Epidemics and Outbreaks of Vaccine-Preventable Diseases

Parents usually understand the importance of getting all of the recommended childhood vaccines.

Joe Raedle / Getty Images

Vaccines have done such a good job of controlling diseases in developed countries, such as the United States, that parents sometimes forget just how important they are and what life would be like without them. Current vaccines and past vaccination programs have now controlled over 10 major infectious diseases. Unfortunately, we aren't all living in a post-vaccine era.

Vaccine-Preventable Diseases in the Post-Vaccine Era

Except for smallpox, many diseases that have been largely eradicated in the developed world are still rampant in third world and developing countries. This means those diseases could make a comeback anywhere. Worldwide, the World Health Organization (WHO) reports continued outbreaks of many vaccine-preventable illnesses, including:

  • Diphtheria: 4,489 cases and 2,500 deaths (2011)
  • Haemophilus influenzae type b: 199,000 deaths (2008)
  • Measles: Over 140,000 deaths (2018)
  • Mumps: Over 680,000 cases in children and adults (2012)
  • Neonatal tetanus: 59,000 deaths (2008)
  • Pertussis: 195,000 deaths (2008)
  • Pneumococcal disease: 476,000 deaths (2008)
  • Poliomyelitis: 404 cases in 2013
  • Rotavirus: 453,000 deaths (2008)
  • Rubella: Over 94,000 cases (2012)
  • Tetanus: 63,000 deaths (2008)
  • Yellow fever: 130,000 cases and 44,000 deaths (2013)

Still, there is progress; WHO estimates that worldwide, an estimated 23.2 million deaths were prevented by measles vaccination from 2000 to 2018, and polio is close to eradication. Polio is now endemic in just two countries—Afghanistan and Pakistan.

The Statistics

Epidemics of diseases that are now vaccine-preventable were once very common. For example, epidemics of measles once occurred in regular two- to five-year cycles in the United States, affecting 200,000 to 500,000 people each time.

Although measles has been mostly eradicated in the United States, outbreaks happen when cases are imported from other parts of the globe. Measles remains a leading cause of death of young children around the world.

That is how the early 2008 California measles outbreak began. An unvaccinated child who traveled outside of the country was exposed to measles, got sick, and infected many other children upon returning to California.

Just how quickly these infections can spread is highlighted by other outbreaks and epidemics:

  • Rates of diphtheria, pertussis, and measles greatly increased after the breakup of the Soviet Union as vaccines became less available in Russia and the other newly independent states. Diphtheria reached epidemic levels by 1995 and caused over 4,000 deaths.
  • A 2000 outbreak of measles in Ireland occurred after routine use of the measles, mumps, rubella (MMR) vaccine fell because of vaccine safety fears, leading to 1407 cases and hospital admissions of 111 children. Thirteen of the children were admitted to the intensive care unit, seven were on mechanical ventilators, and three children died.
  • The rate of measles in Europe rose to 30,000 in 2011, leading to eight deaths, 27 cases of measles encephalitis, and 1,482 cases of pneumonia. Most cases were in unvaccinated (82%) or incompletely vaccinated (13%) people, after decreased use of the MMR vaccine.
  • Measles broke out in the Netherlands in 1999 and 2000 among a mostly unvaccinated community. The outbreak resulted in 3,292 cases of measles, 72 hospitalizations, and 3 deaths.
  • In Japan in 2013, there were 14,357 cases of rubella and up to 40 cases of congenital rubella syndrome.


The COVID-19 pandemic has, of course, had devastating consequences around the world. This disease is caused by SARS-CoV-2, a type of coronavirus. More than 92 million cases of COVID-19 have been documented in the United States as of November 30, 2022. Roughly 15 million cases (or 18% of the U.S. total) occurred in people under the age of 18.

Children under the age of 5 appear to be at lower risk of contracting the virus than older people, but all ages are susceptible to COVID-19. The U.S. Centers for Disease Control and Prevention (CDC) recommends that everyone get the COVID-19 vaccine and any recommended boosters to protect themselves, their families, and their communities. Everyone ages 5 and up is eligible for a booster, and so are some kids under 5.

All unvaccinated people should take precautions to stop the spread of COVID-19:

  • Avoid crowds and poorly ventilated areas.
  • Stay six feet away from other people.
  • Wash hands often, before eating, and after blowing your nose.
  • Wear a face mask.


Diphtheria is a vaccine-preventable illness that is caused by the Corynebacterium diphtheriae bacteria. Symptoms can include a fever, sore throat, and runny nose, and can resemble a common cold.

