AMHERST, Mass. – Preliminary results from a University of Massachusetts Amherst statewide study reveal an asymptomatic COVID-19 infection rate last summer of 5.3% among undergraduate students and their families and 4% among faculty, staff, graduate students and their family members.
The mail-based study, led by infectious disease epidemiologist Andrew Lover, tested participants’ blood spot samples for the presence of COVID-19 antibodies. The initial findings are available on medRxiv, the health sciences preprint server for research not yet peer-reviewed.
Lover, an assistant professor in the School of Public Health and Health Sciences, says the research can help fill in the gaps of unknown exposure and sub-clinical and asymptomatic infection caused by the SARS-CoV-2 coronavirus. This kind of data has an important role in understanding how the virus spreads in the general population and can help identify vulnerable groups at higher risk of infection.
“Our numbers are consistent with other studies that have been reported from about the same timeframe,” Lover says. “Our UMass study population looks fairly similar to the statewide trends.”
The findings also can be used by infectious disease forecasters to calibrate their modeling efforts that estimate levels of population immunity over time and to inform public health guidelines, interventions and policies.
Of 1,001 study participants, 762 UMass Amherst community members from across the state filled out a survey and returned a blood sample for analysis during the first wave of the pandemic last July and August, when asymptomatic COVID-19 testing was limited.
In the primary group of undergraduates and their families, 548 people returned blood samples; in the secondary faculty/staff-related group, 214 mailed back blood samples to the team at UMass Amherst. In his lab, Dominique Alfandari, professor of developmental biology in the Veterinary and Animal Sciences Institute, conducted the enzyme-linked immunosorbent assay (ELISA) to detect SARS-CoV-2 antibodies in the blood samples.
In the undergrad-plus-family group, anti-SARS-CoV-2 IgG antibodies were detected in 36 samples, for an estimated weighed prevalence of 5.3%. In the faculty-staff-and-family group, 10 participants had detectable IgG antibodies, for an estimated adjusted prevalence of 4.0%. IgG antibodies indicate a past infection and recovery and remain longer in the blood than IgM antibodies, which rise in the first few days after infection and then fall as IgG antibodies are made. No IgM antibodies were detected in any of the samples.
Lover says that means the COVID-19 exposures that were identified by positive antibody tests were less recent, and likely months old. “It’s a good indicator that by summertime people were behaving in ways to avoid exposure,” he adds.
No link was found in either group between a positive antibody test and self-reported work duties or customer-facing hours. “We were really surprised to see no association with their job duties and customer-facing hours,” Lover says. “We suspected that people working at grocery stores and other similar roles might have a higher risk of showing infection, but this wasn’t the case.”
However, in the undergraduate student group, a positive antibody test was associated with having a self-reported illness marked by fever since February 2020, being male and being Black or American Indian/Alaskan Native.
In the faculty-staff group, the only factor linked with a positive antibody test was geographic region. “Faculty and staff living in Boston and the Boston suburbs had a higher risk, but that was not unexpected,” Lover says. “Especially early in the pandemic, Western Mass. was at much lower risk than the rest of the state.”
Lover says his team will continue to monitor COVID-19 exposure statewide through antibody testing, looking for statewide trends. He anticipates herd immunity will be reached sooner than initially thought, thanks to the development and approval of not one but several highly effective vaccines.
“Nobody expected us to have multiple vaccines available within a year. It’s astonishing,” Lover says. “If the vaccinations keep up at the rate they are at now, we should be in great shape by August.”
In addition to Lover and Alfandari, the UMass Amherst research team included biostatisticians Laura Balzer and Nicholas Reich, and graduate students Teah Snyder, Johanna Ravenhurst and Estee Cramer. The team received support from the UMass Amherst Institute for Applied Life Sciences.