Northwestern University

Study: Single COVID Vaccine Dose Insufficient for Individuals Who Had Mild Cases of Virus

Researchers studied both two-dose COVID vaccines currently available in the US in the study, which involved nearly 10,000 individuals

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Researchers at Northwestern University’s Institute for Policy Research say a new study has indicated that one dose of two-dose COVID-19 vaccines does not provide sufficient protection against the virus in individuals who had previously had mild or asymptomatic cases of the disease, meaning that those individuals are still advised to get both doses of the vaccine.

According to a press release from the researchers, the study had examined whether individuals who had previous mild or asymptomatic cases of the coronavirus could achieve a high-level of immunity with only one dose of the Pfizer or Moderna vaccine, rather than the recommended two doses.

The study did not investigate the differences between mild COVID cases and the Johnson & Johnson vaccine in terms of the robustness of immune response.

Researchers say that the study shows the importance of getting coronavirus vaccines, with the treatments serving as the best way forward toward herd immunity and making advances toward ending the pandemic.

“Our data are suggesting that the path to herd immunity really is through vaccination,” professor Thomas McDade, who was one of the individuals who helped put the study together, said.

The study found that one dose “does not provide adequate protection for most people who had mild or asymptomatic cases of COVID-19,” and that those individuals should still get both doses of the treatment.

With more pop-up vaccination clinics in Illinois, health officials hope to make additional progress in administering doses and lowering case rates. NBC 5's Jen DeSalvo reports.

The study enrolled nearly 10,000 individuals around the Chicagoland area, according to the press release. The researchers used two different types of antibody tests for the study, with one providing an accurate measure of prior exposure to coronavirus in order to help identify those who had less-severe COVID cases, and the other providing a measurement of the level of protective immunity against the virus.

The study found that mild or asymptomatic cases of COVID “generate lower levels of protective immunity” than those generated by both doses of the coronavirus vaccine.

“These mild cases and asymptomatic cases don’t generate a lot of protection, and that’s going to slow down the progress toward herd immunity (without a vaccine),” McDade said.

Individuals who had survived more severe cases, including those that required hospitalization, did generate a stronger immune response with one dose, according to researchers.

“We’re finding that the people who had severe cases of COVID clinically confirmed are responding to the first dose of vaccine with a very strong antiviral response and, again, a lot of protective immunity,” McDade said.

Researchers say that getting both doses of COVID vaccine are the best way to ensure protection against the virus itself, and of more severe outcomes in those that do contract the virus, and that the study is more proof of those arguments.

 “It’s really important that people reach that highest level of protection that they can only get through both doses of the vaccine for the vast majority of people,” McDade said.

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