Vaccines help everyone — even the unvaccinated | Science News for Students

Vaccines help everyone — even the unvaccinated

Here’s why falling vaccination rates worry doctors, cancer patients and parents of young babies
Apr 4, 2019 — 6:45 am EST
a group of middle school students running towards the viewer

Most people think that vaccines only help those who get that shot in their arm. In fact, vaccines also limit the spread of disease to people who, for medical reasons, cannot be vaccinated.

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Kids’ cuts and scrapes are rarely a big deal. But one six-year-old boy in Oregon nearly died after getting a cut on his forehead while playing outside. Six days after the accident, his jaw began clenching. Muscle spasms wrenched his arms. His neck and back arched out of control. Then the boy had trouble breathing. Emergency medical personnel airlifted the child from the family farm to a hospital. Doctors quickly figured out the problem: tetanus.

The bacteria that cause tetanus are everywhere, notes the Centers for Disease Control and Prevention (CDC) in Atlanta, Ga. Luckily, there’s a vaccine that can prevent tetanus. But the boy’s parents wouldn’t let him get it.

As a result, the child became so sick he had to spend 57 days in a hospital. For more than a month of that time, he needed a breathing machine. After the hospital, he had to spend 17 more days in a health-recovery center. The treatment was costly: $811,929. And that didn’t cover the cost of airlifting him to the hospital when his symptoms turned deadly.

Eventually, the boy got better. Yet even after doctors explained the tiny risks and huge benefits of vaccines, his parents refused follow-up doses of vaccine for their son.

U.S. Reported tetanus cases have dropped dramatically over time
This graph shows the success of the tetanus vaccine, over time, in reducing U.S. incidence of that life-threatening disease.
CDC

Doctors described his case in the March 8 issue of Morbidity and Mortality Weekly Report (MMWR).

“Vaccines are safe. Vaccines save lives,” says Peter Hotez. “They are the most effective public health technology ever invented.” He’s a pediatrician and vaccine scientist at Baylor College of Medicine and Texas Children’s Hospital. Both are in Houston.

Most people gladly get vaccines for themselves and their children. Yet a small share of people says no. In fact, the percent that turns them down has been climbing. That is putting more children at risk. And it endangers the health of others, from babies to cancer patients and more.

“We’ve reached a point where so many children are not being vaccinated, that we’re seeing a return of dangerous and even deadly infectious disease,” Hotez says.

Protection from disease

Vaccines work by arming the immune system to fight off a disease. “A vaccine gives your body a little sample of what a virus or bacterium looks like,” explains Danielle Koenig. She’s a health educator with the Washington Department of Health in Olympia. A vaccine prompts the immune system to make germ-killing antibodies. Later, if you’re exposed to those germs, “your body has those antibodies ready to go.”

But that’s not all. Many vaccines help protect other people from infections. As more and more people get a vaccine, the disease has fewer people it can infect. And that’s the first step in slowing or even stopping its spread. Public health experts call this herd immunity

Herd immunity works like a shield or force field to protect those people who are most at risk because they cannot be vaccinated, Koenig says. “The more people who get vaccinated, the stronger that field is.” On the flip side, “if not enough people are immunized, that force field breaks down and there are holes in it.”


Herd Immunity:

a gif showing how infectious disease spreads in various scenarios
1: For highly infectious diseases, such as measles, sickened people (shown in red) can quickly spread the disease through a large share (right) of the exposed population.
2: When few people are vaccinated (shown in yellow, left), a highly contagious disease can still quickly spread (red, at right) to unvaccinated people.
3: When most people get a vaccine (yellow, at left), they greatly limit how effectively an infection can spread (red, at right) within a population. Their ability to protect others is known as “herd immunity.”
Tkarcher/Wikimedia Commons (CC BY-SA 4.0)

Measles is a disease that causes high fevers, coughing, a sore throat and an ugly rash. One or two in every 1,000 people who get measles will die from it, the CDC notes. Many more will end up with pneumonia, brain infections and nervous-system damage, such as deafness. Measles also makes it hard to fight off certain other diseases for the next two to three years.

“Measles is a very dangerous disease,” observes Jonathan McCullers. He is a pediatrician at the University of Tennessee Health Science Center and Le Bonheur Children’s Medical Center in Memphis. He’s also a faculty member at St. Jude’s Children’s Research Hospital in the same city.

