Real-World Evidence Confirms Efficiency of mRNA COVID-19 Vaccines

March 31, 2021 - A new CDC study used real-world evidence to find that mRNA COVID-19 vaccines are highly effective in preventing SARS-CoV-2 infections among healthcare personnel, first responders, and other essential workers. 

The study looked at the two FDA-approved mRNA-based COVID-19 vaccines from Pfizer and BioNTech and Moderna in 3,950 study participants over a 13-week period from December 2020 to March 2021. 

Researchers found that risk of infection was reduced by nearly 80 percent two or more weeks after the first dose and by 90 percent two or more weeks after the second dose.  

“This study shows that our national vaccination efforts are working. The authorized mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation’s health care personnel, first responders, and other frontline essential workers,” CDC director Rochelle P. Walensky, MD, MPH, said in the press release.  

“These findings should offer hope to the millions of Americans receiving COVID-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead. The authorized vaccines are the key tool that will help bring an end to this devastating pandemic,” Walensky continued. 

Participants self-collected nasal swabs each week for RT-PCR laboratory testing. Researchers looked for evidence of SARS-CoV-2 infection regardless of the patient displaying COVID-19 symptoms or not.

Just over 10 percent of infections in the study were asymptomatic. But 58 percent of infections occurred among people whose infections were identified by testing before they developed symptoms or knew they were infected.

The results from the CDC study were consistent with the Phase 3 clinical trials from both Pfizer and BioNTech as well as Moderna, which were all conducted before the vaccines received FDA emergency use authorization.

At the end of November, Pfizer and BioNTech found that their COVID-19 vaccine, BNT162b2, was 95 percent effective in participants with or without prior SARS-CoV-2 infection, as well as those with and without prior SARS-CoV-2 infection.

And just a month later, Moderna announced that a second primary analysis of its COVID-19 vaccine, mRNA-1273, showed that it was 94.1 percent effective against the coronavirus. 

FDA approved both BNT162b2 and mRNA-1273 in mid-December, allowing for national distribution across the US. 

But both of the company’s Phase 3 clinical trials strictly evaluated vaccine efficacy against COVID-19 and not vaccine effectiveness against infection or infections that did not result in symptoms.

Therefore, CDC’s study demonstrated that both vaccines can reduce the risk of all SARS-CoV-2 infections, not just symptomatic infections. 

“Preventing both asymptomatic and pre-symptomatic infections among health care workers and other essential workers through vaccination can help prevent the spread of SARS-CoV-2 to those they care for or serve. Findings from this study complement earlier reports that these two mRNA COVID-19 vaccines can reduce both asymptomatic and symptomatic SARS-CoV-2 infections,” a CDC spokesperson said. 

This study also provided positive news about partial vaccination. 

For example, the one-dose vaccine effectiveness found in this study, which was 80 percent, is consistent with other recent studies following the first dose of the Pfizer-BioNTech vaccine among healthcare providers. 

Last week, the Israel Ministry of Health (MoH), Pfizer, and BioNTech shared real-world evidence showing that the BNT162b2 elicited lower incidence rates of coronavirus in individuals who were fully vaccinated. 

Specifically, researchers found that vaccine effectiveness was at least 97 percent in preventing symptomatic disease, severe or critical disease, and death. Additionally, the analysis found vaccine effectiveness of 94 percent against asymptomatic SARS-CoV-2 infections. 

For all outcomes, effectiveness was measured from two weeks after the second dose.

CDC’s study is the first of many planned COVID-19 vaccine effectiveness studies to evaluate the benefits of coronavirus vaccines in various populations across different outcomes, the agency concluded.