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COVID mRNA Vaccine Linked 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 pre-procedural tests from December 17, 2020 to February 8, 2021.
Forty-two (1.4%) of 3,006 tests from patients who had received at least one dose of vaccine tested positive for COVID-19, compared with 1,463 (3.2%) of 45,327 tests from unvaccinated patients (relative risk [RR], 0.44).
Compared with unvaccinated patients, the risk of asymptomatic COVID-19 was lower among those who had received a dose of the vaccine at least 10 days before the test (72% reduction; RR, 0.21) and those who received a second dose (73%; RR, 0.20). But after adjusting 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 vaccines in reducing asymptomatic infections that complement the results of the randomized trial in symptomatic patients,” the researchers wrote. “From a public health perspective, it will be important to determine whether current recommendations to maintain pre-vaccination behaviors for masking and social distancing will affect vaccinations.”
March 10th Clin Infect Dis study
Age increase associated with symptomatic COVID-19 after close contact
A new study conducted in the worst-hit region of Italy at the start of the pandemic shows that children and young adults developed symptoms at a much lower rate than older case contacts after exposure to a COVID-19 case. The study was published yesterday in Open JAMA network.
The findings were based on 5,484 close contacts in quarantine from confirmed cases in the Lombardy region. Half of the close contacts (2824, or 51.5%) tested positive for COVID-19, but the majority did not develop respiratory symptoms or fever: only 26.1% (95% CI, 24.1% -28 2%) of infected people younger than 60 years old 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 illness.
Only 18.1% of case contacts younger than 20 years of age developed symptoms, compared with 64.6% of case contacts older than 80 years. The authors also found some difference between close male and female contacts.
“No significant differences were found between male and female patients infected with SARS-CoV-2 in the risk of developing symptoms, while women had 52.7% (95% CI, 24.4-70.7 ) less likely to experience critical illness than men, “the authors wrote.
March 10th JAMA Netw Open study
A study highlights the spread of COVID in hospitals despite the use of masks and glasses
Harvard University scientists detail three cases of COVID-19 spread despite the use of medical masks and eye protection in a study conducted today in Clinical infectious diseases.
The Massachusetts Department of Public Health sequenced the genomes of SARS-CoV-2 samples from patients and employees of Brigham and Women’s Hospital in which spread occurred despite one or both parties wearing ASTM Level 1 masks with earmuffs. These masks are designed to filter out 95% of bacteria and 0.1 micron particles.
Three cases of viral transmission despite the use of masks occurred from November 2020 to mid-January 2021, as determined by the matching virus genomes. The first involved an 82-year-old asymptomatic and unmasked 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 day 3 of hospitalization and the other saw the patient for 8 hours on day 4.
The second case involved the spread of a presymptomatic masked nurse wearing eye protection to a 56-year-old patient without a mask. The nurse developed symptoms of COVID-19 on day 13 of hospitalization from a contact with the community after having treated the patient on days 11-13.
The third case involved the spread of a masked presymptomatic patient to a physician wearing a mask and goggles during a 45-minute encounter at a distance of approximately 3 feet. The patient developed coronavirus symptoms and tested positive 2 days later, as did the doctor on day 4.
The COVID-19 strains involved in the three cases were different from each other and were not variants of concern.
The authors noted that SARS-CoV-2 spreads primarily through small respiratory particles that enter the spaces between masks and faces, particularly during close contact for a long time early in the course of infection. They added that masks can reduce the risk of infection but do not eliminate it.
“These findings teach the importance of not relying solely on medical masks and eye protection to prevent transmission of SARS-CoV-2 and raise the question of whether respirators should be used more widely when caring for high-risk patients under conditions high-risk in high-incidence communities, “the researchers concluded.
March 11th Clin Infect Dis study