The diphtheria bacteria can produce a toxin that can cause a thick white membrane, which can bleed, to form on an infected person's throat. They can also develop a "bull neck" appearance because the glands in the neck became so enlarged. It's like strep throat on steroids, and is definitely not something you want your kids to get.

Complications from diphtheria include myocarditis (inflammation of the heart), airway obstruction, coma, and death. Five percent to 10% of unvaccinated people with diphtheria die.

Although there are now few cases of diphtheria in the United States, before routine vaccination with the diphtheria vaccine (the D in the DTaP vaccine), which began in the 1920s, there were more than 125,000 cases and 10,000 deaths each year.

Haemophilus influenzae Type B

People often confuse this bacterial infection with the flu, but it actually has nothing to do with influenza except for the fact that it was first discovered during a flu epidemic.

Haemophilus influenzae type b (Hib), before the routine use of the Hib vaccine, was the common cause of bacterial meningitis. It also often caused bacteremia (a blood infection), pneumonia, and endocarditis (an infection of the valves of the heart). 

Hib can also cause bacterial infections in other parts of the body, including cellulitis (skin infections), suppurative arthritis (joint infections), and osteomyelitis (bone infections).

Epiglottitis, another infection that can be caused by the Hib bacteria, is a medical emergency. Affected kids needed very quick treatment for a chance to survive.

Before the routine use of the Hib vaccine began in 1988, about 20,000 children had Hib infections each year, including 12,000 cases of bacterial meningitis. Complications from meningitis could be severe, affecting about 30% of kids, and included deafness, seizures, blindness, and cognitive impairments. About 5% of children with bacterial meningitis that was caused by the Hib bacteria died.


Measles is an extremely contagious viral infection. Before routine measles immunization began in the United States began in 1963, there were about 4 million cases of measles each year.

Unfortunately, about 20% of the children who had measles had complications, including ear infections (10%), pneumonia (5%), and measles encephalitis (0.1% or 1 in 1,000). Encephalitis is an inflammation of the brain that can lead to seizures, deafness, and brain damage.

Most importantly, about one to three of every 1,000 cases of measles results in death.

Because it is extremely contagious, it's still a problem in many parts of the world. Some parents still worry about the MMR vaccine, even though overwhelming scientific evidence says it is safe. Consequently, health experts are on guard for a measles comeback if immunization rates drop.


Mumps is a form of parotitis (inflammation of the parotid gland) that is caused by the paramyxovirus. Complications can include meningitis, encephalitis, orchitis (inflammation of the ovaries or testicles), pancreatitis, and myocarditis.

Except for an occasional outbreak, mumps is now rare in the United States. The mumps vaccine was introduced in 1968 and began to be used more routinely in 1977 (it is the middle M in the MMR vaccine). Outbreaks still occur periodically in other countries.


Pertussis, or whooping cough, is caused by the Bordetella pertussis bacteria. Although it is now associated with causing an annoying, lingering cough in teens and adults, it is important to remember that pertussis used to be one of the leading causes of death from infections for children.

Before routine use of the pertussis vaccine in the 1940s, about one out of every 750 children in the United States died from pertussis each year.

Complications of pertussis infections include seizures, pneumonia, apnea, encephalopathy (altered mental status). Up to 1% of infected infants die from pertussis.

Unlike most of the other vaccine-preventable illnesses, there continue to be about 5,000 to 7,000 cases of pertussis each year in the United States. This is mostly because immunity from childhood pertussis vaccines (the aP in DTaP vaccine) wears off after 5 to 10 years.

This means that teens and adults can get pertussis and pass it on to infants who haven't had the vaccine yet. Following the recommendation for a booster dose (Tdap) at age 12 helps to combat these pertussis infections.


Although some people think that polio has already been eradicated, there were over 400 cases of polio around the world in 2020. Most cases are now concentrated in just a few countries, including Afghanistan and Pakistan, where it is still endemic.

Before the polio vaccine came into use in 1955, polio outbreaks were common in the United States. Polio is caused by a virus and although many children who become infected don't develop any symptoms, about one in 200 who are infected develop paralytic polio. Many of these children have a permanent disability, and 5% to 10% do not survive.

During regular outbreaks in the United States, there were up to 21,000 cases of paralytic polio each year. Parents feared polio so much that swimming pools and playgrounds were closed during summers when there were epidemics.

Mass immunization campaigns in the few remaining countries where polio is a problem and continued immunization in all other parts of the world means that the goal of eradicating polio is in reach.


Rubella is also known as German measles or "three-day measles." Unlike most of the other vaccine-preventable infections, this viral disease is usually mild. In fact, many people with rubella don't have any symptoms. The rest have lymphadenopathy (swollen glands), a rash, and low-grade fever that typically lasts for three days.

