What is a vaccine? Why vaccines are important and how long they last

A vaccine is part of a germ that is exposed to your immune system in a safe way so that it can learn how to fight off that harmful pathogen and protect your body from it in the future.
Vaccines are important because they can greatly reduce and prevent the spread of disease – they have even eradicated some life-threatening diseases worldwide.
Here are five of the most important vaccines ever, according to public health experts.
This article was medically reviewed by Alex Berezow, PhD, a microbiologist at the American Council on Science and Health.
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Vaccines are the most effective way to prevent the spread of disease. Because of these immunizations, life-threatening diseases like smallpox have been eradicated worldwide.

“We have so many vaccines that are effective, that we are not seeing vaccine-preventable illnesses like we were in the past,” says Joseph Comber, PhD, a biology professor at Villanova University.

For reference, the World Health Organization (WHO) estimates that vaccines stop 2 to 3 million deaths annually. And that’s only possible due to the large number of immunizations being administered.

Here’s what you need to know about why vaccines are important, including five of the most significant ones ever developed.

What is a vaccine?

A vaccine is a part of a virus or bacteria that is exposed to your body in a safe and effective way. It is often a weakened or dead part of the germ. Then, if we encounter those germs in our day-to-day life, the immune system will know precisely how to fight them off.

When a germ or pathogen does enter your body, your immune system quickly recognizes there's an intruder and works to prevent it from spreading. As the immune system embarks on this effort, it makes specialized memory cells that can recall a pathogen or germ.

"The next time that same pathogen or germ gets into our bodies, the memory cells can respond much more quickly," explains Comber.

Vaccines mimic this natural process by introducing a pathogen to your immune system in a form that can't cause sickness. "Without ever being sick, we're educating our immune system on how to remember a germ," Comber says.

Why vaccines are important

Vaccines are important to protect babies and children from illnesses, as they don't yet have a fully developed immune system. That's why the vaccination process begins at birth for many immunizations.

For example, in 2018, 116.3 million infants received the diphtheria-tetanus-pertussis vaccine, per the WHO. The effectiveness of vaccines, however, depends on everyone continuing to get them - as some vaccines aren't safe to administer until babies are 12 months old.

"It's really important to get vaccines - not only are you protecting yourself and your kids, but you're also protecting other people in the community," says Comber.

The most important vaccines ever

For scientists around the world, the race is on to develop a vaccine for the coronavirus. Designing and testing a vaccine is a slow process - but once a vaccine is available, it will slow the spread of the virus, limit the need for self-isolation, and allow the world to get back to life as normal.

"The COVID-19 pandemic is a living testament to the need for vaccines," says Kirsten Hokeness, PhD, professor and chair of the department of science and technology at Bryant University.

Any vaccine is an achievement, notes Comber. Some, however, stand out as being historically significant. Here are five of the most important vaccines ever developed:

The smallpox vaccine

Smallpox was the first successful vaccine, developed in 1796 by Edward Jenner. "Jenner really popularized the procedure, making it a common practice," says Hokeness.

The WHO describes smallpox as "one of the deadliest diseases known to humans." This virus leads to flu-like symptoms followed by pus-filled blisters on your body, per the Mayo Clinic. Hokeness notes that historically, it killed three out of every 10 people who contracted the disease.

Smallpox is the only disease ever to be eradicated worldwide. That means that these days, no one receives the smallpox vaccine - it's no longer necessary. This elimination of the disease "is one of the greatest international public health achievements," says Hokeness.

The polio vaccine

When the polio vaccine became available, people lined up around the block to get it, Comber says. "The visions of children using iron lungs to survive are permanently ingrained in our history of infectious disease," says Hokeness.

Children are particularly at risk for poliomyelitis, a highly infectious virus that spreads through contact with someone who has the infection, as well as through contaminated food and water, says Hokeness. In some people with polio, it can lead to paralysis, which can be permanent, per the WHO.

Today, the Centers for Disease Control and Prevention (CDC) recommends that children get four doses of the polio vaccine, beginning at two months of age. There hasn't been a new polio case in the United States since 1979, Hokeness says. Around the world, the number of cases has decreased as well - in 2018, there were just 33 cases.

The MMR vaccine

Today, kids get two doses of the MMR vaccine, which protects against measles, mumps, and rubella - one at 12 to 15 months, and a second dose at ages 4 to 6. The vaccine is highly effective against the measles, which is a very contagious respiratory virus.

"It is so contagious that if one person has it, up to 90% of the people around him or her will also become infected if they are not protected," notes the CDC.

And the consequences are severe: measles can lead to pneumonia, encephalitis (brain swelling), and in some cases death, says Hokeness. Vaccines for measles became available in 1963. Before vaccines were available, 3 to 4 million people got the measles annually.

In the year 2000, thanks to widely available and effective immunizations, measles was declared eradicated in the United States. More recently, however, measles outbreaks began to occur again. In 2019, there were 1,282 cases of measles in the United States, per the CDC.

This is a result of a few factors. Some vaccines, like measles, offer waning immunity, and you may need to get a booster, which is a follow-up shot that supplements the initial vaccine. In addition, misconceptions about vaccines have led some parents to not vaccinate their children, and since the virus is not eradicated world-wide, travel to hotspots can lead to outbreaks.

"The recurring outbreaks of this disease have also fostered the paramount need for vaccinations to protect our population and the risks we face from lapses in vaccinations," says Hokeness.

The Tdap vaccine

The Tdap vaccine protects against three diseases: tetanus, diphtheria, and pertussis. All three of these diseases are caused by bacteria and have the potential to be deadly.

Pertussis - better known as whooping cough - can be life-threatening for babies, although it's not as serious for adults. Until they are old enough to get the vaccination, "infants rely on everyone around them being vaccinated against whooping cough," says Comber, who lists the pertussis vaccine as being especially significant.

During each pregnancy, women need to get the Tdap vaccine, as the immunization may help protect the baby. Anyone who will be around a baby - friends, family, healthcare professionals, daycare employees, and so on - should also make sure they have this vaccine and any necessary booster.

Before pertussis vaccinations, about 200,000 US children became sick with it each year, and about 9,000 children died as a result of the disease. Now, per the CDC, there are only about 10,000 to 40,000 cases each year, and very few deaths.

The HPV vaccine

The history of the HPV vaccine is not so distant - this vaccine first became available in 2006. Human papillomavirus, or HPV, is the most common sexually transmitted infection in the US, with 14 million Americans contracting HPV each year.

There are many strains of this virus - some of them are linked with cancer, including cervical cancer, penile cancer, and cancers of the back of the throat. Vaccination has led to a 29% decrease in cervical cancer, according to a 2018 study from the American Journal of Preventive Medicine.

"This vaccine is one of the closest things we have to a cure for cancer," says Hokeness. The HPV vaccine is given in either two or three doses to children and teens - getting this immunization at a young age, before sexual encounters, is what makes it effective.