What Purpose Do Vaccinations Serve?

The purpose of vaccinations is to protect you from infectious diseases like measles, whooping cough, and influenza. Vaccines train your immune system to recognize and fight specific disease-causing organisms known as pathogens, which include viruses and bacteria.

How Your Body’s Immune System Fights Disease

The body’s immune system has several lines of defense to help protect against disease and fight off infections. They are broadly classified into two parts: innate immunity and adaptive immunity.

Innate Immunity

Innate immunity is the part of your immune system you are born with. It is your body’s frontline defense against disease. Your innate immune system consists of immune cells that are immediately activated when a pathogen appears. These cells don’t recognize specific pathogens; they simply know how to spot and attack germs.

The defense system includes white blood cells known as macrophages (macro- meaning “big” and -phage meaning “eater”) and dendritic cells (dendri- meaning “tree,” which describes their branch-like appearance).

Dendritic cells, in particular, are responsible for presenting the pathogen to the immune system to trigger the next stage of the defense.

Adaptive Immunity

Also known as acquired immunity, the adaptive immune system responds to pathogens captured by frontline defenders. This part of the immune system produces disease-specific proteins (called antibodies) that either attack the pathogen or recruit other cells (including B-cell or T-cell lymphocytes) to the body’s defense.

Antibodies are “programmed” to recognize the attacker based on the antigens (specific proteins) on its surface. These antigens distinguish one pathogen type from another.

Once the infection has been controlled, the immune system leaves behind memory B-cells and T-cells to act as guards against future attacks. Some of these are long-lasting, while others wane over time and begin to lose their memory.

How Vaccines Help Your Body Recognize and Defend Against Pathogens

When the body is naturally exposed to everyday pathogens, it can gradually build a robust defense against a multitude of diseases. Alternatively, the body can be immunized against disease through vaccination to achieve this same defense. The primary difference between these two paths to immunity is that with vaccination you don’t have to become sick first in order to develop immunity.

Vaccination involves the introduction of a substance that the body recognizes as the pathogen, preemptively triggering an immune response. In essence, the vaccine “tricks” the body into thinking it is being attacked, though the vaccine itself does not cause disease.

After vaccination, your body maintains memory cells that protect you if you encounter that pathogen again. Vaccines essentially tailor your body’s immune defenses to protect against many infectious diseases, either by blocking them entirely or reducing the severity of their symptoms.

Vaccines may contain:

• A dead or weakened form of the pathogen
• An isolated part of the pathogen
• A substance produced by the pathogen

There are also therapeutic vaccines that activate the immune system to help treat certain diseases after they have developed.

There are currently three therapeutic vaccines approved by the U.S. Food and Drug Administration (FDA). These are used in the treatment of prostate cancer, invasive bladder cancer, and oncolytic melanoma. Other therapeutic vaccines are currently being explored to treat viral infections like hepatitis B, hepatitis C, HIV, and human papillomavirus (HPV).

What Are the Different Types of Vaccines and How Do They Work?

Although the goals of all vaccinations are the same—to trigger an antigen-specific immune response—not all vaccines work in the same way.

There are six broad categories of vaccines currently in use and numerous subcategories, each with different delivery systems (vectors) and different ways of triggering the immune system.

Live Attenuated Vaccines

Live attenuated vaccines use a whole, live virus or bacterium that has been weakened (attenuated) in order to make it harmless to people with healthy immune systems.

Once introduced into the body, the attenuated virus or bacteria triggers an immune response closest to that of a natural infection. Because of this, live attenuated vaccines tend to be more durable (longer-lasting) than many other types of vaccine.

Live attenuated vaccines can prevent diseases such as:

Inactivated (Killed) Vaccines

Inactivated vaccines, also known as whole-killed vaccines, use whole viruses that are dead. Although the virus cannot replicate, the body will still regard it as harmful and launch an antigen-specific response.

Inactivated vaccines are used to prevent the following diseases:

Subunit Vaccines

Subunit vaccines use only a piece of the germ or a bit of protein to spark an immune response. Because they don’t use the whole pathogen, side effects usually milder than they are with live vaccines. That said, multiple doses are typically needed for the vaccine to be effective.

