“Herd Immunity” Protects Everyone Against Disease

Under what is called “herd immunity,” when most people in a community are vaccinated against a disease, the virus lacks a host and will eventually go away because there are so few susceptible people left to infect, a CHOC Children’s infectious disease specialist says.

An instance when herd immunity broke down and a disease spread rapidly and broadly was in 2010, when a statewide whooping cough epidemic killed 10 infants and sickened 9,120 people in California. Earlier this year, the California Department of Public Health declared another statewide whopping cough epidemic.

“With the last epidemic, it was shown that there were higher rates of disease in geographic pockets where there were lower rates of vaccination,” says Dr. Jasjit Singh, associate director of pediatric infectious diseases and medical director of infection prevention and epidemiology at CHOC.

The herd immunity principle is especially important for protecting people who cannot be vaccinated, including children who are too young to be vaccinated and people with immune system problems. Of the 10 infants who died in the 2010 whooping cough outbreak, nine were too young to be vaccinated.

Unless society eliminates a disease, it’s important to keep immunizing people. If the protection given by a vaccination is removed, more and more people will become infected and spread diseases to others. In time, diseases that today are almost unknown and rare in the United States, such as polio, could return.

And though vaccinations benefit everyone, they do not offer a full guarantee that a vaccinated person won’t get a disease if exposed to an infected person, Dr. Singh says.

“Even those who have been vaccinated are at increased risk from those not vaccinated,” she says. “That’s been shown clearly with measles and whooping cough. By being in proximity or near an individual who has not been vaccinated, you are at a higher risk.”

Click here to learn more about infectious disease programs and services at CHOC Children’s.

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Childhood Vaccinations

To ensure maximum protection against diseases, children should receive vaccinations at the correct, recommended age, a CHOC Children’s infectious disease specialist tells Research 360,° a podcast highlighting research at the hospital.

In this segment, Dr. Antonio Arrieta discusses proper timing of vaccinations, dispels myths surrounding vaccinations, and details his current research at CHOC. Listen in to hear more about childhood vaccinations.

Hosted by Executive Director of Research Brent Dethlefs, Research 360° features interviews with scientists, physicians, educators, scientific news-and policy-makers to provide the listening audience with context, and scientific and social commentary intended to engage and inform.

Learn more about CHOC’s Research Institute.

Infectious Disease Clinical Trials at CHOC

Infectious_Disease_Research_CHOCClinical trials involving real patients help doctors and researchers learn the effectiveness of a new drug or medical device, and lead to advancements with potential to improve thousands of lives.

At any time, CHOC Children’s staff doctors, nurses and others are involved in about 300 clinical trials in many specialties, says Dr. Antonio Arrieta, director of infectious diseases and the director of infectious disease clinical research at CHOC.

These trials examine the safety and effectiveness of new medications, vaccines and medical devices as CHOC research physicians and their staffs seek to answer medical questions and develop new or improved drugs that can help children worldwide.

“CHOC is one of the best hospitals in the country and in the world when it comes to providing clinical care,” says Dr. Arrieta. “We also are seeking to make CHOC equally a leader in the discovery and development of new medications and medical devices for children.”

Dr. Arrieta and his team in are assessing the impact of a new and improved vaccine that would reduce invasive Pneumococcal disease, which can cause serious illnesses like pneumonia, meningitis and others.

Dr. Arrieta recently presented data from this research to the international community at a conference in Dublin hosted by the European Society for Pediatric Infectious Diseases and attended by more than 3,000 clinicians, researchers, residents and students.

“We want to share this with the international community,” Dr. Arrieta said. “This infection is of greater severity and more common in third-world countries that don’t have this vaccine.”

Orange County has seen a decline in cases of children with invasive Pneumococcal disease since the first vaccine was released in 2010. It is given to babies at the ages of 2, 4, 6 and 18 months.

Another area of research Dr. Arrieta’s team is working on involves an effort to treat a severe form of fungal infection in infants called candida, which can be fatal for premature babies.

“The current standard of care of is quite toxic so we are involved in an international trial involving a new agent that we think is going to improve the overall outcome of these babies,” he says.

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Health Workers on Alert for Measles

New measles cases continue to be reported in Measles_alertOrange County, leaving health care providers on alert for potential cases of the contagious disease.

“Any one case is troubling,” says Dr. Antonio Arrieta, CHOC Children’s director of infectious diseases. ”We shouldn’t be seeing measles in the U.S.”

The state has seen an increase in measles cases this year: Less than four months into the year, California has seen more measles cases in 2014 than in the entire year of 2010, the most recent year of available data.

Symptoms begin with high fever, transition to rash

Highly contagious, measles is transmitted through the air, Dr. Arrieta says. The disease is also strong: Contagions can remain in the air for hours after an infected person leaves an area, he says.

Symptoms typically begin to surface eight to 10 days after initial exposure to the virus, and then develop in stages. Early symptoms include a high fever – typically between 103 and 105 degrees Fahrenheit – cough, watering eyes and runny nose. A rash becomes apparent around the third day of symptoms, worsening the next day and continuing to spread over the body as the disease progresses.

People are contagious about four days before the rash begins and four days afterward, according to the Centers for Disease Control (CDC).