In contrast, “the vaccine against measles is very safe and very effective. One dose provides protection in about 93 percent of individuals,” McCullers says. A second, booster dose bumps the protection up to 97 percent. And, he notes, “Very few side effects occur.” 

Herd immunity also protects individuals who can’t be vaccinated. This includes babies who are too young to get vaccines. It also counts cancer patients and others with weak immune systems. About one in eight U.S. children and teens depend on herd immunity to protect them from measles. This also includes about 3 in every 100 people for whom a vaccine might not offer full protection. And it counts children whose parents say no to vaccines. These people can still become infected. But they’re far less likely to get sick because of herd immunity.

a nurse preparing a measles vaccine
This nurse in Ethiopia is preparing a shot of measles vaccine for her patient.
Pete Lewis/DFID/United Kingdom Department for International Development/Flickr (CC BY 2.0)

Measles is only one of many diseases for which there is a vaccine. Another is pertussis (Pur-TUSS-is), which triggers a severe hacking cough. (In babies it is known as whooping cough, for the sound of their coughs.) This infection can cause pneumonia, convulsions, brain disease and breathing problems.

A tetanus vaccine could have prevented the disease that almost killed the Oregon boy. Other diseases that a vaccine could prevent: diphtheria (Dip-THEER-ee-uh), which makes it hard to breathe and can lead to heart failure. There’s also rotavirus, which causes severe and sometimes deadly diarrhea. Vaccinations can prevent chickenpox, which produces fever, a rash and sometimes serious nerve damage in later life (known as shingles). Vaccinations can also prevent Rubella (Rue-BEL-lah), which can trigger fetal deaths in pregnant women.

And then there’s the yearly vaccine against flu. This common infection kills tens of thousands of people in the United States each year. Teens also need vaccines for human papillomavirus (Paa-pil-LOH-muh-vy-rus) and meningococcal (Meh-NIN-jo-KOK-ul) disease. The first of these can lead to cancer. The second attacks the nervous system and blood stream.


Diseases most people don’t have to get, now, thanks to vaccines:
a microscopic image of the Clostridium tetani bacteria an illustration of a measles virus

a microscopic image of Corynebacterium diphtheriae bacterium

a digitally-colorized transmission electron microscopic image of rotavirus

transmission electron microscopic (TEM) image of the Varicella zoster virus

an illustration of a human papillomavirus

A growing problem

On March 5, 18-year-old Ethan Lindenberger of Norwalk, Ohio, spoke to lawmakers in Washington, D.C. The high school student spoke of how his mother wouldn’t let him get vaccines when he was little. As a teen, he learned about the science behind vaccines. He talked with his mom, but she still said no. When he turned 18, Ohio law said he no longer needed his parents’ okay. So Ethan finally got those vaccines. But for 18 years he was at risk.

Lindenberger didn’t get measles as a child. He also didn’t get other infections that vaccines could prevent. And he credits herd immunity for that. “The people around me were vaccinated,” he tells Science News for Students. “Other people’s concern for safety was keeping me safe.”

Ethan Lindenberger testifies at a March 5, 2019 hearing, in Washington, D.C., convened by the U.S. Senate’s Committee on Health, Education, Labor and Pensions. The teen describes growing up unvaccinated.
PBS NewsHour/YouTube

In turn, Ethan felt concern for others. So when he was legally able to, he got vaccinated. “I saw that getting vaccines not only protects yourself but other people, and that was a big thing for me,” he says.

Before a measles vaccine became available in 1963, there were nearly half a million U.S. cases each year, of which nearly 500 died, the CDC says. Thanks to vaccines, though, the United States eliminated measles in 2000. And since 2000, the vaccine has prevented more than 21 million deaths worldwide, according to a November 30, 2018 report in MMWR.

However, unvaccinated travelers can still bring the airborne virus into the country from places where the disease is common. Already in 2019, New York, Texas, Illinois, Michigan, Oregon and Washington have been fighting outbreaks. As of March, most patients in the Washington outbreak had never been vaccinated for measles.

