Effects of return-to-office, public schools reopening, and vaccination mandates on COVID-19 cases among municipal employee residents of New York City

ObjectiveOn September 13, 2021, teleworking ended for New York City municipal employees, and Department of Education (DOE) employees returned to reopened schools. On October 29, COVID-19 vaccination was mandated. We assessed these mandates short-term effects on disease transmission. MethodsUsing difference-in-difference analyses, we calculated COVID-19 incidence rate ratios (IRR) among residents 18-64 years-old by employment status pre- and post-policy implementation. ResultsIRRs post-(September 23-October 28) vs. pre-(July 5-September 12) return-to-office were similar between office-based City employees and non-City employees. Among DOE employees, the IRR after schools reopened was elevated 28.4% (95% CI: 17.3%-40.3%). Among City employees, the IRR post-(October 29-November 30) vs. pre- (September 23- October 28) vaccination mandate was lowered 20.1% (95% CI: 13.7%-26.0%). ConclusionsWorkforce mandates influenced disease transmission, among other societal effects.

Assessment of COVID-19 hospitalization risk during SARS-CoV-2 Omicron relative to Delta variant predominance, New York City, August 2021-January 2022

ImportanceAssessing relative disease severity of SARS-CoV-2 variants in populations with varied vaccination and infection histories can help characterize emerging variants and support healthcare system preparedness. ObjectiveTo assess COVID-19 hospitalization risk for patients infected with Omicron (BA.1 and sublineages) compared with Delta SARS-CoV-2 variants. DesignObservational cohort study. SettingNew York City Department of Health and Mental Hygiene population-based COVID-19 disease registry, linked with laboratory results, immunization registry, and supplemental hospitalization data sources. ParticipantsNew York City residents with positive laboratory-based SARS-CoV-2 tests during August 2021-January 2022. A secondary analysis restricted to patients with whole-genome sequencing results, comprising 1%-18% of weekly confirmed cases. ExposuresDiagnosis during periods when [≥]98% of sequencing results were Delta (August-November 2021) or Omicron (January 2022). A secondary analysis defined variant exposure using patient-level sequencing results. Main outcomes and measuresCOVID-19 hospitalization, defined as a positive SARS-CoV-2 test 14 days before or 3 days after hospital admission. ResultsAmong 646,852 persons with a positive laboratory-based SARS-CoV-2 test, hospitalization risk was lower for patients diagnosed when Omicron predominated (16,025/488,053, 3.3%) than when Delta predominated (8,268/158,799, 5.2%). In multivariable analysis adjusting for demographic characteristics and prior diagnosis and vaccination status, patients diagnosed when Omicron relative to Delta predominated had 0.72 (95% confidence interval [CI]: 0.63, 0.82) times the hospitalization risk. In a secondary analysis of 55,138 patients with sequencing results, hospitalization risk was similar for patients infected with Omicron (2,042/29,866, 6.8%) relative to Delta (1,780/25,272, 7.0%) and higher among those who received two mRNA vaccine doses (adjusted relative risk 1.64, 95% CI: 1.44, 1.87). Conclusions and relevanceIllness severity was lower for patients diagnosed when Omicron (BA.1 and sublineages) relative to Delta predominated. This finding was consistent after adjusting for prior diagnosis and vaccination status, suggesting intrinsic virologic properties, not population-based immunity, accounted for the lower severity. A secondary analysis demonstrated collider bias from the sequencing sampling frame changing over time in ways associated with disease severity. Investing in representative data collection is necessary to avoid bias in assessing relative disease severity as new variants emerge, immunity wanes, and additional COVID-19 vaccines are administered.

Delays in COVID-19 Diagnosis and Hospitalization and Outcomes -- New York City, New York, USA, October 2020-November 2021

COVID-19 patients diagnosed [≥]3 days after symptom onset had increased odds of hospitalization. The 75th percentile for diagnosis delay was 5 days for residents of low-privilege areas and Black and Hispanic people diagnosed before SARS-CoV-2 Delta predominance, compared with 4 days for other patients, indicating inequities in prompt diagnosis.

Reduced Odds of SARS-CoV-2 Reinfection after Vaccination among New York City Adults, June-August 2021

BackgroundBelief in immunity from prior infection and concern that vaccines might not protect against new variants are contributors to vaccine hesitancy. We assessed effectiveness of full and partial COVID-19 vaccination against reinfection when Delta was the predominant variant in New York City. MethodsWe conducted a case-control study in which case-patients with reinfection during June 15- August 31, 2021 and control subjects with no reinfection were matched (1:3) on age, sex, timing of initial positive test in 2020, and neighborhood poverty level. Conditional logistic regression was used to calculate matched odds ratios (mOR) and 95% confidence intervals (CI). ResultsOf 349,598 adult residents who tested positive for SARS-CoV-2 infection in 2020, did not test positive again >90 days after initial positive test through June 15, 2021, and did not die before June 15, 2021, 1,067 were reinfected during June 15-August 31, 2021. Of 1,048 with complete matching criteria data, 499 (47.6%) were known to be symptomatic for COVID-19-like-illness, and 75 (7.2%) were hospitalized. Unvaccinated individuals, compared with fully vaccinated individuals, had elevated odds of reinfection (mOR, 2.23; 95% CI, 1.90, 2.61), of symptomatic reinfection (mOR, 2.17; 95% CI, 1.72, 2.74), and of reinfection with hospitalization (mOR, 2.59; 95% CI, 1.43, 4.69). Partially versus fully vaccinated individuals had 1.58 (95% CI: 1.22, 2.06) times the odds of reinfection. All three vaccines authorized or approved for use in the U.S. were similarly effective. ConclusionAmong adults with previous SARS-CoV-2 infection, vaccination reduced odds of reinfections when the Delta variant predominated.

