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mRNA COVID vaccination tied to 80% lower risk of asymptomatic infection
A real-world Mayo Clinic study shows a link between vaccination with two doses of an mRNA-based COVID-19 vaccine—either Pfizer/BioNTech or Moderna—and an 80% lower risk of asymptomatic infection.
The retrospective cohort study, published yesterday in Clinical Infectious Diseases, involved 39,156 asymptomatic adult COVID-19 patients screened for SARS-CoV-2 infection using 48,333 preprocedural tests from Dec 17, 2020, to Feb 8, 2021.
Forty-two (1.4%) of 3,006 tests of patients who had received at least one dose of vaccine were positive for COVID-19, compared with 1,463 (3.2%) of 45,327 tests of unvaccinated patients (relative risk [RR], 0.44).
Compared with unvaccinated patients, the risk of asymptomatic COVID-19 was lower among those who had received one dose of vaccine at least 10 days before testing (72% reduction; RR, 0.21) and those who received a second dose (73%; RR, 0.20). But after adjustment for confounding factors, the risk of infection was 80% lower in those who received two doses.
“The results of this study demonstrate the impact of the vaccines on reduction in asymptomatic infections supplementing the randomized trial results on symptomatic patients,” the researchers wrote. “From a public health perspective, it will be important to determine if the current recommendations to maintain pre-vaccination behaviors for masking and social distancing will impact vaccine hesitancy.”
Mar 10 Clin Infect Dis study
Increasing age associated with symptomatic COVID-19 after close contact
A new study out of Italy’s hardest-hit region early in the pandemic shows that children and young adults developed symptoms at a far lesser rate than older case contacts after exposure to a COVID-19 case. The study was published yesterday in JAMA Network Open.
The findings were based on 5,484 quarantined close contacts of confirmed cases in the Lombardy region. Half of the close contacts (2,824, or 51.5%) tested positive for COVID-19, but most did not develop respiratory symptoms or fever: Only 26.1% (95% CI, 24.1%-28.2%) of infected individuals younger than 60 years developed respiratory symptoms or fever, the authors wrote. Among infected participants older than 60 years, 6.6% (95% CI, 5.1%-8.3%) developed critical disease.
Only 18.1% of case contacts under the age of 20 developed symptoms, compared with 64.6% of case contacts over the age of 80. The authors also found some difference between male and female close contacts.
“No significant differences between SARS-CoV-2–infected female and male patients were found in the risk of developing symptoms, whereas female patients were 52.7% (95% CI, 24.4-70.7) less likely to experience critical disease than male patients,” the authors wrote.
Mar 10 JAMA Netw Open study
Study highlights COVID spread in hospitals despite use of masks, goggles
Harvard University scientists detail three cases of COVID-19 spread despite the use of medical masks and eye protection in a study today in Clinical Infectious Diseases.
The Massachusetts Department of Public Health sequenced the genomes of SARS-CoV-2 specimens from patients and employees at Brigham and Women’s Hospital in which spread occurred despite one or both parties wearing ASTM Level 1 masks with ear loops. These masks are designed to filter 95% of bacteria and 0.1-micrometer particles.
Three cases of viral transmission despite use of masks occurred from November 2020 to mid-January 2021, as determined by matching virus genomes. The first involved an asymptomatic, unmasked 82-year-old patient who infected two patient care assistants wearing masks and face shields. Both assistants developed symptoms 4 and 5 days after the patient’s diagnosis. One had spent 4 hours with the patient on hospital day 3, and the other tended to the patient for 8 hours on day 4.
The second case involved spread from a presymptomatic masked nurse wearing eye protection to an unmasked 56-year-old patient. The nurse developed COVID-19 symptoms on hospital day 13 from a community contact after having cared for the patient on days 11 to 13.
The third case involved spread from a presymptomatic masked patient to a physician wearing a mask and goggles during a 45-minute encounter at a distance of about 3 feet. The patient developed coronavirus symptoms and tested positive 2 days later, as did the physician on day 4.
The COVID-19 strains involved in the three cases were different from each other and weren’t variants of concern.
The authors noted that SARS-CoV-2 is primarily spread through tiny respiratory particles that enter the gaps between masks and faces, particularly during close contact over a prolonged time early in the course of infection. They added that masks may lower infection risk but don’t eliminate it.
“These findings teach the importance of not relying on medical masks and eye protection alone to prevent SARS-CoV-2 transmission and beg the question whether respirators should be used more widely when caring for high-risk patients under high-risk conditions in high incidence communities,” the researchers concluded.
Mar 11 Clin Infect Dis study