Measles is not treated. Instead, physicians allow the disease to run its course, while monitoring for possible complications, which are more dangerous than the disease itself. Dr. Arrieta says that most children with measles will develop pneumonia, which the CDC reports as the complication most likely to cause death in youth. One in 10 measles cases leads to ear infections, and 8 percent of sufferers report diarrhea, the CDC says.

A child with measles. Source: Centers for Disease Control
A child with measles. Source: Centers for Disease Control

Further, one child in every 1,000 measles cases will develop a brain inflammation that can lead to convulsions, the CDC reports.

Immunity ‘critical mass’ is necessary

“This highlights the problem that if you’re not immunized, you are at risk,” Dr. Arrieta says.

Dr. Arrieta emphasizes that the vaccine is safe and readily available. Following the vaccination, some children have mild reactions, such as a short-lived, low-grade fever.

Ninety percent of the population must be immune to measles to stop or prevent the spread of the disease – and that rate must factor people who cannot have the vaccine for health reasons or age, or those who don’t develop immunity from the vaccine, says Dr. Arrieta.

“If you account for many people who are not immune because they are too young, or have a condition that prevented them from getting the vaccines, then you are in a constant state of being close to that critical 90 percent,” he says. “If you account for all of those who can’t have the vaccine, and those who don’t want to, you’re getting even closer to going below 90 percent. In that case, at any given time, it will spread.”

The MMR vaccination – which covers measles, mumps and rubella – is administered in two doses. The first is given between 12 and 15 months of age, and yields a 90 percent chance of developing immunity against measles. The second dose can be given four weeks later, but is typically administered at age 4 or 5, and pushes the likelihood of measles immunity to 95 percent.

Measles widespread in foreign countries

Most measles cases in the United States – including two of Orange County’s reported cases in 2014 – are contracted by international travel, according to the CDC.

The CDC reports that measles is widespread throughout the world, including parts of Europe, Asia, the Pacific and Africa. Dr. Arrieta cautions parents that even developed countries report measles cases.

“Oftentimes, people don’t recognize that the countries they are traveling to have frequent measles cases,” he says. “Cases come from Europe, where people don’t think they’re at risk. It is a very small world these days.”

Learn more about the infectious diseases division at CHOC.

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Kids and the Immune System

girl getting a shotTHE IMMUNE SYSTEM
“Our immune system is a series of cells, tissues and organs that, throughout our lifetime, protects us from different invading pathogens and keeps us healthy and able to resist many repeated infections,” says Dr. Ashouri, a pediatric infectious disease specialist at CHOC. “When babies are infants, they get immune cells from mom through the placenta and breast milk, if they are breastfeeding. Over time, the baby’s system becomes mature and can fight off infections. A healthy lifestyle that includes getting enough rest, low stress and a balanced diet plus exercise helps to strengthen the immune system in people of all ages.”

BOOSTING BABY’S IMMUNE SYSTEM
“Breastfeeding is probably one of the best ways to help support a baby’s immune system when it’s developing,” explains Dr. Ashouri. “Getting babies the recommended vaccines at the scheduled times also helps to protect them from the different infections they are at risk for at that age. We recommend that parents and children also get a flu shot each year and are up-to-date with their Tdap vaccine to protect kids from pertussis (whooping cough). The
more people in the community who are vaccinated, the better it is for everyone. In pockets of areas where vaccine rates have fallen, there have been outbreaks of measles, whooping cough and other preventable diseases.”

KIDS AND COLDS
“Proper hand-washing is important to prevent the spread of colds and the flu virus and other types of infections. When kids can’t wash their hands, they should use a hand sanitizer to kill germs. Getting kids vaccinated against the flu also prevents kids from getting the flu,” Dr. Ashouri says. She adds, “Over time as the immune system recognizes certain viruses, it will get better at preventing infection, especially if the person has a balanced diet and good lifestyle. Taking vitamins won’t hurt either but they don’t replace a well-balanced diet.”

FAST FACTS

  • Number of infants who died in California’s 2010 Pertussis (Whooping Cough) outbreak. It was the worst outbreak in 60 years. More than 9,000 cases were reported: 10
  • Percent of the U.S. population that gets the seasonal flu (Influenza) each year: 5 to 20
  • Number of children hospitalized in the U.S. each year with respiratory infections: 500,000

View the full feature on Kids and the Immune System

Dr. Negar Ashouri
Dr. Negar Ashouri
CHOC Pediatric Infectious
Disease Specialist

PHYSICIAN FOCUS: DR. NEGAR ASHOURI

Dr. Ashouri completed her residency at CHOC, followed by a year as chief resident. After completing a fellowship in pediatric infectious diseases at Children’s Hospital of Los Angeles, she returned to CHOC. She is also a clinical instructor of Pediatrics at the UC Irvine School of Medicine.

Dr. Ashouri is involved in many research projects dealing with bloodstream infections and drug trials. She is also part of the Collaborative Antiviral Study Group. To further her research, Dr. Ashouri maintains an ongoing database of blood cultures and can frequently be found looking back through patient data and charts as she investigates how vaccines impact infections and specific risk factors for high-risk groups.

EDUCATION:
St. George’s University School of Medicine, Grenada, West Indies

BOARD CERTIFICATIONS:
Pediatric Infectious Disease

More about Dr. Ashouri

This article was featured in the Orange County Register on March 9, 2014 and was written by Amy Bentley.