Reduced COVID-19 Hospitalizations among New York City Residents Following Age-Based SARS-CoV-2 Vaccine Eligibility: Evidence from a Regression Discontinuity Design

BackgroundIn clinical trials, several SARS-CoV-2 vaccines were shown to reduce risk of severe COVID-19 illness. Local, population-level, real-world evidence of vaccine effectiveness is accumulating. We assessed vaccine effectiveness for community-dwelling New York City (NYC) residents using a quasi-experimental, regression discontinuity design, leveraging a period (January 12-March 9, 2021) when [≥]65-year-olds were vaccine-eligible but younger persons, excluding essential workers, were not. MethodsWe constructed segmented, negative binomial regression models of age-specific COVID-19 hospitalization rates among 45-84-year-old NYC residents during a post-vaccination program implementation period (February 21-April 17, 2021), with a discontinuity at age 65 years. The relationship between age and hospitalization rates in an unvaccinated population was incorporated using a pre-implementation period (December 20, 2020-February 13, 2021). We calculated the rate ratio (RR) and 95% confidence interval (CI) for the interaction between implementation period (pre or post) and age-based eligibility (45-64 or 65-84 years). Analyses were stratified by race/ethnicity and borough of residence. Similar analyses were conducted for COVID-19 deaths. ResultsHospitalization rates among 65-84-year-olds decreased from pre- to post-implementation periods (RR 0.85, 95% CI: 0.74-0.97), controlling for trends among 45-64-year-olds. Accordingly, an estimated 721 (95% CI: 126-1,241) hospitalizations were averted. Residents just above the eligibility threshold (65-66-year-olds) had lower hospitalization rates than those below (63-64-year-olds). Racial/ethnic groups and boroughs with higher vaccine coverage generally experienced greater reductions in RR point estimates. Uncertainty was greater for the decrease in COVID-19 death rates (RR 0.85, 95% CI: 0.66-1.10). ConclusionThe vaccination program in NYC reduced COVID-19 hospitalizations among the initially age-eligible [≥]65-year-old population by approximately 15%. The real-world evidence of vaccine effectiveness makes it more imperative to improve vaccine access and uptake to reduce inequities in COVID-19 outcomes.

Evaluation of Nowcasting for Real-Time COVID-19 Tracking - New York City, March-May 2020

To account for delays between specimen collection and report, the New York City Department of Health and Mental Hygiene used a time-correlated Bayesian nowcasting approach to support real-time COVID-19 situational awareness. We retrospectively evaluated nowcasting performance for case counts among residents diagnosed during March-May 2020, a period when the median reporting delay was 2 days. Nowcasts with a 2-week moving window and a negative binomial distribution had lower mean absolute error, lower relative root mean square error, and higher 95% prediction interval coverage than nowcasts conducted with a 3-week moving window or with a Poisson distribution. Nowcasts conducted toward the end of the week outperformed nowcasts performed earlier in the week, given fewer patients diagnosed on weekends and lack of day-of-week adjustments. When estimating case counts for weekdays only, metrics were similar across days the nowcasts were conducted, with Mondays having the lowest mean absolute error, of 183 cases in the context of an average daily weekday case count of 2,914. Nowcasting ensured that recent decreases in observed case counts were not overinterpreted as true declines and supported health department leadership in anticipating the magnitude and timing of hospitalizations and deaths and allocating resources geographically.

Detecting Emerging COVID-19 Community Outbreaks at High Spatiotemporal Resolution - New York City, June 2020

New York Citys Health Department developed a SARS-CoV-2 percent test positivity cluster detection system using census tract resolution and the SaTScan prospective space-time scan statistic. One cluster led to identifying a gathering with inadequate social distancing where viral transmission likely occurred, and another cluster prompted targeted community testing and outreach.

Estimating the infection fatality risk of COVID-19 in New York City, March 1-May 16, 2020

During March 1-May 16, 2020, 191,392 laboratory-confirmed COVID-19 cases were diagnosed and reported and 20,141 confirmed and probable COVID-19 deaths occurred among New York City (NYC) residents. We applied a network model-inference system developed to support the Citys pandemic response to estimate underlying SARS-CoV-2 infection rates. Based on these estimates, we further estimated the infection fatality risk (IFR) for 5 age groups (i.e. <25, 25-44, 45-64, 65-74, and 75+ years) and all ages overall, during March 1-May 16, 2020. We estimated an overall IFR of 1.45% (95% Credible Interval: 1.09-1.87%) in NYC. In particular, weekly IFR was estimated as high as 6.1% for 65-74 year-olds and 17.0% for 75+ year-olds. These results are based on more complete ascertainment of COVID-19-related deaths in NYC and thus likely more accurately reflect the true, higher burden of death due to COVID-19 than previously reported elsewhere. It is thus crucial that officials account for and closely monitor the infection rate and population health outcomes and enact prompt public health responses accordingly as the pandemic unfolds.