Types of Vaccines

The vaccine your parents got as a kid may not be the same as the one that you got. Vaccine technology keeps getting better, and new vaccines are coming out all the time. Each version is made to be safer and work better than the last. And with new methods, we’ve been able to make vaccines against viruses that weren’t possible with older methods.

No matter how they’re made, all vaccines are based on the same idea. Show a virus, or parts of it, to the body’s immune system—without making you sick. The immune system recognizes a virus by the parts on its surface. Once the body learns to recognize these parts, it’s protected from the real virus.

Need a refresher on immunity? Visit How Vaccines Work.

The descriptions here focus on vaccines for viruses. But many of the same approaches are used in vaccines against bacteria and other parasites. Some are even used to treat cancer.

Which Approach Is Best?

When you need to make a new vaccine, you can’t know in advance which approach will work best. Only 6% of vaccines that started the tested process have made it through all the way to patients. That’s why it’s common for multiple groups to start working on vaccines at once, each using a different approach. Trying lots of ideas raises the chance that one will work.

Within the first months of the COVID-19 pandemic, more than 90 vaccines were being worked on around the world, using eight different approaches. By late October, that number had grown to 177, and 54 had moved into human trials (being tested in people). Many of these possible vaccines used newer technologies never before used in people, like nucleotide vaccines and recombinant vector vaccines. That’s because these technologies can lead to vaccines more quickly—very important when a new virus is spreading across the globe. And if more than one vaccine works? All the better for getting more doses out to the people who need them!

Veterinary Vaccines

New approaches are often tried first in vaccines for animals—including for farmed animals, pets, or wild animals. For example, years before the first recombinant vector vaccine (for Ebola) was ready for use in people, the approach was used in vaccines for animals. They included a distemper vaccine for dogs, a rabies vaccine for wildlife, and a MERS vaccine for camels. Animal vaccines keep animals healthy. They are also a way to test approaches that may one day be used in people.

Poultry and livestock are regularly vaccinated against multiple viruses. This practice not only helps keep the animals healthy, it also keeps animal viruses from spreading to people. For example, birds can carry influenza viruses that may be able to spread to people.

Real-World Logistics

When a new vaccine is being developed, the top concerns are that it should be safe and work well. But there are other factors to think about. Cost is one. For example, vaccines grown in bacteria cost less to make than those made in cells from mammals. And there are logistics to think about. For example, a new childhood vaccine needs to fit into the current vaccination schedule.

Factors that affect where and how a vaccine can be used include how stable it is and how long it lasts when being stored. If a vaccine needs to be kept cold, it is difficult to bring it to remote areas that may not have electricity. How the vaccine is delivered is also important. For example, a vaccine that’s a shot must be given by someone who has training. But one that’s dropped into the mouth can be given by anyone.

For a vaccine to work for the people who need it, vaccine makers must think about all of these factors and more, right from the start.

Why a Shot in the Arm?

Many vaccines are given as a shot in the arm. Shots are easy to give, cause few side effects, and for most vaccines, work very well. This way of delivering a vaccine is also called “intramuscular injection.” Injected into a muscle, vaccine molecules stay around for a while, and immune cells can easily “find” them.

For some vaccines, a different delivery method is better. Other options are a shot under the skin (subcutaneous), a spray into the nose, drops that are swallowed, and more. Most DNA vaccines are delivered by electroporation. In this method, tiny needles cause small holes in the skin and deliver DNA. Then a weak electrical current makes tiny holes in cells for a short time to get the DNA inside.

For some vaccines, such as those made from weakened viruses, it’s best to deliver them to the tissues that the virus normally infects. The vaccine for rotavirus, a virus that infects the gut, is given by mouth. FluMist®, a weakened influenza vaccine, gets sprayed into your nose.


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