Understanding the science behind vaccines, including what vaccines are made of, and how vaccines work with the body’s immune system, can help you begin to appreciate how they help prevent us from suffering from dangerous and sometimes deadly diseases.
How do vaccines work?
Viruses/Bacteria and Your Immune System
When viruses or bacteria (germs) invade your body, they attack and multiply. This invasion is called an infection, and the infection is what causes illness. The first time your body encounters a germ, it can take several days for your body to make and use all the tools it needs to fight the infection. After the infection is over, your body’s immune system keeps a few “memory cells” that remember what it learned about how to protect against that disease. If your body encounters the same virus or bacteria again, it will produce antibodies to attack the germ more quickly and efficiently.
How Vaccines Work
Vaccines are made up of viruses or bacteria that are altered or weakened so that they only cause an imitation of the disease and not the disease itself. There are a variety of different ways to alter or weaken the viruses or bacteria in vaccines so they cause immunity instead of serious disease. Following are the different types of vaccines and how they are created, including live attenuated vaccines, toxoid vaccines, inactivated vaccines, subunit vaccines and conjugate vaccines.
- Live, attenuated vaccines weaken the living viruses in the vaccine so they cannot cause disease in people. Since these types of vaccines are the closest to natural infections, they are very effective, but not everyone can get them. For example, people with weakened immune systems like those undergoing chemotherapy, should not get live vaccines. Examples of live, attenuated vaccines include MMR, chickenpox and the flu vaccine nasal spray also known FluMist.
- Toxoid vaccines prevent diseases caused by bacteria that produce toxins (poisons) in the body. Like in live, attenuated vaccines, the toxins are weakened so they cannot cause illness. Weakened toxins are called toxoids. For example, DTaP and Tdap vaccines contains diphtheria and tetanus toxoids, in addition to protection against pertussis.
- In inactivated vaccines, the viruses are inactivated (killed) when making the vaccine. By killing the viruses, the vaccines produce immune responses, but cannot cause the disease itself. Examples of inactivated vaccines include hepatitis A, influenza (shot only), polio (shot only) and rabies.
- Subunit vaccines use only a part of the virus or bacteria is included in the vaccine instead of the the full germ. Because these vaccines contain only the essential antigens and not all the other molecules that make up the germ, they cannot cause illness. The pertussis (whooping cough) component of the DTaP vaccine is an example of a subunit vaccine.
- Conjugate vaccines use part of the sugar-like coating of bacteria called polysaccharides. However, because young children don’t make a very good immune response to the sugar coating alone, the coating is linked (conjugated) to a harmless protein. This protein carries the sugar-like coating of the bacteria to certain cells in the immune system to which it would not have access on its own. Then, if the bacteria enters the body, the antibodies will recognize the sugar coating and keep the bacteria from causing disease. Although many conjugate vaccines were developed because of the need to protect infants and young children with immature immune systems, conjugate vaccines are recommended for all ages. Examples of conjugate vaccines include Hib, hepatitis B, HPV, DTaP, shingles, pneumococcal (PCV13) and meningococcal (MenACY).
To see an example of how vaccines work, read the story of Chip and Dale from the Vaccine Education Center at Children’s Hospital of Philadelphia (CHOP).
What is community immunity (herd immunity)?
Germs can travel quickly through a community and make a lot of people sick. If enough people in your community get a certain disease, it can lead to an outbreak. However, when enough people are vaccinated against a certain disease, the germs can’t travel as easily from person to person and the entire community is less likely to get the disease. Even if a person does get sick, there’s less chance of an outbreak because it’s harder for the disease to spread if a lot of people are vaccinated and therefore immune. Eventually, the disease becomes rare, and sometimes, it can be wiped out altogether, which is what happened with a very serious disease called smallpox. This is known as community immunity or herd immunity.
Community immunity protects everyone, and is especially important for people who are vulnerable to diseases, but who can’t be vaccinated. This includes children too young to be fully vaccinated, people with serious allergies against certain vaccine ingredients, and people with weakened or failing immune systems (e.g., people with cancer, HIV/AIDS, type 1 diabetes, or other health conditions.)
Community immunity is also important for the very small group of people who don’t have a strong immune response to vaccines. These people who cannot get vaccines or who aren’t protected from vaccines depend on a high level of immunization in their schools and/or their communities to help protect them against dangerous, and potentially deadly diseases.
Each vaccine-preventable disease requires a certain percentage of people in a community be vaccinated in order to prevent the disease’s spread. The exact percentage depends largely upon how easily a disease can spread from person to person.
Don’t infants have natural immunity from their mothers? And isn’t natural immunity better than immunity from vaccines?
Natural immunity occurs when a person is exposed to a disease, becomes infected and survives the infection. While it is true that natural immunity usually results in better immunity than vaccination, the risks to your child are much greater. Vaccines help develop immunity by imitating an infection, but this “imitation” does not cause illness. For example, a natural chickenpox infection may result in pneumonia or another serious complication, whereas the chickenpox vaccine might only cause your child to have a sore arm for a couple of days. Measles, meningococcal disease (meningitis), polio and many other vaccine-preventable diseases can kill your child, or leave him seriously debilitated for life.
