SRU researchers develop laboratory activity to demonstrate herd immunity


Researchers at work

From left, Slippery Rock University biology professors Stacy Hrizo and Amber Eade demonstrate their laboratory activity that they developed with student researchers to teach non-science majors at SRU about herd immunity.

July 14, 2020

SLIPPERY ROCK, Pa. — People may have "heard" about herd immunity during the coronavirus pandemic, but a faculty-student research group at Slippery Rock University is actually showing what it means. Two professors and two students from SRU's Biology Department are developing a laboratory activity for non-major science classes at the University that demonstrates the suppressed spread of a viral disease after people get vaccinated.

"Even before COVID-19 started, I was teaching my students about viral transmission, immune systems and vaccination, and I wanted to take an existing epidemiology activity and figure out a way that we could teach them about what's called 'herd immunity,'" said Stacy Hrizo, associate professor of biology. "Herd immunity occurs when a large enough percentage of the population gets vaccinated against a disease, like measles or the flu, and that protects those who aren't vaccinated because it drops the rate of transmission."

Herd immunity is a popular topic in the news as public health experts try to predict how it can be achieved to fight COVID-19 once epidemiologists better understand what happens to people who were already infected with the virus and also the effectiveness of any potential vaccines.

"The rate of transmission (of COVID-19) will never be completely abolished, but we can slow it down and that's the whole point of social distancing," Hrizo said. "The goal is just to reduce the rate of spread so that those individuals who need the extra care can get the help they need. Epidemiologists are worried about relaxing the (social distancing guidelines) which can create hotspots where the virus can start to spread again."

Amber Flynn


To better teach herd immunity for non-major science classes at SRU, researchers are coming up with an activity to demonstrate this basic concept that will be used in a 100-level Science of Life course as well as Introductory Biology Laboratory class. Students who takes these classes can include, for instance, an elementary education major who someday could be teaching science.

"I want to implement activities that are really practical for the students," Hrizo said. "I want them to not hate science by the end of the semester while also learning something that could be useful. Most of them are going to have families, and when it comes time to vaccinate their children, I want them to understand the importance of it."

To develop a herd immunity laboratory activity, Hrizo partnered with Amber Eade, assistant professor of biology, and enlisted the help of two student research assistants: Aspen Flynn, a junior biology major from Sharpsville, and Cortney Dean, a senior biology major from Greensburg.

The existing activity, which demonstrates basic principles of epidemiology, models the spread of a viral disease through an unprotected population using water, sodium hydroxide and a pH indicator. As an example, 23 students in a class might have a test tube of what they believe is water with just one student's tube containing sodium hydroxide. Then, in three separate rounds, students exchange fluids with one other member of the class using pipettes and record which students they interacted with as a form of contact tracing. At the end of the activity, a pH indicator is applied, turning some of students' water pink to indicate how many were "infected" with sodium hydroxide.

SRU researchers took the activity a step further by developing another protocol to show herd immunity. They added a buffer solution that acts as a vaccine to demonstrate how vaccinating a portion of the population protects against the spread of the disease. After introducing the buffer to the activity, there are fewer vials of pink water, indicating that herd immunity is achieved. By demonstrating how 50% or 80% of the class is "vaccinated," even students who have vials that did not contain the buffer solution are less likely to contract the hypothetical virus.

"Statistics and risks are really hard to convey, so with this activity the indication goes from being clear to a hot pink color," Hrizo said. "The students really like the visual part of the experiment and that helps drive home the point."

"The lab is really simple and it makes it easy to understand how herd immunity works," Flynn said. "Instead of simply listening about how it works in a lecture, the students are actively participating in the process."

For two hours per week at the beginning of the spring 2020 semester, Flynn and Dean tested concentrations of buffer solutions to make sure that the laboratory activity would not result in any false positives. The buffer they tested is called N-morpholino propanesulfonic acid, known simply as "MOPS."

"This research is so prevalent due to the ongoing pandemic and it just showed me the importance of having people be aware of what herd immunity is," said Flynn, who plans to pursue a career as a physician's assistant after graduating. "I hadn't considered research as a career or (for graduate school), but this experience interested in taking part in more projects like this in the future and has possibly opened a new door for me."

For more information about SRU's Biology Department, visit the department's webpage.

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