Since 2011, CDC reports there have been more than 2,100 cases of measles — 268 so far this year. Outbreaks happen elsewhere, too. Europe had more than 82,000 cases in 2018. Brazil had more than 10,000 cases that year. Those data come from the World Health Organization and the Pan American Health Organization.

a cute baby swathed in blankets and lying on a bed next to a blue card
The blue card shows that this baby in Yemen is now protected from several diseases. Vaccine schedules for babies depend on several factors, including when their mom’s immunity to a disease is likely to wear off.
Julien Harneis/Flickr (CC BY-SA 2.0)

Vaccine-preventable diseases should be on the decline. However, that is no longer true for some of these diseases. That’s because not everyone who can be vaccinated gets their recommended vaccines. As of 2017, about 13 in every 1,000 children under age two had never gotten a vaccine. That’s more than four times as many as in 2001, the CDC reported last year.

That 13 in every 1,000 may sound like a tiny number. But 3.86 million babies were born in the United States in 2017. So if the rate stays the same, that’s more than 50,000 more unvaccinated kids each year.

All U.S. states have laws that say children must get certain vaccines to attend school or daycare. A small share of those kids can’t get vaccines for medical reasons. And the laws allow for that. But the vast majority who don’t get vaccines have no medical exemption. As of 2018, 47 states allowed parents to say no for religious reasons. And laws in 18 states now let parents say no based on just their personal beliefs.

Saad Omer is an epidemiologist — a disease detective — at Emory University’s Vaccine Center in Atlanta, Ga. For a 2016 study, he led a team that reviewed 18 reports on measles outbreaks. More than half the people who were infected had never gotten the measles vaccine. And seven in every 10 of these people had no medical reason. That shows that vaccine refusals play a role in causing and spreading measles, the team concluded. Omer talked about his team’s findings at the same hearing where Ethan spoke.

Herds at risk

Herd immunity only works if enough people in a group have had their vaccines. The exact number depends on how fast a disease spreads and other factors. Measles is very contagious and spreads through the air. On average, Hotez explains, for every one person who gets measles, 12 to 18 more will now get it, too — “if they’re not vaccinated.” Measles outbreaks show up first when people skip vaccines, he says.

a photo of a happy vaccinated girl
Getting vaccination shots can pinch for a moment. But this shot in the arm can protect you — and often others — from some very nasty diseases.
Pornpak Khunatorn/iStock/Getty Images Plus

So public health officials aim for a 92 to 95 percent vaccination rate.

Some places are near or already below that threshold. In 2018, the rate for measles vaccination in Arkansas was just under 92 percent. This and other states also have “pockets” where clusters of vaccine-refusers live, says McCullers.

Even if a state’s overall rate is high, those clusters may be below the levels needed for local herd protection. Outbreaks can then spread easily there. And from there, they can “spill out into other populations,” McCullers says. That poses a big problem for children and other people who have no protection.

Arkansas isn’t the only place with areas like that. In a 2018 study, Hotez and others identified U.S. “hot spot” counties, ones with the most nonmedical refusals. Parents of more than one in every 20 children in those places had said no to their getting vaccines.

“We found more than 100 hot spots like that in the country,” Hotez says. Rural Camas County, Idaho, had the highest rate (nearly 27 percent unvaccinated) — or more than one in every four kids. The list also has several urban counties with recent measles outbreaks. They include counties around or near Portland, Ore., Detroit, Mich., and the Texas metro areas of Houston, Fort Worth and Plano. His team identified those hot spots last June in PLOS Medicine.

a map showing rates of occurences of unvaccinated children in states that allow parents to withhold vaccinations for nonmedical reasons
This map shows rates in the 18 U.S. states that as of 2016 allowed parents to withhold vaccinations from their children for nonmedical reasons. Deep red areas had the highest rate of such exemptions — between 5 and 30 percent. 
J.K. Olive et al/PLOS Medicine, 2018

It doesn’t take a big drop to cause problems, either. Hotez and a colleague found that just a 5 percent drop in vaccination rates could triple the number of measles cases each year for U.S. children aged two to 11. And the public health costs of dealing with those cases would be an extra $2.1 million per year. Hotez and Nathan Lo reported those findings in the September 2017 JAMA Pediatrics.

What can be done?

In a sense, vaccines are victims of their own success, Ethan notes.

