Vaccination Primer

What is vaccination?

I believe the topic that is foremost on people’s minds for 2021 is vaccination: When will the vaccine for COVID-19 be available? Should a person consider getting vaccinated?

In the coming weeks and months, the vaccine for people will be administered according to a predetermined system of need. Most people will decide for themselves if and when to be vaccinated.

We are all familiar with the need for our dogs to be vaccinated as part of a healthy lifestyle. So what is vaccination actually, and how do vaccines work?

Vaccination is a simple, safe and effective way of protecting people and animals against dangerous and deadly diseases before they come into contact with them. It uses the body’s natural defenses to build resistance to specific infections and strengthen the immune system.

Vaccination is important in several ways. When we vaccinate ourselves or our dogs, we are not just protecting ourselves and our pets, but also those with whom we come in contact. Some people and dogs, like the ill, elderly or immune-compromised, are not good candidates for vaccination. They rely on the rest of us and our animals to get vaccinated and help reduce the spread of disease.

How does the body fight infection?

To understand what makes vaccines effective, it helps to first look at how bodies, both human and canine, fight illness. When germs such as bacteria or viruses invade the body, they attack healthy cells and multiply. This invasion is called an infection and is what causes the resulting illness.

The immune system fights the infection in several ways. Blood contains red blood cells, which carry oxygen to tissues and organs, as well as white blood cells, which fight infection. The white blood cells are called immune cells and consist primarily of macrophages, B-lymphocytes and T-lymphocytes.

Macrophages are white blood cells that swallow up and digest germs along with dead and dying cells. The macrophages leave behind parts of the invading germs called antigens. The body identifies antigens as dangerous and stimulates antibodies to attack them.

B-lymphocytes are defensive white blood cells. They produce antibodies that attack the antigens left behind by the macrophages. T-lymphocytes are another type of defensive white blood cell. They attack cells in the body that have already been infected.

When a body encounters a germ for the first time, it can take several days to make and use all the germ-fighting tools needed to resolve the infection. After the infection is cleared, the immune system remembers what it learned about how to protect the body against that disease.

The body keeps a few T-lymphocytes, called memory cells, that spring into action quickly if the body encounters the same germ again. When familiar antigens are detected, B-lymphocytes produce antibodies to attack them.

How do vaccines work?

Vaccines help develop immunity, which is resistance to disease, by imitating an infection. This type of infection almost never causes illness, but it does provoke the immune system to produce T-lymphocytes and antibodies. In some cases, after the administration of a vaccine, the imitation infection causes minor symptoms, such as fever, swelling and pain at the injection site. These symptoms are normal and should be expected as the body builds immunity.

Once the imitation infection goes away, the body is left with a supply of “memory” T-lymphocytes, as well as B-lymphocytes that will remember how to fight that disease in the future. However, it can take a few weeks for the body to produce these T-lymphocytes and B-lymphocytes after vaccination. Therefore, it is possible that a person or dog that is infected with a disease right before or just after a vaccination could develop symptoms and get the disease, because the vaccine has not had enough time to provide protection.

What is “herd immunity”?

When a person or dog gets vaccinated against a disease, their risk of infection is reduced, so they are far less likely to become infected with the disease and transmit it to others. As more people and dogs in a community get vaccinated, fewer remain vulnerable, and there is less possibility of passing the disease from person to person or dog to dog.

Lowering the amount of disease in the community protects those people and dogs that cannot be vaccinated due to other serious health conditions. This is called “herd immunity.”

“Herd immunity” exists when a high percentage of the population is vaccinated, making it difficult for infectious diseases to spread, since there are fewer people or dogs that can be infected. But herd immunity only works if most people and dogs are vaccinated. Consider the case of canine parvovirus. Most dogs have immunity from their mothers and from vaccination. Outbreaks are rare.

At the same time, herd immunity does not protect against all vaccine-preventable diseases. For example, tetanus, while rare in dogs, is caught from bacteria in the environment, not from other people or dogs. So those who are not immunized (vaccinated) are not protected from the disease even if most of the rest of the community is vaccinated.

