August 23, 2021

Clinical Reports

Shedding of Infectious SARS-CoV-2 Despite Vaccination when the Delta Variant is Prevalent - Wisconsin, July 2021
The SARS-CoV-2 Delta variant and its sublineages (B.1.617.2, AY.1, AY.2, AY.3; [1]) can cause high viral loads, are highly transmissible, and contain mutations that confer partial immune escape [2,3]. Using PCR threshold cycle (Ct) data from a single large contract laboratory, authors show that individuals in Wisconsin, USA had similar viral RNA loads in nasal swabs, irrespective of vaccine status, during a time of high and increasing prevalence of the Delta variant. Infectious SARS-CoV-2 was isolated from 51 of 55 specimens (93%) with Ct <25 from both vaccinated and unvaccinated persons, indicating that most individuals with Ct values in this range (Wilson 95% CI 83%-97%) shed infectious virus regardless of vaccine status. Notably, 68% of individuals infected despite vaccination tested positive with Ct <25, including at least 8 who were asymptomatic at the time of testing. Our data substantiate the idea that vaccinated individuals who become infected with the Delta variant may have the potential to transmit SARS-CoV-2 to others. Vaccinated individuals should continue to wear face coverings in indoor and congregate settings, while also being tested for SARS-CoV-2 if they are exposed or experience COVID-like symptoms.

Antiviral Therapeutics and Vaccines

Coronavirus (COVID-19) Update: FDA Authorizes Additional Vaccine Dose for Certain Immunocompromised Individuals
Today, the U.S. Food and Drug Administration amended the emergency use authorizations (EUAs) for both the Pfizer-BioNTech COVID-19 Vaccine and the Moderna COVID-19 Vaccine to allow for the use of an additional dose in certain immunocompromised individuals, specifically, solid organ transplant recipients or those who are diagnosed with conditions that are considered to have an equivalent level of immunocompromise. The Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices is scheduled to meet Friday to discuss further clinical recommendations regarding immunocompromised individuals. Today’s action does not apply to people who are not immunocompromised.

Governor Cuomo Announces COVID-19 Vaccination Mandate for Healthcare Workers
Governor Andrew M. Cuomo announced today that all healthcare workers in New York State, including staff at hospitals and long-term care facilities (LTCF), including nursing homes, adult care, and other congregate care settings, will be required to be vaccinated against COVID-19 by Monday, September 27. The State Department of Health will issue Section 16 Orders requiring all hospitals, LTCF, and nursing homes to develop and implement a policy mandating employee vaccinations, with limited exceptions for those with religious or medical reasons. To date, 75% of the state's ~450,000 hospital workers, 74% of its ~30,000 adult care facility workers, and 68% of its ~145,500 nursing home workers have completed their vaccine series. Lt. Governor Kathy Hochul's administration was briefed before the announcement.

Full vaccination suppresses SARS-CoV-2 delta variant mutation frequency
This study presents the first evidence that full vaccination against COVID-19 suppresses emergent mutations of SARS-CoV-2 delta variants. Tajima’s D test with a threshold value of -2.50, an evolution algorithm can provide a promising tool to forecast new COVID-19 outbreaks.  It remains unclear how human interventions (vaccinations, lockdowns, etc.) affect viral mutation or generate selection pressure of SARS-CoV-2. It has also been obscure if there are differences in various geographic populations. The vaccination coverage rate is inversely correlated to the mutation frequency of the SARS-CoV-2 delta variants in 16 countries of 20 countries studied. Authors also discovered delta variants evolved differently under the positive selection pressure in the United Kingdom and India. Full vaccination against COVID-19 is critical to suppress emergent mutations. Tajima’s D test score, with a threshold value of -2.50, can provide a promising tool to forecast new COVID-19 outbreaks.

Effectiveness of Pfizer-BioNTech and Moderna Vaccines in Preventing SARS-CoV-2 Infection Among Nursing Home Residents Before and During Widespread Circulation of the SARS-CoV-2 B.1.617.2 (Delta) Variant — National Healthcare Safety Network, March 1–August
Early observational studies among nursing home residents showed mRNA vaccines to be 53% to 92% effective against SARS-CoV-2 infection. Two doses of mRNA vaccines were 74.7% effective against infection among nursing home residents early in the vaccination program (March–May 2021). During June–July 2021, when B.1.617.2 (Delta) variant circulation predominated, effectiveness declined significantly to 53.1%. Multicomponent COVID-19 prevention strategies are critical, including vaccination of nursing home staff members, residents, and visitors. An additional dose of the COVID-19 vaccine might be considered for nursing home and long-term care facility residents to optimize a protective immune response.

New COVID-19 Cases and Hospitalizations Among Adults, by Vaccination Status — New York, May 3–July 25, 2021
In the United States, there are limited real-world studies of population-level vaccine effectiveness against laboratory-confirmed SARS-CoV-2 infection and COVID-19 hospitalizations. From May 3–July 25, 2021, the overall age-adjusted vaccine effectiveness against hospitalization in New York was relatively stable (91.9%–95.3%). The overall age-adjusted vaccine effectiveness against infection for all New York adults declined from 91.7% to 79.8%. These findings support the implementation of a multicomponent approach to controlling the pandemic, centered on vaccination, and other prevention strategies such as masking and physical distancing.

Sustained Effectiveness of Pfizer-BioNTech and Moderna Vaccines Against COVID-19 Associated Hospitalizations Among Adults — United States, March–July 2021
COVID-19 mRNA vaccines provide strong protection against severe COVID-19; however, the duration of protection is uncertain. Among 1,129 patients who received 2 doses of an mRNA vaccine, no decline in vaccine effectiveness against COVID-19 hospitalization was observed over 24 weeks. Vaccine effectiveness was 86% 2–12 weeks after vaccination and 84% at 13–24 weeks. Vaccine effectiveness was sustained among groups at risk for severe COVID-19. mRNA vaccine effectiveness against COVID-19–associated hospitalizations was sustained over 24 weeks; ongoing monitoring is needed as new SARS-CoV-2 variants emerge. To reduce hospitalization, all eligible persons should be offered COVID-19 vaccination.

