Two weeks after the 1st dose, recipients are about 80% protected against infection, and 2 weeks after the 2nd dose, that protection rises to roughly 90%.
A remarkable and reassuring outcome, particularly when you consider how many vaccines have been administered over the past 3 months in the United States.
Despite this excellent showing - even though I'm scheduled to receive my 2nd dose this Friday. and will be considered `fully vaccinated' by mid-April - I still intend to take the recommended precautions when in public (see CDC guidelines When You’ve Been Fully Vaccinated).
Two stops this morning. First, excerpts the press release from the CDC on this study, followed by a link and excerpts from the MMWR report.
Study involved health care personnel, first responders, and essential workers in six statesPress ReleaseEmbargoed until: 11 a.m. ET, Monday, March 29, 2021A new CDC study provides strong evidence that mRNA COVID-19 vaccines are highly effective in preventing SARS-CoV-2 infections in real-world conditions among health care personnel, first responders, and other essential workers. These groups are more likely than the general population to be exposed to the virus because of their occupations.The study looked at the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines in preventing SARS-CoV-2 infections among 3,950 study participants in six states over a 13-week period from December 14, 2020 to March 13, 2021.Results showed that following the second dose of vaccine (the recommended number of doses), risk of infection was reduced by 90 percent two or more weeks after vaccination. Following a single dose of either vaccine, the participants’ risk of infection with SARS-CoV-2 was reduced by 80 percent two or more weeks after vaccination.It takes about two weeks following each dose of vaccine for the body to produce antibodies that protect against infection. As a result, people are considered “partially vaccinated” two weeks after their first dose of mRNA vaccine and “fully vaccinated” two weeks after their second dose. These new vaccine effectiveness findings are consistent with those from Phase 3 clinical trials conducted with the vaccines before they received Emergency Use Authorizations from the Food and Drug Administration. Those clinical trials evaluated vaccine efficacy against COVID-19 disease, while this study evaluated vaccine effectiveness against infection, including infections that did not result in symptoms.
The MMWR report link along with some excerpts. Follow the link to read the report in its entirety.
Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers — Eight U.S. Locations, December 2020–March 2021
Early Release / March 29, 2021 / 70
Mark G. Thompson, PhD1; Jefferey L. Burgess, MD2; Allison L. Naleway, PhD3; Harmony L. Tyner, MD4; Sarang K. Yoon, DO5; Jennifer Meece, PhD6; Lauren E.W. Olsho, PhD7; Alberto J. Caban-Martinez, DO8; Ashley Fowlkes, ScD1; Karen Lutrick, PhD2; Jennifer L. Kuntz, PhD3; Kayan Dunnigan, MPH9; Marilyn J. Odean, MS10; Kurt T. Hegmann, MD5; Elisha Stefanski6; Laura J. Edwards, MPH7; Natasha Schaefer-Solle, PhD8; Lauren Grant, MS1; Katherine Ellingson, PhD2; Holly C. Groom, MPH3; Tnelda Zunie9; Matthew S. Thiese, PhD5; Lynn Ivacic6; Meredith G. Wesley, MPH7; Julie Mayo Lamberte, MSPH1; Xiaoxiao Sun, PhD2; Michael E. Smith9; Andrew L. Phillips, MD5; Kimberly D. Groover, PhD7; Young M. Yoo, MSPH1; Joe Gerald, MD2; Rachel T. Brown, PhD5; Meghan K. Herring, MPH7; Gregory Joseph, MPH1; Shawn Beitel, MSc2; Tyler C. Morrill, MS7; Josephine Mak, MPH1; Patrick Rivers, MPP2; Katherine M. Harris, PhD7; Danielle R. Hunt, PhD7; Melissa L. Arvay, PhD1; Preeta Kutty, MD1; Alicia M. Fry, MD1; Manjusha Gaglani, MBBS9,11 (View author affiliations)View suggested citation
Summary
What is already known about this topic?
