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Pfizer and Moderna cut COVID-19 infection risk by 91% in the fully vaccinated

mRNA vaccines were highly effective among working-age adults in preventing SARS-CoV-2 infection when administered in real-world conditions, lessening the viral RNA load, risk of febrile symptoms, and duration of illness among those who had breakthrough infection despite vaccination, according to a study in the New England Journal of Medicine.

Researchers say these results are among the first to show that mRNA vaccination benefits even those individuals who experience breakthrough infections.

"One of the unique things about this study is that it measured the secondary benefits of the vaccine," said Sarang Yoon, a study co-author, assistant professor at the University of Utah Rocky Mountain Center for Occupational and Environmental Health (RMCOEH), and principal investigator of the RECOVER (Research on the Epidemiology of SARS-CoV-2 in Essential Response Personnel) study in Utah.

The study builds on preliminary data released by the Centers for Disease Control and Prevention (CDC) in March and was designed to measure the risks and rates of infection among those on the front lines of the pandemic.

"We gave these vaccines to some of the highest risk groups in this country – doctors, nurses, and first responders," Yoon said. "These are the people being exposed to the virus day in and day out, and the vaccine protected them against getting the disease. Those who unfortunately got COVID-19 despite being vaccinated were still better off than those who didn't."

The study found that mRNA COVID-19 vaccines were: 91% effective in reducing risk for infection once participants were "fully" vaccinated, two weeks after the second dose, and  81% effective in reducing risk for infection after "partial" vaccination, two weeks after the first dose but before the second dose was given.

The HEROES-RECOVER network recruited 3,975 participants at eight sites across the country. Participants submitted samples for COVID-19 testing on a weekly basis for 17 weeks between 13 December 2020 and April 10, 2021. They also reported weekly whether they had COVID-19- like symptoms, including fever, shortness of breath, and loss of taste and smell.

Only 204 (5%) of the participants eventually tested positive for SARS- CoV-2, the virus that causes COVID-19. Of these, 156 were unvaccinated, 32 had an indeterminate vaccine status, and 16 were fully or partially vaccinated. The fully or partially vaccinated participants who developed breakthrough had milder symptoms than those who were unvaccinated: presence of fever was reduced 58% among those vaccinated with a breakthrough infection. Days spent sick in bed were reduced by 60% among those who developed a breakthrough infection.

Detection of the virus was reduced by 70%  among those with breakthrough infections, from 8.9 days to 2.7 days. The three people who were hospitalised were not immunised, meaning that no one who developed a breakthrough infection was hospitalised.

These findings also suggest that fully or partially vaccinated individuals who get COVID-19 might be less likely to spread the virus to others. The researchers found that infected study participants who had been fully or partially vaccinated when infected had 40% less detectable virus in the nose and did so for six fewer days compared with those who were unvaccinated.

Overall, the researchers conclude the study's findings support the CDC's recommendation to get fully vaccinated as soon as possible. "I hope these findings reassure the public that mRNA COVID-19 vaccines are safe and protect us from this severe disease," Yoon said.

The RECOVER study is ongoing, and results from future phases will help determine how long COVID-19 vaccines protect against infection and the real-world effectiveness of newer vaccines. A new study will test the same questions in children 12 and older who are eligible to receive the COVID-19 vaccination. The research will also investigate how well COVID-19 vaccines protect against new variants now circulating in the US, including the highly transmissible Delta variant.

Study details

Prevention and Attenuation of Covid-19 with the BNT162b2 and mRNA-1273 Vaccines

Mark G. Thompson, Jefferey L. Burgess, Allison L. Naleway, Harmony Tyner, Sarang K. Yoon, Jennifer Meece, Lauren E.W. Olsho, Alberto J. Caban-Martinez, Ashley L. Fowlkes, Karen Lutrick, Holly C. Groom, Kayan Dunnigan.

Published in New England Journal of Medicine 30 June 2021

Abstract

Background
Information is limited regarding the effectiveness of the two-dose messenger RNA (mRNA) vaccines BNT162b2 (Pfizer–BioNTech) and mRNA-1273 (Moderna) in preventing infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and in attenuating coronavirus disease 2019 (Covid-19) when administered in real-world conditions.

Methods
We conducted a prospective cohort study involving 3975 health care personnel, first responders, and other essential and frontline workers. From 14 December 2020, to 10 April 2021, the participants completed weekly SARS-CoV-2 testing by providing mid-turbinate nasal swabs for qualitative and quantitative reverse-transcriptase–polymerase-chain-reaction (RT-PCR) analysis. The formula for calculating vaccine effectiveness was 100%×(1−hazard ratio for SARS-CoV-2 infection in vaccinated vs. unvaccinated participants), with adjustments for the propensity to be vaccinated, study site, occupation, and local viral circulation.

Results
SARS-CoV-2 was detected in 204 participants (5%), of whom 5 were fully vaccinated (≥14 days after dose 2), 11 partially vaccinated (≥14 days after dose 1 and <14 days after dose 2), and 156 unvaccinated; the 32 participants with indeterminate vaccination status (<14 days after dose 1) were excluded. Adjusted vaccine effectiveness was 91% (95% confidence interval [CI], 76 to 97) with full vaccination and 81% (95% CI, 64 to 90) with partial vaccination. Among participants with SARS-CoV-2 infection, the mean viral RNA load was 40% lower (95% CI, 16 to 57) in partially or fully vaccinated participants than in unvaccinated participants. In addition, the risk of febrile symptoms was 58% lower (relative risk, 0.42; 95% CI, 0.18 to 0.98) and the duration of illness was shorter, with 2.3 fewer days spent sick in bed (95% CI, 0.8 to 3.7).

Conclusions
Authorised mRNA vaccines were highly effective among working-age adults in preventing SARS-CoV-2 infection when administered in real-world conditions, and the vaccines attenuated the viral RNA load, risk of febrile symptoms, and duration of illness among those who had breakthrough infection despite vaccination.
(Funded by the National Center for Immunization and Respiratory Diseases and the Centers for Disease Control and Prevention.)

 

Full New England Journal of Medicine article Prevention and Attenuation of Covid-19 with the BNT162b2 and mRNA-1273 Vaccines (Open access)

 

See more from MedicalBrief archives:

 

Pfizer mRNA vaccine induces persistent human germinal centre responses

 

More data backs high efficacy of single-dose Pfizer jab but Fauci sceptical

 

COVID-19 recoverees may need only a single vaccine dose — Small US study

 

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