If rubella is so mild, why do we need a vaccine for it? The main reason is that pregnant women who contract rubella in their first trimester are at increased risk of miscarriage. Up to 80% of babies born to mothers with rubella develop congenital rubella syndrome.

These babies are often born with severe birth defects including cataracts, deafness, glaucoma, heart defects, hepatitis, low birth weight, cognitive deficits, microcephaly (a small head), and thrombocytopenic purpura (low blood platelet counts).

During a rubella outbreak from 1964 to 1965, there were about 20,000 cases of congenital rubella syndrome. Rubella is now rare in the United States since the introduction of the rubella vaccine in 1969 (it is a part of the MMR vaccine). But since rubella has not been eradicated, continued vaccination is important.


Most parents associate tetanus with "lockjaw" and needing a tetanus shot if you step on a rusty nail. The tetanus vaccine was introduced in 1938.

Tetanus is caused by toxins produced by the Clostridium tetani bacteria. Spores of the C. tetani bacteria are commonly found in soil and in the intestines of many animals. The spores can easily contaminate cuts, scrapes, and other wounds — especially dirty wounds.

Unlike all other vaccine-preventable illnesses, tetanus is not contagious. Good hygiene and continued vaccination with the tetanus vaccine (the T in the DTaP and Tdap vaccines) have led to low levels of tetanus in the United States. It is still a major problem in other parts of the world.

Other Vaccine-Preventable Illnesses

These major infections have been conquered or are well controlled in the United States by vaccines. Health experts are still working on eliminating others with new vaccines.

Some viruses and bacteria mutate over time or include multiple strains. Current vaccines help, but haven't eliminated the diseases entirely.

This includes seasonal influenza, and is why a new flu vaccine must be given each year. The pneumococcal, meningococcal, and rotavirus vaccines only target certain strains of bacteria and viruses. The chickenpox, hepatitis B, and hepatitis A vaccines haven't been given to enough people to eliminate these infections.

COVID-19 is another example of a vaccine that may change each year to address the most current variants. Researchers are still discovering new properties of this virus and developing the most effective vaccines to combat it.

  • Chickenpox: Although many parents think chickenpox is a mild infection, before the routine use of the chickenpox vaccine began in 1995, there were about 4 million cases of chickenpox each year, with an average of 10,500 hospitalizations and 100 deaths.
  • Flu: Even though a yearly flu vaccine is recommended for all children who are at least six months old, there continue to be flu deaths among children every year (199 children died from flu in the 2019-2020 flu season).
  • Hepatitis A: Unlike hepatitis B, children usually get hepatitis A from daycare and from eating contaminated food, including seafood, fresh produce, and from outbreaks in restaurants. Most children in developing countries become infected with the hepatitis A virus, and although usually not fatal, it is one of the most common vaccine-preventable illnesses in the United States too.
  • Hepatitis B: About 400 million in the world are chronically infected with the hepatitis B virus, including over 1 million people in the United States. Children can get hepatitis B from blood and body fluids and if they are born to a mother with it, which is why it is important that they get their first hepatitis B vaccine as soon as possible. Universal infant vaccination has greatly reduced the cases of childhood hepatitis B infections.
  • Pneumococcus: Streptococcus pneumoniae can cause meningitis, pneumonia, bacteremia, and ear infections. Two pneumococcal vaccines, including Prevnar that is given with routine childhood immunizations, and Pneumovax, given to older high-risk children and adults, is helping to decrease these infections. Before the vaccines were available, S. pneumoniae caused about 700 cases of bacterial meningitis and 200 deaths each year in children. Worldwide, it is thought to cause about 1.9 million deaths each year in children under age 2.
  • Meningococcus: Neisseria meningitides leads to over 50,000 deaths each year around the world. In the United States, there are about 2,000 to 3,500 cases each year, and about 10% of affected children die. The Menactra and Menveo meningococcal vaccines are recommended for all children when they are 11 to 12 years old.
  • Rotavirus: Worldwide, there are about 450,000 to 600,000 deaths in children each year from rotavirus, a common cause of diarrhea. In the United States, rotavirus causes about 3 million cases of diarrhea, which leads to about 80,000 hospitalizations, and 20 to 40 deaths, although this is greatly decreasing now that we have two rotavirus vaccines — RotaTeq and Rotarix.

Unfortunately, there are many childhood infections for which there are no vaccines yet, like malaria (over 600,000 deaths each year), tuberculosis (1.5 million deaths each year), and HIV/AIDS (over 680,000 deaths each year).

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Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Vincent Iannelli, MD
Vincent Iannelli, MD, is a board-certified pediatrician and fellow of the American Academy of Pediatrics. Dr. Iannelli has cared for children for more than 20 years.