• Vaccines work by training your immune system to recognize, attack, and disable especially dangerous pathogens like the flu, meningitis, and polio.
• There are different types of vaccines based on what disease they’re targeting and the demographic most affected by it.
• In addition to protecting the individual, vaccines help create herd immunity, which protects large communities – especially high-risk groups – from infection.
• Visit Insider’s Health Reference library for more advice.

Vaccines are vital to fighting disease, not only for individuals but also for entire communities. For reference, the World Health Organization suggests that vaccines prevented at least 10 million deaths worldwide between 2010 and 2015. 

However, there’s a lot of misinformation around how vaccines work. For example, there’s the misconception that getting a flu a vaccine infects you with the flu, when in reality it exposes you to virus particles that are already dead, or too weak to cause infection. 

Moreover, the process of making a vaccine is difficult, complicated, and takes time. Here’s what you need to know about how different types of vaccines work to protect you from potentially deadly infections. 

How vaccines work with the immune system

Your immune system is your body’s natural defense against toxic or infectious intruders – clinically called agents. Normally, when you get sick, these agents trigger your immune system, which sends a flood of antibodies to attack the invaders. However, some intruders are more dangerous than others and can overwhelm your immune system causing permanent abnormalities or, in extreme cases, death. That’s where vaccines come in.

Vaccines give your immune system a boost against specific infections known to be especially dangerous to human health like the flu, meningitis, and poleo. Vaccines work by training your immune system to recognize harmful pathogens without actually infecting you. That way, when you come into contact with that pathogen later, your body is prepped and ready with the right disease-fighting antibodies to fight off the infection. 

Your body produces different kinds of antibodies for different tasks. When it comes to attacking germs and viruses, that's left to a group of antibodies called b-lymphocytes (aka B-cells). Sometimes these B-cells need back up, which is where another group called T-cells come in. T-cells help B-cells make antibodies and they can also destroy a cell that has already become infected by a virus or bacteria. And vaccines are what help you build a specialized army of B- and T-cells to target specific diseases.

Vaccines are especially important for infants whose immune system isn't as strong and may not be able to fight off infection like an adult. That's why children are administered a series of vaccinations at an early age. Early vaccination helps children fight off infections like chickenpox and measles before their immune system has time to build its own, natural, immune response. Vaccines have improved childhood mortality rates significantly since their invention for this reason. 

However, some vaccines essentially wear off or need multiple shots to fully work. These are called "boosters" or re-vaccinations and are needed to remain effective in the human body. Essentially your immune system has its own kind of memory that allows it to recall how to fight off infections. Boosters help jog the immune system's memory.  Meningitis is one such vaccine that requires a boost. Usually, you'll get a meningitis shot when you're a child and then get one booster when you're a teenager.  

Types of vaccines

Not all viruses are alike, and how scientists create a vaccine depends on several characteristics of the disease including: 

• How it affects the body
• How the immune system reacts 
• The population most affected by it

There are four types of vaccines based on how they affect your immune system. Here's a list of all four types and examples of each:

Each of the vaccine types has different strengths and weaknesses, says Brendan Wren, a professor of microbial pathogenesis at the London School of Hygiene & Tropical Medicine, and choosing the right one is vital. 

For example, "live attenuated strains are required to deliver a strong and suitable immune response, but live attenuated strains could have safety issues," Wren says. The safety issues around live attenuated strains has to do with the fact that these vaccines contain a weakened version of the pathogen it's protecting against. In very rare cases, these pathogens, though weakened, may cause infection. That's why, as a precaution, these vaccines are not generally administered to people who are immunocompromised or to people who are pregnant.

How vaccines save lives

The CDC says that, due to vaccines, the average number of prevented childhood deaths per year is a little under 800,000. 

While vaccines are important to protect your own health, they also protect your community at large. Vaccines enable something called "herd immunity" which essentially means that mass vaccinations of the public create a barrier of immunity that shields more at-risk groups from disease as less people are likely to carry illness. 

Insider's takeaway

Vaccines enable the body to fight off illnesses, and therefore prevent serious complications and death from diseases. The polio vaccine is an example of a vaccine that was able to nearly eradicate the disease following mass vaccination efforts worldwide. Without these efforts there still may be thousands of cases of this paralytic disease.

There are currently 31 vaccines available in the US that have been developed since the first vaccine - the smallpox vaccine - was created in the 18th century. 

Despite some controversy about vaccines - such as the scientifically unfounded correlation to autism in infants - they protect the population from widespread illness and death and are a necessary part of public health measures. 

Related stories about preventing the spread of disease:

• What is a vaccine? Why vaccines are important and how long they last
• How do viruses spread and how to protect yourself against infection
• What is a ventilator? How the breathing machine can save lives
• How respirators work, and who needs to wear a face mask
• Can you reuse a face mask? It won't be as effective if you do