CDC: Herd immunity helps to protect the entire community

CDC: Herd immunity helps to protect the entire community
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Heraclitus, the 6th century B.C. pioneer of wisdom, said that no one ever steps in the same river twice. Yet, as World Immunization Week (WIW) ends, we must confront how fragile the gains in preventing and eliminating diseases can be.

Consider, for example, preliminary World Health Organization data released on April 15, which documents a 300 percent rise in measles globally from 2018 to 2019 and an increase in 2019 of more than 20,000 cases each month. While never the same, we are wading in familiar waters with measles outbreaks occurring in every region of the world.

Vaccines work

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There is strength in what we know works to prevent disease and contain outbreaks around the world. We have safe and effective vaccines to prevent many leading childhood diseases, including measles. From 2000-2017, global measles elimination efforts have prevented an estimated 21.1 million deaths, representing real progress.

Why then are we not meeting measles elimination milestones? Why are we experiencing large resurgences of measles in major regions of the world, including in the Americas ― the first and only region to achieve measles elimination status in 2016? More specifically, why do we have the recent measles outbreak in the United States?

The answer lies in access and attitudes. Most children who miss out on vaccination live in the poorest, marginalized communities; they may be in families who are on the move or impacted by conflict and emergencies. In countries where there is sufficient vaccine availability, other barriers have led to hesitancy about or refusal of certain vaccines. Many factors contribute to this uncertainty: quality or cost of health-care services, complacency about diseases that have become uncommon, and concerns about vaccine safety, fueled in some cases by the spread of misinformation about vaccines. 

An important lesson from global polio eradication efforts is that vaccination is not a one-time event. From 1988–2018, global commitment and drive to reach every child worldwide with two drops of polio vaccine yielded a 99 percent decline in wild poliovirus cases and prevented 18 million children from polio-related disability. We are staring down the last mile and inching our way to eradicating polio. Failing to vaccinate against polio, measles, yellow fever, diphtheria and other diseases, with tools we already have, threatens global progress in our efforts to prevent these illnesses and leads to death, suffering and increased economic hardship. Fragile, hard won gains are at risk, and we must act.

Protected Together 

The 2019 WIW theme "Protected Together," is a powerful call to action for parents, health-care workers and those of us in public health. We all have a role to play in ensuring all children receive all of the recommended childhood vaccines. 

Protected Together refers to the idea that by vaccinating a large percentage of the population, protection from disease is conferred, not only to those who receive vaccine, but also to those who cannot be vaccinated because they are too young, or for other reasons. If vaccination rates are high enough, “herd immunity” helps to protect the entire community. To achieve herd immunity and be Protected Together against measles, 95 percent of all eligible children must receive two doses of measles vaccine.

This mission, Protected Together, is at the heart of the work we do at the U.S. Centers for Disease Control and Prevent (CDC) to protect Americans from preventable death, disease and costly outbreaks. Public funds needed for a response to a single case of measles, for example, can reach as high as $142,000 in the United States, as detailed in a recent JAMA article, which includes case investigation, surveillance and disease control. 

Today, we have the largest number of measles cases reported in the U.S. in almost 20 years after having eliminated the disease in 2000. Measles elimination means having no continuous disease transmission for 12 months or more in the country.

Current outbreaks are linked to international travel and gaps in vaccination coverage in geographic pockets here in the U.S. Measles, a leading childhood killer globally, will exploit gaps in our ability to reach every child and adult with the recommended two doses of vaccine. We know that 90 percent of people who are exposed to the virus, who have not had measles or are under-vaccinated, will become infected and will be contagious to others for days before they develop the telltale measles rash.

We are tightly connected through global travel and trade and the best defense is to prevent diseases and ensure that we are Protected Together.

During WIW and every day, CDC celebrates all of our health heroes ― parents, health-care workers, vaccinators, innovators, donors, governments and the global public health community―and acknowledges global gains, as measured by the millions of lives saved by vaccines and the opportunity for each child to reach his or her full potential 

We also know that we must bolster our collective, focused, data driven efforts to remove barriers and improve access to and acceptance of vaccines worldwide. The best way we can continue to honor those we have lost, from children who died from preventable diseases to frontline workers who bravely committed to reach them, is to continue the work to identify and close the gaps that diseases exploit. We are better when we are Protected Together.

Rebecca Martin, Ph.D., is director of the U.S. Centers for Disease Control and Prevention’s Center for Global Health. Dr. Martin has dedicated more than 20 years of her work towards protecting people against vaccine preventable diseases, from the U.S., to Europe, to Africa and globally.