How are vaccines developed and tested?

The most commonly used vaccines have been around for decades, with millions of people and pets receiving them safely every year. Every vaccine must go through extensive and rigorous testing to ensure it is safe before it can be distributed for use.

An experimental vaccine is first tested in animals to evaluate its safety and potential to prevent disease. Vaccines for human use are then tested in human clinical trials. These trials consist of three phases.

In phase I, the vaccine is given to a small number of volunteers to assess its safety, confirm that it generates an immune response, and determine the right dosage.

In phase II, the vaccine is given to hundreds of volunteers, who are closely monitored for any side effects, and to further assess its ability to generate an immune response. In this phase, some participants receive the vaccine and others do not, which allows comparisons to be made and conclusions drawn about the vaccine.

In Phase III, the vaccine is given to thousands of participants – some of whom receive the proposed vaccine, and some of whom do not, just as in phase II trials. Data from both groups are carefully compared to see if the vaccine is safe and effective against the disease at which it is targeted.

Once the results of the clinical trials are available, a series of steps is required before a vaccine may be distributed for national use. These steps include reviews of efficacy, safety and manufacturing approvals.

What is in a vaccine?

All of the ingredients of a vaccine play an important role in ensuring that a vaccine is safe and effective. These include the antigen, which is a weakened or killed form of the virus or bacteria. Antigens train the body to recognize and fight the disease if it is encountered in the future.

Adjuvants are another ingredient. These help the vaccine to work better by boosting the immune response. Preservatives are included to ensure the vaccine stays effective. Stabilizers are added to protect the vaccine during storage and transportation.

Are there different types of vaccines?

Today there are at least five main types of vaccines available in the United States. The two most common types are “live” and “killed” vaccines.

“Live” vaccines are also called “attenuated.” These vaccines have a weakened version of the living virus or bacteria. When you or your pet receive this type of vaccine, it stimulates an immune response in the body, but does not cause the disease. Examples of live, attenuated vaccines for dogs include canine distemper virus, adenovirus, parainfluenza virus and parvovirus. Human live, attenuated vaccines are measles, mumps, rubella and chickenpox vaccines.

Killed or inactive vaccines also contain the virus or bacteria. These vaccines are made by inactivating, or killing, the germ during the process of making the vaccine. They no longer have any ability to infect you or your pet. Inactivated vaccines produce immune responses in different ways than the live vaccines. Often multiple doses are necessary to build up and maintain immunity. Rabies and canine influenza virus are killed viral vaccines, while the vaccines for leptospirosis, Borrelia burgdorferi (Lyme) and Bordetella are killed bacterial vaccines. The inactivated polio vaccine for humans is a killed, inactive vaccine.

How do the COVID-19 vaccines work?

The vaccines from Pfizer and Moderna use a technique known as mRNA, or messenger RNA. Information from the Center for Disease Control says that these vaccines give instructions for our cells to make a harmless piece of what is called the “spike protein.” This protein is found on the surface of the coronavirus that causes COVID-19.

Once these vaccine instructions, or mRNA, are injected, your cells use it to make the spike protein. Then the instructions are broken down and eliminated. The protein piece is displayed on the cell surface. This triggers our immune system to make antibodies against it, just as it would if it were exposed to the real COVID-19 coronavirus. In this way, the body learns how to protect itself when and if the real virus shows up.

The mRNA vaccines do not use the live virus that causes COVID-19, nor does the mRNA get into the cell’s nucleus, which is where our DNA (genetic material) is stored.

The AstraZeneca vaccine is made from a weakened version of a common cold, the adenovirus, taken from chimpanzees. The adenovirus is genetically altered so it can’t reproduce itself. The vaccine is combined with genes of the spike protein to trigger production of antibodies against it. This allows the immune system to destroy the COVID-19-causing virus.

For the Moderna and AstraZeneca vaccines, two doses are given four weeks apart. For Pfizer’s vaccine, the two doses are given three weeks apart. The vaccines are said to take effect and provide protection about a week after the second dose. Since these are new vaccines, it is not known for sure how long the protection lasts.