How Are Vaccines Made and Why Do They Work?

In their book Vaccines: What Every Parent Should Know, Dr. Paul Offit and Dr. Louis Bell take the complex question of how vaccines are made and answer it in a way we can all understand:

Vaccines are made by taking viruses or bacteria and weakening them so that they can’t reproduce (or replicate) themselves very well or so that they can’t replicate at all. Children given vaccines are exposed to enough of the virus or bacteria to develop immunity, but not enough to make them sick. There are four ways that viruses and bacteria are weakened to make vaccines:

  • Change the virus blueprint (or genes) so that the virus replicates poorly. This is how the measles, mumps, rubella, and varicella vaccines are made. The virus blueprint is changed by a technique called cell culture adaptation [adapting a virus to grow in specialized cells grown in the lab instead of the cells it normally grows in]. Because viruses can still, to some extent, make copies of themselves after cell culture adaptation (and therefore are still alive), they are often referred to as live, attenuated (or weakened) viruses.

  • Destroy the virus blueprint (or genes) so that the virus can’t replicate at all. This is how the “killed” polio vaccine (or polio shot) is made. Vaccine virus is made by treating polio virus with the chemical formaldehyde. This treatment permanently destroys the polio genes so that the virus can no longer replicate.

  • Use only a part of the virus or bacteria. This is how the Hib, hepatitis B, and (in part) pertussis vaccines are made. Because the viral or bacterial genes are not present in the vaccine, the viruses or bacteria can’t replicate.

  • Take the toxin that is released from the bacteria, purify it, and kill it so it can’t do any harm. Some bacteria cause disease not by replicating but by manufacturing harmful proteins called toxins. For example, bacteria like diphtheria, tetanus, and pertussis (whooping cough) all cause disease by producing toxins. To make vaccines against these bacteria, toxins are purified and killed with chemicals (such as formaldehyde). Again, because bacterial genes are not part of the vaccine, bacteria can’t replicate.

Vaccine Boosters

Because the immune response from some vaccines may decrease over time, vaccines known as “boosters” are sometimes given to restore the immune response against that particular germ. Protective immunity lasts longer when boosters are given.

Tetanus boosters, for example, are recommended every 10 years starting at age 10 or 11. A study published in May 2002 by the Annals of Internal Medicine revealed that millions of Americans are vulnerable to tetanus and diphtheria infections because their booster shots have not been kept up to date.

On other fronts in the vaccine field, scientists are trying to find new ways of producing vaccines, particularly using biotechnology and genetic engineering. These new methods would make it unnecessary to produce large quantities of the dangerous pathogens to make vaccines.

Passive Immunity

In addition to natural or “vaccine-induced” immunity to diseases, there is also “passive” immunity. Passive immunity occurs when someone is injected directly with large quantities of antibodies that are ready to immediately fight a specific virus or bacteria.

These antibodies go to work immediately against any antigen or pathogen. There is no waiting period, as is needed by some vaccines, before sufficient antibodies are produced. However, protection from these antibody injections is temporary. Once the antibodies are cleared from the body, no new antibodies are made.

Doctors use this approach to treat people who have been exposed to hepatitis B, hepatitis A and rabies. Babies born to mothers with hepatitis B are immediately treated with hepatitis B antibodies (called HBIG or hepatitis B immune globulin) and simultaneously immunized against hepatitis B to prevent any infection that might have occurred during the birth process.

Next Page: Monitoring Vaccines for Safety

Previous Page: The Immune System vs. Germs


Important disclaimer: The information on is for educational purposes only and should not be considered to be medical advice. It is not meant to replace the advice of the physician who cares for your child. All medical advice and information should be considered to be incomplete without a physical exam, which is not possible without a visit to your doctor.

Immunizations stop
disease from spreading.

Check with your family
doctor to see if you could benefit.