Messenger RNA (mRNA) COVID-19 vaccines have been shown to be effective in preventing symptomatic SARS-CoV-2 infection in randomized placebo-controlled Phase III trials.What is added by this report?Prospective cohorts of 3,950 health care personnel, first responders, and other essential and frontline workers completed weekly SARS-CoV-2 testing for 13 consecutive weeks. Under real-world conditions, mRNA vaccine effectiveness of full immunization (≥14 days after second dose) was 90% against SARS-CoV-2 infections regardless of symptom status; vaccine effectiveness of partial immunization (≥14 days after first dose but before second dose) was 80%.What are the implications for public health practice?Authorized mRNA COVID-19 vaccines are effective for preventing SARS-CoV-2 infection in real-world conditions. COVID-19 vaccination is recommended for all eligible persons.
(SNIP)
Discussion
Prospective cohorts of health care personnel, first responders, and other essential and frontline workers over 13 weeks in eight U.S. locations confirmed that authorized mRNA COVID-19 vaccines (Pfizer-BioNTech’s BNT162b2 and Moderna’s mRNA-1273) are highly effective in real-world conditions. Vaccine effectiveness of full immunization with two doses of mRNA vaccines was 90% (95% CI = 68%–97%) against RT-PCR–confirmed SARS-CoV-2 infection. These findings are consistent with those from the mRNA vaccines’ Phase III trials (1,2) and recent observational studies of the mRNA vaccine effectiveness against severe COVID-19 (3). The findings complement and expand upon these preceding reports by demonstrating that the vaccines can also reduce the risk for infection regardless of COVID-19–associated illness symptom status (4,5). Reducing the risk for transmissible infection, which can occur among persons with asymptomatic infection or among persons several days before symptoms onset (6), is especially important among health care personnel, first responders, and other essential and frontline workers given their potential to transmit the virus through frequent close contact with patients and the public.
Partial immunization (≥14 days after first dose but before second dose) provided preventive benefits with vaccine effectiveness of 80%. This finding is similar to an analysis of Phase III trial results (1,2,7) and two other recent estimates of vaccine effectiveness for partial immunization with Pfizer-BioNTech vaccine among health care personnel, including a vaccine effectiveness (≥21 days after first dose) of 72% (95% CI = 58%–86%) against PCR-confirmed infection identified by routine testing in the United Kingdom (4) and a vaccine effectiveness (>14 days after first dose) of 60% (95% CI = 38%–74%) against PCR-confirmed infection identified by records review in Israel (5). This finding is also consistent with early descriptive findings of SARS-CoV-2 employee and clinical testing results by mRNA vaccination status in the United States (8,9).
The findings in this report are subject to at least three limitations. First, vaccine effectiveness point estimates should be interpreted with caution given the moderately wide CIs attributable in part to the limited number of postimmunization PCR-confirmed infections observed. Second, this also precluded making product-specific vaccine effectiveness estimates and limited the ability to adjust for potential confounders; however, effects were largely unchanged when study site was included in an adjusted vaccine effectiveness model and when adjusted for sex, age, ethnicity, and occupation separately in sensitivity analyses. Finally, self-collection of specimens and delays in shipments could reduce sensitivity of virus detection by PCR (10); if this disproportionately affected those who received the vaccine (e.g., because of possible vaccine attenuation of virus shedding), vaccine effectiveness would be overestimated.
The scientific rigor of these findings is enhanced by its prospective design and the participants’ very high adherence to weekly specimen collection. As the study progresses, viruses will be genetically characterized to examine the viral features of breakthrough infections. Given that there is uncertainty related to the number of days required to develop immunity postvaccination (3–5,7), future research examining vaccine effectiveness at different intervals is warranted.
These interim vaccine effectiveness findings for both Pfizer-BioNTech’s and Moderna’s mRNA vaccines in real-world conditions complement and expand upon the vaccine effectiveness estimates from other recent studies (3–5) and demonstrate that current vaccination efforts are resulting in substantial preventive benefits among working-age adults. They reinforce CDC’s recommendation of full 2-dose immunization with mRNA vaccines. COVID-19 vaccination is recommended for all eligible persons, which currently varies by location in the United States.
While these vaccines should help to substantially reduce the impact of the next pandemic wave in the United States, most of the world's population remains unvaccinated, and that provides the virus ample opportunities to spread, evolve, and potentially learn to evade our current generation of vaccines.
Meaning that while the news on these vaccines is exceedingly good, it is too soon to start popping the champagne corks and declaring victory over the pandemic.