McCullers agrees. “If they work really well, nobody sees the disease for 30 years, and you get really complacent,” he says. But when a disease reemerges, people see the awful impacts. The little boy in Oregon was just “a regular kid who scrapes his forehead,” McCullers says. “Then he’s in the hospital for months with this horrible and painful disease.”

a vial containing an experimental Zika vaccine
Zika is one of the most recent highly infectious viral diseases for which a vaccine is being developed.
National Institute of Allergy and Infectious Diseases, National Institutes of Health/Flickr (CC BY-NC 2.0)

More education for parents may help avoid such problems. Starting in 2011, Washington state law has made parents get counseling from a licensed healthcare provider before they can refuse vaccines for their children. Vaccination rates went up for all but one available vaccine once the law was in effect. Omer and others reported that news last year in Pediatrics.

Policy makers can take action, too. As of March 2019, Oregon lawmakers are considering a bill to end non-medical exemptions from required vaccines. Another idea might be for lawmakers to lower the age when teens can get vaccines on their own. In most states that’s now age 18. However, some states let “mature minors” give their own consent.

What if you need your parents’ permission to get vaccines? Talk with your pediatrician or family doctor, Hotez suggests. Ask about your options. Your doctor may help talk to your parents as well.

“Be respectful, and be as kind as you can be,” when you talk with a parent or guardian, Ethan advises kids and teens. Although he says his mom was wrong about vaccines, he knows she loves him. So he keeps sharing the facts with her. He hopes his four younger siblings will eventually decide to get their vaccines.

Most people who reject vaccines “are coming from a fear-based, emotional place,” says Koenig at the Washington State Department of Health. “We suggest appealing to their brain and their heart. Understand where they’re coming from, and acknowledge that they want the best for their family.” Then try to address those feelings, she says, while staying true to the science.

If someone worries about side effects, for instance, focus on what any real side effects are — instead of ones spread through misinformation. Then you can talk about the much greater dangers of getting a preventable disease. Or, if someone thinks vaccines are gross, talk about how disgusting disease impacts can be. Those suggestions come from Matthew Motta. He’s a political scientist at the University of Pennsylvania in Philadelphia. He studies science communication and public policy impacts when people reject science.

Promote sound science about vaccines on social media too, suggests McCullers. Just as teens used social media to spread the word about school strikes for climate action, young people can speak out about the importance of vaccines, he says. “Now one teen has one voice, and that voice can go around the world.” (And yes, you can link to this article!)

Share personal stories and concerns as well, McCullers says. Think about the people you care about, and speak up for them. Maybe you have a baby brother, sister or cousin who could be in danger from unvaccinated people. Perhaps you don’t want your grandparents to face more risks from flu or other illnesses. You might also have a friend or family member whose immune system is weak because of cancer or another disease.

Full disclosure: My daughter Bethany died from cancer in 2018. Treatments weakened her immune system. So an infectious disease could have made her sicker or killed her. I echo what her husband Jarrod wrote on Facebook: “I got an extra two-and-a-half years with Bethany because everyone who loved her listened to our requests and was vaccinated against diseases that are easily dealt with.”

Power Words

(more about Power Words)

antibody     Any of a large number of proteins that the body produces from B cells and releases into the blood supply as part of its immune response. The production of antibodies is triggered when the body encounters an antigen, some foreign material. Antibodies then lock onto antigens as a first step in disabling the germs or other foreign substances that were the source of those antigens. 

autism     (also known as autism spectrum disorders ) A set of developmental disorders that interfere with how certain parts of the brain develop. Affected regions of the brain control how people behave, interact and communicate with others and the world around them. Autism disorders can range from very mild to very severe. And even a fairly mild form can limit an individual’s ability to interact socially or communicate effectively.

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

bacteria     (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.

cancer     Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

Centers for Disease Control and Prevention, or CDC     An agency of the U.S. Department of Health and Human Services that is charged with protecting public health and safety by working to control and prevent disease, injury and disabilities. CDC does this by investigating disease outbreaks, tracking exposures by Americans to infections and toxic chemicals, and regularly surveying diet and other habits among a representative cross-section of all Americans.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

colleague     Someone who works with another; a co-worker or team member.

complacent     To be smug or uncritical about one's skills or achievements, or to be unduly assured that some pleasant conditions will continue on unchanged. 

contagious     An adjective for some disease that can be spread by direct contact with an infected individual or the germs that they shed into the air, their clothes or their environment. Such diseases are referred to as contagious.

diarrhea     (adj. diarrheal) Loose, watery stool (feces) that can be a symptom of many types of microbial infections affecting the gut.

