CDC Real-World Study Confirms the Protective Benefits of mRNA COVID-19 Vaccines | CDC Online Newsroom


A new CDC study provides strong evidence that COVID-19 mRNA vaccines are highly effective in preventing SARS-CoV-2 infections in real-world settings among nursing staff. of health, first responders, and other key workers. These groups are more likely to be infected with the virus the majority of the population because of their work.

The study looked at the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines to prevent SARS-CoV-2 infections among 3,950 study participants in six states over a 13-week period from on December 14, 2020 to March 13, 2021.

Outcomes have shown that after the second dose of vaccine (the recommended dose range), the risk of infection is reduced by 90 percent two or more weeks after vaccination. After a single dose of any vaccine, participants ’risk of becoming infected with SARS-CoV-2 was reduced by 80 percent two or more weeks after vaccination.

It takes about two weeks after each dose of vaccine for the body to make antibodies that protect against infection. As a result, people were considered “partially vaccinated” two weeks after their first dose of mRNA vaccine and “fully vaccinated” two weeks after their second dose. These new findings of vaccine effectiveness are consistent with those from Phase 3 clinical trials conducted on vaccines before they received Emergency Use Authorizations from the Food and Drug Administration. Clinical trials examined the effectiveness of the vaccine against COVID-19 disease, while this study examined the effectiveness of the vaccine against infection, including infections with no consequent symptoms.

“This study shows that our nationwide vaccination effort is working. Approved mRNA COVID-19 vaccines provide advanced, real-world protection against infection for health care staff. our country, first responders, and other key worker needs, ”said CDC Director Rochelle P. Walensky, MD, MPH.“ These insights should give hope to millions of Americans who receive COVID-19 vaccines daily and those who have the opportunity to pull up their sleeves and be vaccinated in the coming weeks. Permitted vaccines are an important tool to help end this terrible pandemic. ”

One of the strengths of this study was its design: participants collected self-administered nasal swabs each week for the laboratory RT-PCR test, regardless of whether they developed symptoms of the disease. The researchers searched for evidence of SARS-CoV-2 infection regardless of the symptoms. A small number (10.7 percent) of the infections in this study were asymptomatic (i.e., no consequent symptoms). However, the majority of infections (58 percent) occur among people whose infections are identified by testing before they develop symptoms or know they are infected. The study showed that these two mRNA vaccines can reduce the risk of all SARS-CoV-2 infections, not just infectious symptoms.

This is important because the prevention of both symptomatic and pre-symptomatic infections among health care workers and other vital workers through vaccination can help prevent the spread of SARS-CoV-2 in those they care for or serve. Findings from this study complement previous reports that these two mRNA COVID-19 vaccines can reduce both asymptomatic and symptomatic SARS-CoV-2 infections.

This study also provided positive news about partial (single dose) vaccination. Estimating a single dose of VE in this study (80 percent) was consistent with other later VE studies following the first dose of the Pfizer-BioNTech vaccine among health care providers. Studies conducted in the United Kingdom and Israel have shown that a single dose is nearly 70 percent and 60 percent effective, respectively, against SARS-CoV-2 infection. The current results provide assurance that people will begin to develop protection from the vaccine two weeks after their first dose. The greatest protection was seen among those who received the same recommended dose of vaccine.

This CDC study was conducted through the HEROES-RECOVER network, a network of prospective cohorts that share a common protocol and methodology. This network is part of a vaccine effectiveness monitoring system made possible through federal pandemic flu preparedness funding.

This study is the first of several planned COVID-19 vaccine efficacy studies conducted by the CDC to examine the benefits of the COVID-19 vaccine in different populations and with different outcomes, such as prevention of infections, doctor visits, hospitalizations, or deaths. The results from these studies help medical and public health experts on the Advisory Committee on Immunization Practices and CDC to make important vaccine policy decisions aimed at saving lives.



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