Common vaccine terms and definitions: U-M experts discuss

February 26, 2021
Written By:
Laura Bailey


Throughout the pandemic, we’ve been bombarded with terms like vaccine schedule, variants, mRNA, and more. Kristin Klein, clinical professor in pharmacy and clinical pharmacy specialist in pediatric infectious diseases at the University of Michigan, and Jason Pogue, U-M clinical professor of pharmacy, define basic vaccine terms, and how these relate to the COVID-19 virus and vaccines.

Why are there two different vaccine schedules in the U.S.?

Klein: One schedule is for children under 18 years and one is for people 18 and older. Within each schedule is a subschedule broken down by age and preexisting condition. Some vaccines we give to kids, but we don’t need to give to adults.

For instance, we assume that anyone born before 1980 had chickenpox or was exposed to it, and as adults, those people don’t need the chickenpox vaccine. Today, we give the chickenpox vaccine to kids to prevent them from getting it or spreading it to others. There are other vaccines we give to kids or older adults because they’re at higher risk for getting bad disease from those viruses or bacteria.

What is a booster and why are booster shots sometimes necessary?

Klein: In some vaccines, the level of immunity decreases over time. Like the tetanus booster we get every 10 years. There are also live and inactivated vaccines, and in live vaccines (chickenpox, measles/mumps/rubella) the body has a more profound immune response and immunity lasts longer. We now recommend two doses of MMR and chickenpox in childhood, and at least for now, that’s all you need for the rest of your life. That immunity seems to last for years and years.

Will we need a COVID booster?

Klein: For the COVID vaccine, we don’t know yet if we’ll need additional doses of vaccine.

Often, we hear the term variant in connection with COVID. What is a variant?

Klein: This term sounds scary, but it’s simply a different strain or a slight change in the strain of a virus. What’s happening with the coronavirus is not unusual. We see this all the time with influenza; that’s part of the reason we get a flu shot every year. Occasionally we have a virus like H1N1 in 2009, where we’ll see a brand new strain of virus or a strain we haven’t seen in a hundred years.

Pogue: It helps to think of variants as falling into one of three buckets. The first is when a mutation offers no advantage to the virus, so it’s not a concern. This is actually the most common type of mutation but because it doesn’t lead to enhanced replication, transmission or immune evasion, it is not impactful.

The second is a variant that’s advantageous in some way for the virus, but does not escape our immunity. One example is the B.1.1.7, the U.K. variant. It’s more transmissible, so can quickly become the dominant version of the virus in a community. However, the available data suggests that B.1.1.7. does not evade our immunity, either from previous infection or vaccine-induced, so would not require a new or modified vaccine. The third variant affords the virus the ability to escape our immune response.

Does each variant require a new or modified vaccine?

Pogue: No. The third type of variant affords the virus the ability to escape our immune response, which depending on the degree of escape might require a new or modified vaccine. This is the concern with B.1.351, the South Africa variant, as well as the P.1 or Brazil variant. We’re still learning the degree to which these variants impact vaccine-induced or natural immunity, and how well current vaccines protect against this variant.

Do you think these mutations in the South Africa/Brazil variants will require a modified vaccine and if so will it be tough to do so?

Pogue: It’s too soon to know. We’re still learning about the degree and duration of protection that either natural infection or vaccine-induced immunity provides. Even though it feels like forever, we’re still relatively young in the COVID-19 universe. We have not had a chance to see how it behaves amid large-scale population-based immunity. However, should an updated booster be needed against these vaccines, I think one of the nice things about the mRNA platforms is that they should be relatively flexible to allow this.

What is the mRNA platform?

Klein: The Pfizer/BioNTech and Moderna COVID-19 vaccines are messenger RNA vaccines, which doesn’t use any part of the virus or bacteria at all. They target a protein in the virus and teach the immune system to recognise that protein, and make antibodies against the protein. The next time the body sees a similar protein, it triggers the immune response. As long as the virus has that spike protein, your body should be able to recognize it.

What else would you like people to know about vaccines in general, or the COVID vaccines?

Klein: This might be a good opportunity to emphasize that pharmacists are very capable of vaccinating people. Our students receive 10 hours of pre-work and 10 hours of live training, where they are mentored in and practice their technique. Independent and major pharmacy chains are in a separate distribution plan, which means they may have different vaccine allotments than health departments or private practices.