Exposed to the COVID-virus? You Still Need Vaccine Shots, Northwestern Researchers
You may not know it, but you may well have been exposed to COVID-19 and never experienced a single symptom, according to Northwestern University researchers.
Even such exposure doesn’t provide adequate protection against the virus and so these people still need two doses of the vaccine, said researcher Thomas McDade, PhD, a biological anthropologist and a member of the Northwestern COVID-19 Vaccine Communication and Evaluation Network (CoVAXCEN), which convenes a panel of experts in immunology, infectious disease, epidemiology, regulatory science, and health communication.
McDade found in the SCAN (Screening for Coronavirus Antibodies in Neighborhoods) study of more than 9,000 residents of Chicago neighborhoods that nearly one in five of participants had antibodies to the COVID-19 virus even though most were not aware of experiencing any symptoms. Of all the infections, 40% were asymptomatic, and only 2.5% resulted in verified diagnoses of COVID-19.
The vast majority of patients in the study had infections that are mild or asymptomatic, and that these infections do not generate high levels of protective immunity, McDade said. “Our study shows that a single dose of current two-dose vaccines does not provide adequate protection for most people who had mild or asymptomatic cases of COVID-19,” said the researcher.
Northwestern immunologist and CoVAXCEN member Pablo Penaloza-MacMaster, PhD, who was not involved in SCAN, said, “The study suggests that one-fifth of people in Chicago may have had the virus before, at least as evidenced by serological testing.”
He said he was struck that the study uncovered social inequities in Chicago, especially between the Black and white populations. ”The study is very valuable in that context because the products of racism and segregation can be evidenced by a pandemic like this one,” he said.
Nearly 70% of the deaths from COVID-19 in Chicago have been African Americans, who make up about 30% of Chicago’s total population, according to the Chicago Department of Public Health.
McDade said antibody testing revealed no significant differences in the likelihood of viral exposure across neighborhoods. “Therefore, exposure alone cannot explain inequities in more severe cases of COVID-19 in Chicago. However, upon exposure, cases of individuals living in more disadvantaged neighborhoods are more serious and are more likely to send those with chronic medical conditions to the emergency room or hospital,” he said.
Crowded living conditions, unsafe working conditions, and/or the need to work outside the home despite stay-at-home orders may affect the rates, he said.
The SCAN study showed that reports of more flu-like symptoms forecasted higher antibody responses. However, the SCAN study found that two in three respondents had two or fewer symptoms.
“These findings suggest a relatively low level of antibody protection in the general population of previously exposed individuals, the vast majority of whom experienced no or minimal symptoms and did not require clinical care or hospitalization,” McDade said.
The ongoing SCAN study is “contactless,” meaning that the participants, recruited through the media, registered online, and were mailed test kits. The subjects used finger sticks to draw blood, which was collected and dried on filter paper and mailed to the researchers at the Institute for Policy Research and Feinberg School of Medicine, Northwestern University. Samples underwent two antibody tests.
This test platform allowed researchers to involved subjects confined to home in the midst of a pandemic, combining the accuracy of lab-based antibody testing with the convenience and reach of at-home, finger-stick blood collection.
McDade said most research on the immune response to infection involves the 1% of the patients who had COVID-19 infections severe enough to warrant hospitalization. He said SCAN is different because it studies populations with mild and asymptomatic infections in the community. “The emphasis on severe cases of clinical disease introduces an unintentional bias in our understanding of the pandemic,” he said.
SCAN researchers plan to re-test subjects to determine how long immunity lasts following vaccination and also to develop new lab methods to track emerging variants of COVID-19 using finger sticks.
The research has resulted in a half-dozen studies published in scientific journals and as non-peer-reviewed “preprints.”
The Northwestern COVID-19 Vaccine Communication and Evaluation Network (CoVAXCEN) brings together a panel of experts in immunology, infectious disease, epidemiology, regulatory science, and health communication.
Headquartered in the Institute for Global Health's Center for Global Communicable and Emerging Infectious Diseases with the cooperation of the Center for Communication and Health, CoVAXCEN seeks to achieve consensus on a variety of issues related to the safety and efficacy of COVID-19 vaccines and then produce and disseminate written materials for scientists, healthcare professionals, and the general public describing its conclusions.