diphtheria      A bacterial infection where the germs produce a poison that destroys healthy tissue in the respiratory system. Within a few days, it can become hard to breathe. Other symptoms include weakness, fever and a very sore throat. If the poison enters the bloodstream it can eventually damage the heart, kidneys and nerves. There is a vaccine to prevent the disease. It is usually administered to children as part of a cocktail of vaccines that also target tetanus and pertussis (whooping cough).

epidemiologist     Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

factor     Something that plays a role in a particular condition or event; a contributor.

flu     Short for influenza, a highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.

germ     Any one-celled microorganism, such as a bacterium or fungal species, or a virus particle. Some germs cause disease. Others can promote the health of more complex organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

heart failure     A weakening of the heart that leads to its inability to pump enough blood to meet the needs of its tissues. It does not mean the heart has stopped. But if left untreated, heart failure can lead to death.

herd immunity     A term that refers to the idea that if most people within a population are immune to a disease, then they can’t spread it. This tends to protect most people who are not immune.

high school     A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.

immune     (adj.) Having to do with the immunity, the ability to fight infections or deal with foreign substances that may provoke allergies. (v.) Able to ward off a particular infection. Alternatively, this term can be used to mean an organism shows no impacts from exposure to a particular poison or process. More generally, the term may signal that something cannot be hurt by a particular drug, disease or chemical.

immune system     The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

infect     (adj. infectious) To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.

infection     A disease that can spread from one organism to another. It’s usually caused by some type of germ.

link     A connection between two people or things.

mature     (adj.) Connoting an adult individual or full-grown and fully developed (non-juvenile) form of something. (verb) To develop toward — or into — a more complex and  full-grown form of some individual, be it a plant, animal or microbe.

measles     A highly contagious disease, typically striking children. Symptoms include a characteristic rash across the body, headaches, runny nose, and coughing. Some people also develop pinkeye, a swelling of the brain (which can cause brain damage) and pneumonia. Both of the latter two complications can lead to death. Fortunately, since the middle 1960s there has been a vaccine to dramatically cut the risk of infection.

meningococcal disease     A potentially deadly disease caused by infection with Neisseria meningitides bacteria. Spread by saliva, it can be picked up through kissing or sharing a room with someone (such a camp or dorm room). Symptoms can be initially mistaken for flu, including a fever, headache, nausea, vomiting, confusion and stiff neck. If not treated in time, the germs can infect the lining of the brain and spinal cord or bloodstream.

 minors     Children and adolescents below an age that would make them legally adults.

morbidity     The prevalence of illness; the share of people having a particular sickness at some particular time or in some particular place.

mortality     Deaths. From mortal, meaning deadly.

muscle     A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

nervous system     The network of nerve cells and fibers that transmits signals between parts of the body.

outbreak     The sudden emergence of disease in a population of people or animals.

pediatrics     A field of medicine that has to do with children and especially child health. A doctor who works in this field is known as a pediatrician.

pneumonia     A lung disease in which infection by a virus or bacterium causes inflammation and tissue damage. Sometimes the lungs fill with fluid or mucus. Symptoms include fever, chills, cough and trouble breathing.

policy     A plan, stated guidelines or agreed-upon rules of action to apply in certain specific circumstances. For instance, a school could have a policy on when to permit snow days or how many excused absences it would allow a student in a given year.

political scientist     Someone who studies or deals with the governing of people, largely by elected officials and governments. 

population     (in biology) A group of individuals from the same species that lives in the same area.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

rubella     A formerly common childhood infection sometimes called the “German” measles or three-day measles. The short-lived infection tends to cause a slight fever and rash that spreads from the face to the rest of the body. Almost half of infected people show no symptoms. The big risk is to the baby of women who get the disease during pregnancy. The child may develop deafness, vision problems, heart defects, mental retardation and liver or spleen damage.

sibling     An offspring that shares the same parents (with its brother or sister).

side effects     Unintended problems or harm caused by a procedure or treatment.

social media     Internet-based media, such as Facebook, Twitter and Tumblr, that allow people to connect with each other (often anonymously) and to share information.