Watch the following video of VYF Board Member Dr. Paul Offit as he explains why natural immunity can come at a serious price.
Even though your baby may get some immunity from you during the last few weeks of pregnancy, it is not long lasting. Your baby needs the long-term protection that can only come from making sure he receives all of his or her vaccines according to the CDC’s recommended childhood immunization schedule.
Even if you are breastfeeding your baby, he or she still needs to be protected with vaccines at the recommended ages. While breast milk provides important protection from some infections (colds, ear infections and diarrhea) as your baby’s immune system is developing, breast milk does not protect him or her against all diseases.
Do I have to vaccinate my baby if I’m breastfeeding him?
Yes, even breastfed babies need to be protected with vaccines at the recommended ages. While breast milk provides important protection from some infections (such as colds, ear infections and diarrhea) as your baby’s immune system is developing, breast milk does not protect him or her against all diseases. Even if your baby is being breastfed, she needs the long-term protection that can only come from making sure she receives all of her vaccines according to the CDC’s recommended childhood immunization schedule.
Why are diseases coming back?
Vaccine-preventable diseases never left. They still exist throughout the world, even in the U.S. While you might not see some of these diseases every day, they are still common in other countries and could easily be brought into the U.S. If we stopped vaccinating, the relatively small number of cases we have in the U.S. could very quickly become tens or hundreds of thousands of people infected with diseases.
Even if your family does not travel internationally, you and your family could come into contact with travelers anywhere in your community. When people don’t receive all of the recommended vaccinations and are exposed to a disease, they can become seriously sick and spread it through their community.
In fact, this is exactly what happened with the large, multi-state measles outbreak in 2015 that started in Disneyland. Measles is still common in many parts of the world including some countries in Europe, Asia, the Pacific and Africa. Even in the U.S., we experienced a record number of measles cases in 2014 – 667 people in 27 states. The 2015 Disneyland outbreak likely started from a traveler who became infected with measles when traveling overseas, and then, while still infectious, visited Disneyland. The majority of people in 188 people in 24 states and Washington DC who ended up getting sick with measles were unvaccinated.
In 2018, travelers with measles continue to bring the disease into the U.S. causing outbreaks in communities where groups of people are unvaccinated. Only the fact that most people in the U.S. are vaccinated against measles prevented these clusters of cases from becoming serious epidemics. Learn more about measles outbreaks from the CDC.
The only vaccine-preventable disease that is completely eradicated (gone) from the world is smallpox. Polio is close to being eliminated, but still exists in several countries.This is why we must keep vaccinating for diseases that we don’t see in the U.S. anymore. We must keep these diseases away.
All vaccine-preventable diseases are not the same. Some diseases are more deadly than others, while others are more contagious. But whether the chance of getting sick or dying from is a particular disease is 1 in 100 or 1 in 10,000, you must decide if the risk is worth taking with your family’s and neighbors’ health. No one ever thinks that their child will be the 1 in 10,000 that will die from a vaccine-preventable disease.
How can I evaluate medical research and health information online?
Every day medical and scientific research is reported on by the media and promoted online. However, it can often be confusing to read and to understand. Most researchers write their studies in the language of science and if you don’t have a good working knowledge of that particular medical or scientific field, you may find the concepts and terms very confusing. Additionally, you must keep in mind that just because the medical or scientific study was reported on by the media, or promoted through a person’s or organization’s website or social media page, it doesn’t make it a good, credible or “valid” study.
Digging down into the study and asking some very critical questions about it can help you evaluate the research that was done, and better understand it. The next time you read a medical study, think about:
Who paid for the study/research?
A lot can be understood by knowing who paid to have the study done. For example, a 1998 research paper by Andrew Wakefield was published in the medical journal, The Lancet. This journal article first mentioned the theory, which is now discredited, that colitis and autism spectrum disorders “could” be caused by the MMR (measles, mumps and rubella) vaccine. The worldwide media ran with the story and as a result immunization rates for MMR dropped; the number of people sick and/or hospitalized from measles, mumps and rubella increased; and a number of deaths from measles occurred. Yet, no one looked at who paid Wakefield to do his research study until February 2004 when a reporter named Brian Deer wrote an article that was published in The Sunday Times of London. Deer investigated Wakefield and others related to the study, and found that prior to submitting his research paper to The Lancet, Wakefield received a payment of £55,000 from Legal Aid Board solicitors (lawyers) who were seeking evidence to use against vaccine manufacturers. Deer further revealed that several of the parents that Wakefield quoted in his study as saying that MMR had damaged their children were part of the group of litigants (accusers) in the legal case. As a result of Deer’s research into Wakefield and his study, The Lancet officially retracted Wakefield’s published study and Wakefield eventually lost his medical license.
Did the researcher study animals or people?
