical signals; be it adhesion molecules or secreted factors. Without continued stimulus by these factors cells are hardwired to undergo apoptosis because they then sense they are growing in the wrong place (hence in oncogenesis it is not just unregulated replication but molecular mechanisms of overcoming apoptosis for invasion and ultimately metastatic spread). Fetal bovine serum is awash with hormones, paracrine, endocrine and autocrine growth factors which support cells – somewhere in this mix is likely to be a factor supporting survival of your chosen cells.”
We also commonly add antibiotics to our growth medium in order to prevent bacterial growth and contamination of our cell culture. Commonly used antibiotics are: penicillin, streptomycin, and neomycin. Adding antibiotics is really important because bacteria would rapidly grow in this nutrient packed soup (sometimes we call media soup because it’s so nutritious!) without the addition of antibiotics. If any bacteria grow in your cell culture, you have to throw the whole thing out—it’s completely ruined and can’t be recovered.
Common concern: amount of antibiotics and serum in vaccines Some people have legitimate concerns about antibiotics in vaccines. Some could be allergic to antibiotics. Some are concerned about too many antibiotics given to infants. First, the addition of antibiotics to both the cell culturing process and the final vaccine product is absolutely necessary. Most vaccines cannot be shipped from the factory and used right away: you need to be able to store them. Because of the other components necessary to keep the vaccine virus stable (i.e. sugar), there is a high risk for bacterial growth in your vaccine without the use of antibiotics.
It is also important to realize that before the final vaccine product is released, the virus has to be removed from the cells and isolated for packaging into the vaccine. During this isolation process, all cell culture reagents and cells are washed away. It has been found that after this washing process, there is less than 1 part per million of fetal bovine serum and antibiotic left (think about slicing a cake into a million pieces and taking less than a slice to eat: this is a very small amount!). For the final product, 25 mg of neomycin is added, for example, to the measles vaccine. A normal dose of neomycin given to a 1 year old is ~500 mg per day to treat a bacterial diarrhea. This means that the amount found in the final vaccine is 20 times less than one normal dose of antibiotic. This is a very small amount.
Common concern: production of serum for use in vaccine virus synthesis Fetal bovine serum (FBS) is widely used in ALL cell culture practices (not just for the use of vaccines) to provide the growth factors needed for cells to survive. As I said before, older animals are not rich in the growth factors needed to survive and thus cannot be substituted for FBS.
Some people are concerned about FBS because of the way in which serum is produced. It is taken from cow fetuses. Some people are ethically against the use of animals and in particular cow fetuses. As of 2015, there is no way to make synthetic serum (think TrueBlood). The only way to get the growth factors necessary to culture cells is through this process. Down the pipeline, there may be synthetic substitutes for serum: last year promising research came out of the University of Edinburgh—the first laboratory to make real, mature red blood cells from stem cells. Reports say that this may be ready for small clinical trial by 2016. As of now, there is no feasible or reliable substitute.
Take home message: If you would like better reagents, like synthetic serum that avoids the use of animals in research, the best thing you can do is to support basic science research funding. You can do this by electing officials with a track record of supporting science. We need your support to develop better methods!