These also include conjugate vaccines, in which a weak antigen (often a bacterial sugar molecule, or polysaccharide) is linked to a protein to boost immune response.

Diseases prevented by subunit vaccines include:

Toxoid Vaccines

Toxoid vaccines help protect you against the toxins that some pathogens produce when inside the body. These vaccines use a weakened version of the toxin—called a toxoid—to help the body learn to recognize and destroy these substances before they cause harm.

Toxoid vaccines licensed for use include those that prevent:

Viral Vector Vaccines

Viral vector vaccines use a harmless virus such as an adenovirus (a type of cold virus) to deliver genetic instructions that tell your body how to make an antigen, which then triggers an immune response. The virus used for delivery has been modified so it can’t replicate, which means it isn’t capable of making you sick.

Viral vector vaccines help protect against:

The Janssen (Johnson & Johnson) viral vector COVID‑19 vaccine is no longer available in the United States or Europe, primarily due to low demand.

mRNA Vaccines

Newer mRNA vaccines involve a single strand molecule called messenger RNA (mRNA) that delivers genetic coding to cells. These instructions tell the cells how to produce a specific antigen, such as the SARS‑CoV‑2 spike protein, which trains the immune system to recognize and fight the virus.

The mRNA is encased in a fatty lipid shell. Once the coding is delivered, the mRNA is naturally broken down by the cell.

Currently approved mRNA COVID-19 vaccines include:

• Pfizer-BioNTech Comirnaty (tozinameran)
• Moderna Spikevax (nucleoside-modified mRNA vaccine)

Are Vaccines Safe?

Despite claims and myths to the contrary, vaccines work and, with few exceptions, are extremely safe. Throughout the development process, there are multiple tests vaccines must pass before they arrive at your local pharmacy or healthcare provider’s office.

Prior to being licensed by the FDA, manufacturers undergo stringently monitored phases of clinical research to ascertain whether their vaccine candidate is effective and safe. This typically takes years and involves no fewer than 15,000 trial participants.

After a vaccine is licensed, the research is reviewed by the Advisory Committee on Immunization Practices (ACIP)—a panel of public health and medical experts coordinated by the Centers for Disease Control and Prevention (CDC)—to determine whether it is appropriate to recommend the vaccine and to which groups.

Even after the vaccine is approved, it will continue to be monitored for safety and efficacy, allowing ACIP to adjust its recommendations as needed. There are three reporting systems used to track adverse vaccine reactions and channel the report to ACIP:

• Vaccine Adverse Event Reporting System (VAERS)
• Vaccine Safety Datalink (VSD)
• Clinical Immunization Safety Assessment (CISA) Network

What Are the Benefits of Getting Vaccinated?

Vaccinations protect you from infectious diseases and also help stop the spread of these diseases to other people in your community.

Some people cannot get certain vaccines because they are too young, elderly, have a weakened immune system, or have other serious health conditions. When most healthy people in a community have been vaccinated, however, the disease is much less likely to spread. This helps protect everyone, even those who can’t get the vaccine. This is referred to as herd immunity.

The “tipping point” varies from one infection to the next but, generally speaking, a substantial proportion of the population must be vaccinated in order for herd immunity to develop.

Herd immunity is what led public health officials to eradicate diseases like smallpox that used to kill millions. Even so, herd immunity is not a fixed condition. If vaccine recommendations are not adhered to, a disease can re-emerge and spread throughout the population again.

Measles, for example, was declared eliminated in the United States in 2000. Declines in vaccination rates, however, have contributed to a recent re-emergence of this disease.

Unfounded claims of vaccine harms from anti-vaccination proponents have contributed to the declines in herd immunity. These groups have incorrectly asserted that vaccines are not only ineffective (or created by corporate profiteers) but may also cause conditions like autism. Research has consistently demonstrated that there is no link between vaccines and autism.

What Should You Discuss With Your Doctor Before You Get Vaccinated?

The bulk of clinical evidence shows that the benefits of vaccination far outweigh any potential risks and that almost everyone should get the recommended vaccines at the recommended times.

However, it is important to advise your healthcare provider if you are pregnant, are immunocompromised, or have had an adverse reaction to a vaccine in the past. In some cases, a vaccine may still be given, but in others, the vaccine may need to be substituted or avoided.