Early Convalescent Plasma for High-Risk Outpatients with Covid-19
Early administration of convalescent plasma obtained from blood donors who have recovered from coronavirus disease 2019 (Covid-19) may prevent disease progression in acutely ill, high-risk patients with Covid-19. In this randomized, multicenter, single-blind trial, authors assigned patients who were being treated in an emergency department for Covid-19 symptoms to receive either one unit of convalescent plasma with a high titer of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or placebo. All the patients were either 50 years of age or older or had one or more risk factors for disease progression. In addition, all the patients presented to the emergency department within 7 days after symptom onset and were in stable condition for outpatient management. The primary outcome was disease progression within 15 days after randomization, which was a composite of hospital admission for any reason, seeking emergency or urgent care, or death without hospitalization. Secondary outcomes included the worst severity of illness on an 8-category ordinal scale, hospital-free days within 30 days after randomization, and death from any cause. A total of 511 patients were enrolled in the trial (257 in the convalescent-plasma group and 254 in the placebo group). The median age of the patients was 54 years; the median symptom duration was 4 days. In the donor plasma samples, the median titer of SARS-CoV-2 neutralizing antibodies was 1:641. Disease progression occurred in 77 patients (30.0%) in the convalescent-plasma group and 81 patients (31.9%) in the placebo group (risk difference, 1.9 percentage points; 95% credible interval, −6.0 to 9.8; posterior probability of superiority of convalescent plasma, 0.68). Five patients in the plasma group and 1 patient in the placebo group died. Outcomes regarding worst illness severity and hospital-free days were similar in the two groups. The administration of Covid-19 convalescent plasma to high-risk outpatients within 1 week after the onset of symptoms of Covid-19 did not prevent disease progression. 


Use of rapid antigen testing for SARS-CoV-2 in remote communities – Yukon-Kuskoswin Delta Region, Alaska, September 15, 2020-March 1, 2021
Until the widespread availability of rapid point-of-care COVID-19 testing, one of the primary challenges in rural Alaska was slow turnaround times for SARS-CoV-2 laboratory-based nucleic acid amplification test results. The introduction of rapid, point-of-care antigen testing in Alaska’s remote Yukon-Kuskokwim Delta region was followed by a more than threefold reduction in daily SARS-CoV-2 case rates during approximately 1 month before the introduction of COVID-19 vaccination. Rapid point-of-care antigen testing shortens the turn-around time and might be a valuable tool in reducing transmission of SARS-CoV-2 in rural communities by facilitating rapid isolation and quarantine.


Association of Age and Pediatric Household Transmission of SARS-CoV-2 Infection
As a result of the low numbers of pediatric cases early in the COVID-19 pandemic, the pediatric household transmission of SARS-CoV-2 remains an understudied topic. The objective of this study was to determine whether there are differences in the odds of household transmission by younger children compared with older children.  This population-based cohort study took place between June 1 and December 31, 2020, in Ontario, Canada. Private households in which the index case individual of laboratory-confirmed SARS-CoV-2 infection was younger than 18 years were included. Individuals were excluded if they resided in apartments missing suite information, in households with multiple index cases, or in households where the age of the index case individual was missing.  The age group of pediatric index cases is categorized as 0 to 3, 4 to 8, 9 to 13, and 14 to 17 years. Household transmission, defined as households where at least 1 secondary case occurred 1 to 14 days after the pediatric index case. A total of 6280 households had pediatric index cases, and 1717 households (27.3%) experienced secondary transmission. The mean (SD) age of pediatric index case individuals was 10.7 (5.1) years and 2863 (45.6%) were female individuals. Children aged 0 to 3 years had the highest odds of transmitting SARS-CoV-2 to household contacts compared with children aged 14 to 17 years (odds ratio, 1.43; 95% CI, 1.17-1.75). This association was similarly observed in sensitivity analyses defining secondary cases as 2 to 14 days or 4 to 14 days after the index case and stratified analyses by the presence of symptoms, association with a school/childcare outbreak, or school/childcare reopening. Children aged 4 to 8 years and 9 to 13 years also had increased odds of transmission (aged 4-8 years: odds ratio, 1.40; 95% CI, 1.18-1.67; aged 9-13 years: odds ratio, 1.13; 95% CI, 0.97-1.32). This study suggests that younger children may be more likely to transmit SARS-CoV-2 infection compared with older children, and the highest odds of transmission were observed for children aged 0 to 3 years. Differential infectivity of pediatric age groups has implications for infection prevention within households, as well as schools/childcare, to minimize the risk of household secondary transmission. Additional population-based studies are required to establish the risk of transmission by younger pediatric index cases.

Situation Dashboards


World Health Organization (WHO)

Novel Coronavirus (COVID-19) Situation from World Health Organization (WHO)

Johns Hopkins University (JHU)

Coronavirus COVID-19 Global Cases by the Center for Systems Science and Engineering (CSSE) at JHU

COVID-19 in US and Canada

1Point3Acres Real-Time Coronavirus (COVID-19) Updates in US and Canada with Credible Sources

Genomic Epidemiology COVID-19

Genomic Epidemiology of (COVID-19) Maintained by the Nextstrain team, enabled by data from GISAID.

Sources for COVID-19 Information


World Health Organization (WHO)


Centers for Disease Control, US


International Society for Infectious Diseases


This Week in Virology (TWIV)

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