Actual Pfizer and Modern mRNA Vaccines Prevent SARS-CoV-2 Infection

Several randomized placebo-controlled phase III studies have shown that RNA (mRNA) vaccines for COVID-19 are effective in preventing serious infection with acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the efficacy of these vaccines in the prevention of asymptomatic and symptomatic COVID-19 infections is not well understood.

New Weekly report on morbidity and mortality in the publication of the American Centers for Disease Control and Prevention (CDC) states that COVID-19 mRNA vaccines are very effective in preventing SARS-CoV-2 infection in the real world. The report is based on a CDC study where it routinely tested potential groups of health workers, first aid individuals and primary and first workers for SARS-CoV-2 infections.

Participants were tested at eight different locations in the U.S. between December 14, 2020, and March 13, 2021. A total of 3,950 individuals were tested for 13 consecutive weeks regardless of symptom status and onset of symptoms associated with COVID-19 disease. Eight U.S. locations were Phoenix, Tucson, and other areas in Arizona; Duluth, Minnesota; Miami, Florida; Temple, Texas; Portland, Oregon; and Salt Lake City, Utah. Over 50% of participants were from Arizona and included physicians, primary care staff, nurses and other related health personnel, first responders and other necessities, and frontline workers.

Over 60% of the participants were women, and over 70% between the ages of 18 and 49. Almost 70% of the cohort did not have chronic health conditions. Participants had no previously documented SARS-CoV-2 infection. Almost 63% (2,479) of participants received both doses of mRNA vaccine, and 12% (477) received only the first dose of mRNA vaccine.

In unvaccinated participants, 1.38 SARS-CoV-2 infections per 1,000 person-days were confirmed by a reverse transcription-polymerase chain reaction (RT-PCR). In contrast, among fully immunized individuals tested 14 days after the second dose of vaccine, 0.04 infections per 1,000 person-days were reported. In partially immunized subjects tested 14 days after the first dose and before the second dose of the vaccine, 0.19 infections per 1,000 person-days were detected.

The results show 90% and 80% efficacy of mRNA vaccines in the prevention of SARS-CoV-2 infections in fully and partially immunized individuals.

The results of the study showed that the mRNA efficacy of the SARS-CoV-2 infection prevention vaccine was 90% in real conditions, regardless of symptom status, and 80% in partially immunized individuals. These findings have significant implications for public health because they show that approved mRNA vaccines against COVID-19 are very effective in preventing SARS-CoV-2 infections in real conditions.

The findings of the CDC study complement and build on previous study reports showing that vaccine mRNAs are also effective in reducing the risk of infection regardless of the symptom status associated with COVID-19. Reducing the risk of transmission, which is possible with asymptomatic infection or days before symptoms appear, is crucial among first responders, healthcare professionals and other key workers as they have frequent close contacts with patients as well as the public.

“Approved COVID-19 mRNA vaccines are effective in preventing SARS-CoV-2 infection in real conditions.”

The findings confirm the benefits of current vaccination efforts in preventing SARS-CoV-2 infection

The findings also showed that partial immunization offers preventive benefits with 80% efficacy, which is consistent with the results of phase III trials and multiple recent evaluations of the efficacy of mRNA vaccines for partial immunization with Pfizer-BioNTech in the UK and Israel. They are also consistent with early findings by SARS-CoV-2 employees and clinical trials against mRNA vaccination status in the United States

The significance of these findings is enhanced by the prospective design of the study and the high commitment of participants to weekly sample collection. These results on the temporary efficacy of vaccines for Modern and Pfizer-BioNTech mRNA vaccines in real conditions show that current mass vaccination efforts offer significant benefits in preventing SARS-CoV-2 infection in working-age adults. The findings also reinforce the CDC’s recommendation for full 2-dose immunization with approved mRNA vaccines.

“Vaccination against COVID-19 is recommended for all eligible individuals, which currently vary by location in the United States.”


Thompson MG, Burgess JL, Naleway AL et al. Provisional evaluations of the efficacy of BNT162b2 and mRNA-1273 COVID-19 vaccines in preventing SARS-CoV-2 infection among healthcare professionals, first responders, and other core workers – eight locations in the US, December 2020 – March 2021 MMWR Morb Mortal Wkly Rep 2021; 70: 495-500. DOI:,