Those Vaccinated Have Reduced COVID-19 Severity, Disease Length and Viral Load

A single dose of mRNA vaccine proved 81% effective against a SARS-CoV-2 infection.

A recent paper authored by investigators from the University of Arizona Health Sciences has shown that individuals who are vaccinated against COVID-19 are likely to have a shorter course of disease, have more mild symptoms and have a lower viral load than unvaccinated people.

The paper was published in The New England Journal of Medicine.

"If you get vaccinated, about 90% of the time you're not going to get COVID-19," Jeff Burgess, associate dean for research and a professor at the Mel and Enid Zuckerman College of Public Health and principal investigator of the Arizona Healthcare, Emergency Response, and Other Essential Workers Surveillance (AZ HEROES) study said. "Even if you do get it, there will be less of the virus in you and your illness is likely to be much milder."

The paper analyzed data from 2 ongoing studies that are being funded by the US Centers for Disease Control and Prevention (CDC). The 2 studies are the AZ HEROES study and the Abt Associates-led Research on the Epidemiology of SARS-CoV-2 in Essential Response Personnel (RECOVER) study.

The participants of the studies are all health care personnel, first responders, and other essential and frontline workers in eight US locations, who are undergoing weekly nasal swab and quarterly blood tests for COVID-19.

The paper includes data from December 14 to April 10 and found that 2 doses of an mRNA COVID-19 vaccine were 91% effective against infection with SARS-CoV-2. The findings also showed that vaccinated individuals had infections detected for 1 week compared to 2 or more weeks in those not vaccinated.

Additionally, the risk of having COVID-19 with an accompanying fever was 58% lower for vaccinated participants.

"We are still seeing the same high levels of vaccine effectiveness, so we feel good about that," Burgess said. "But more importantly, we've added a number of measures of the severity of infection among individuals who have been vaccinated as a comparison to those who haven't, and we measured how much virus there is and for how long."