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

tetanus     An unusual type of bacterial infection that usually does not spread between infected individuals. The source of these germs is typically exposure to soil, dust or animal feces. The disease causes stiff, painful muscles throughout the body, including a cramping in the jaw (which is why it’s sometimes called “lockjaw”). Fevers, seizures, sweating and headaches may also occur.

threshold     A lower limit; or the lowest level at which something occurs.

urban     Of or related to cities, especially densely populated ones or regions where lots of traffic and industrial activity occurs. The development or buildup of urban areas is a phenomenon known as urbanization.

vaccine     (v. vaccinate) A biological mixture that resembles a disease-causing agent. It is given to help the body create immunity to a particular disease. The injections used to administer most vaccines are known as vaccinations.

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.

World Health Organization     An agency of the United Nations, established in 1948, to promote health and to control communicable diseases. It is based in Geneva, Switzerland. The United Nations relies on the WHO for providing international leadership on global health matters. This organization also helps shape the research agenda for health issues and sets standards for pollutants and other things that could pose a risk to health. WHO also regularly reviews data to set policies for maintaining health and a healthy environment.

Citation

Journal: J. Guzman-Cottrill et al. Tetanus in an unvaccinated child — Oregon, 2017. Morbidity and Mortality Weekly Report. Vol. 68, March 8, 2019, p. 231. doi: 10.15585/mmwr.mm6809a3.

Journal: A. Hviid et al. Measles, mumps, rubella vaccination and autism: A nationwide cohort study. Annals of Internal Medicine. March 5, 2019. doi: 10.7326/M18-2101.

Journal: S. Omer and I. Yildirim. Further evidence of MMR vaccine safety: Scientific and communications considerations. Annals of Internal Medicine. March 5, 2019. doi: 10.7326/M19-0596.

Hearing: United States Senate. Committee on Health, Education, Labor and Pensions. “Vaccines Save Lives: What Is Driving Preventable Disease Outbreaks?” Washington, D.C. March 5, 2019.

Hearing: United States House of Representatives. Committee on Energy and Commerce. “Confronting a growing public health threat: Measles outbreaks in the U.S.” Washington, D.C. February 27, 2019.

Journal: A. Dabbagh et al. Progress toward regional measles elimination — worldwide, 2000 – 2017. Morbidity and Mortality Weekly Report. Vol. 67, November 30, 2018, p. 1323. 

Book: P. Hotez. Vaccines Did Not Cause Rachel’s Autism. Johns Hopkins University Press. October 30, 2018. ISBN: 9781421426600.

Journal: H.A. Hill et al. Vaccination coverage among children aged 19 – 35 months — United States, 2017. Morbidity and Mortality Weekly Report. Vol. 67, October 12, 2018, p. 1123. doi: 10.15585/mmwr.mm6740a4.

Journal: J.K. Olive et al. The state of the antivaccine movement in the United States: A focused examination of nonmedical exemptions in states and counties. PLOS Medicine. June 12, 2018. doi: 10.1371/journal.pmed.1002578. Correction. July 6, 2018. doi: 10.1371/journal.pmed.1002616.

Journal: S. Omer et al. Exemptions from mandatory immunization after legally mandated parental counseling. Pediatrics. Vol. 141, January 2018 .

Journal: N.C. Lo and P.J. Hotez. Public health and economic consequences of vaccine hesitancy for measles in the United States. JAMA Pediatrics. Vol. 171, September 2017, p. 887. doi: 10.1001/jamapediatrics.2017.1695.

Journal: R. Bednarczyk et al. Estimating the number of measles-susceptible children and adolescents in the United States using data from the National Immunization Survey–Teen (NIS-Teen). American Journal of Epidemiology. Vol. 184, July 15, 2016, p. 148. doi: 10.1093/aje/kwv320.

Journal: V. Phadke et al. Association between vaccine refusal and vaccine-preventable diseases in the United States. Journal of the American Medical Association. Vol. 315, March 15, 2016, p. 1149. doi:10.1001/jama.2016.1353.

Meeting:  S. Omer. Vaccine refusal and herd immunity for measles. American Association for the Advancement of Science annual meeting, Washington, D.C., February 14, 2016.

Journal: M. Mina et al. Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality. Science, Vol. 348. May 8, 2015, p. 694. doi: 10.1126/science.aaa3662.

Government resource: Centers for Disease Control and Prevention. Tetanus causes and prevention.

Government resource: Centers for Disease Control and Prevention. Measles Cases and Outbreaks.

Further Reading

Video: M. Ferrari. Pennsylvania State University. “Getting measles cases to zero.”