Vaccines that prevent infection by SARS-CoV-2, the virus that causes COVID-19, are being rolled out around the world. Below are five things about vaccine science of which you may be unaware. Additionally, here is a video about how vaccines are determined safe.

· Two of the vaccines being developed use a technology that involves mRNA, tiny bits of genetic code that a cell uses to produce proteins. Research using mRNA as a treatment began in the 1990s to help cells replace proteins they lack due to genetic disorders. The research stalled when scientists found that mRNA treatments in animal models prompted a large response from immune system cells that could potentially hamper the treatment. Now, scientists have leveraged the ability of mRNA therapies to induce the immune responses needed for developing the current SARS-CoV-2 vaccines.

· Modern vaccines, including the most recently developed version of the shingles vaccine, may contain “adjuvants” — chemical compounds designed to enhance the immune system to respond in a certain way. Because adjuvants tend to bring on significant immune activity, they can make some people who receive vaccines containing them feel temporarily ill, including symptoms such as fatigue and pain at the vaccine site.

· Some viruses are more difficult to immunize against and develop a vaccine. That is why there is no vaccine yet for HIV and other viruses that can cause serious illnesses.

· Tests of people who were vaccinated against SARS-CoV-2 in research studies indicate that the participants produced higher levels of antibodies that neutralize the virus. By comparison, people infected with SARS-CoV-2 who develop COVID-19 have much lower levels of the neutralizing antibodies. Since data indicate that the newly developed vaccines prompt the body to develop high levels of antibodies to SARS-CoV-2, researchers say that these vaccines may offer the best opportunity to achieve immunity to the virus over large populations.

· Basic science research has resulted in many of the advances in modern vaccine science, from understanding how the virus invades a cell to the mRNA technology that began nearly 30 years ago.

Johns Hopkins Medicine scientists and clinicians are available to discuss how vaccines work, the evolution of vaccine technology and the basic science that fostered this research.