Not all animal studies of medical or treatment interventions (e.g., medication, vaccine, etc.) show exactly what will happen when the same intervention or treatment is tested in humans. There are differences in animals and humans – in physiology, anatomy and other factors. This means that the best a researcher can do after reviewing the results of animal studies is to recommend whether or not a human study could be/should be successfully conducted. Until a human study is done, a researcher cannot be sure that the same results of the animal studies will be achieved.
Who are the people (subjects) that were observed in the study?
Sometimes a very specific group or “class” of individuals is being studied (e.g., men with diabetes; children living in urban areas; etc.) and you need to know that. When a researcher narrows his focus to a specific class of individuals, it limits how broadly the conclusions of the study can be applied to the general population. While the research may be important, the study’s results may be very limited.
Was the study a randomized controlled trial?
A randomized controlled trial is when the people participating in the study (subjects) are randomly divided into separate groups, so the researcher can compare different medical treatments or interventions. By randomly dividing the study’s subjects into different groups, it means that the groups will be similar and that the effects of the medical treatment/intervention they receive can be compared more fairly. When the researcher starts his randomized controlled trial, he should not know which medical treatment/intervention will work best.
Where was the research done?
This may seem like a matter of little importance, but there is a growing body of evidence that says that the physical setting of a study, can greatly influence study’s results.
Were there side effects?
If a researcher is conducting a study of a medical intervention or treatment, it is important to note how he monitored for side effects and what those side effects were. All potential side effects should be noted during a study, and then it is important for the researcher to dig down into the data and determine whether or not each adverse event is actually caused by the medical intervention/treatment. Just because a researcher observes an adverse event after the study subject(s) received the medical intervention, it does not necessarily mean that the medical intervention caused that adverse event or side effect. In other words, just because two events happen at the same time, it doesn’t mean that one caused the other.
Who is reporting the results and through what publication(s)?
Both the researcher who conducted the study and the location where the study is published (e.g., website, medical journal, etc.) should be trusted. You should find out – Is the researcher known for doing quality research? Has his or her research ever been discredited or identified as a “weak” study? Is the publisher known for publishing peer-reviewed studies? A peer-reviewed study is one where “peers” of the researcher who are qualified members of the profession within the relevant field and of similar competence to the author review the work so that standards of quality are maintained and credibility of the research is provided.
How do I know if a study is considered good science or bad science?
Good Science vs. Bad Science
In order for science to be considered “good”, it must follow certain rules and guidelines. These rules and guidelines are a formal process known as the “Scientific Method”. To conduct good science using the scientific method, the researcher must:
- Ask a question
- Do some research to find out what, if anything, is already known about the question or topic. If a person is researching a medical or scientific topic, he/she should make sure to look at credible, science-based sources of information.
- Develop a “testable” hypothesis. A hypothesis is a proposed explanation or theory made on the basis of limited evidence as a starting point for further study. Sometimes people refer to the hypothesis as “an educated guess”.
- Do an experiment or study to determine whether the hypothesis is right (true) or not (false).
- Analyze the data from the experiment/study and draw a conclusion regarding the hypothesis that was tested.
- If the study shows that the hypothesis is false, the researcher should decide if he needs to create a new hypothesis.
- If the study shows that the hypothesis is true, the researcher should communicate his study’s results to others.
There are many steps to testing a hypothesis and then communicating the results from a study, and there are many pitfalls along that road. The first pitfall comes from our very nature as humans and the fact that science is a human endeavor. For example, in a researcher’s eagerness to prove or disprove his study’s hypothesis (usually something he is passionate about), he may accidentally skip a step or two. For example, a researcher may:
- Discredit or overemphasize an observation from his study
- Take shortcuts instead of using proper study methods
- Create a weak test of his hypothesis (theory)
- Include opinions into his study observations and treat them as “facts”
- Start with a conclusion instead of a hypothesis (theory), and then design a “study” to prove his conclusion
Seeing the list of the possible mistakes that a researcher can make, shows why one of the most important parts of good science is to publish the study. If the study is not published, then other researchers/scientists can’t try to reproduce it and make sure that the original study’s conclusions are valid. And in good science, if others cannot reliably duplicate the study’s findings using the same study methods, then there is reason to doubt that the study’s results are valid.
The good scientist is also their own greatest critic. For example, American physicist Richard Feynman (1918-1988) is known for saying, “…if you’re doing an experiment, you should report everything that you think might make it invalid — not only what you think is right about it; other causes that could possibly explain your results; and things you thought of that you’ve eliminated by some other experiment, and how they worked — to make sure the other fellow can tell they have been eliminated.”
When communicating the results from a study or discussing a theory, a good researcher should also share any information that could cause doubt about his study’s theory and/or results. For example, if a researcher shares his study’s results with others, he should also mention all the facts that disagree with his theory/study results, as well as the facts that agree with it. Overall, the idea is to try to give all the information available to help others judge the value of your research; not just the information that leads people to agree with your study’s results.