ABSTRACT
Background. From March 2020 through May 2021, Dallas County reported a total of 304,056 cases of COVID-19, including 4,073 deaths. During the month of December 2020, a post-holiday surge of cases led to peak daily average case rates of over 50 cases per 100,000. COVID-19 cases and deaths have since declined substantially following the rollout of COVID-19 vaccine delivery. As of June 8, 2021, about 1,831,588 Dallas County residents have received at least one COVID-19 vaccine dose and 910,067 are fully vaccinated. Recent county integration of immunization and case databases enabled identification and analysis of COVID-19 breakthrough infections. Methods. A COVID-19 breakthrough infection was defined as a positive test (PCR or antigen) collected from an individual ≥ 14 days after receiving the full series of an FDA-authorized COVID-19 vaccine. Nationally, 10,262 vaccine breakthrough infections had been reported from 46 US states and territories, through April 2021. Vaccine breakthrough cases were reviewed and medical records ed to collect demographic information, clinical characteristics, and medical conditions. Data analysis was performed using R, version 4.0.2 (2020). Results. Of the 700 vaccine breakthrough cases reported in Dallas County residents as of June 8, 2021, 304 (43%) were male and 396 (57%) female, with an average age of 53 years. The majority of the vaccine breakthrough cases were White (42%);25% were Hispanic/Latino;and 20% were Black. Almost all breakthrough cases were confirmed with PCR testing, with 451 (64%) cases receiving the Pfizer vaccine. Of breakthrough cases, 49% were symptomatic;52% (358) had underlying conditions including: tobacco use, obesity, or immunocompromised state;68 (10%) were hospitalized;and 11 (1.6%) died. Whole genome sequencing was performed on 51 cases, with 14 (27.5%) variants identified, including: eight B.1.1.7, two B.1.429 and one P.1 variants. Conclusion. Despite the high levels of vaccine efficacy documented in US vaccine trials, COVID-19 breakthrough infections, though currently uncommon, do occur and are important to investigate. Ongoing close public health surveillance of variants is needed to discern changes in patterns of vaccine efficacy and characteristics of populations at greatest risk of severe disease from COVID-19.
ABSTRACT
Background. During 2020, a total of 193,318 cases of COVID-19 were reported in Dallas, with daily average case rates exceeding 50 per 100,000 for over 7 weeks. An adaptable survey functionality within a newly implemented COVID-19 surveillance system provided an opportunity to assess case knowledge and attitudes about isolation and contact tracing efforts. Methods. COVID-19 illnesses were classified using the 2020 CSTE case definitions. Cases were interviewed and records reviewed for exposures and illness characteristics. Supplemental questionnaires assessing knowledge of public health recommendations were given to a convenience sample of 987 cases during the month of December 2020. Fishers exact and chi-square analyses were performed using SAS 9.4. Results. Of the 987 respondents, 99% reported beginning isolation on or before receipt of test results, and 1% were not in isolation at the time of public health interview. Of cases reporting contacts, 92% had advised household members to quarantine prior to interview, and 91% did not want public health to call their household. Of cases reporting non-household close contacts, 75% had advised these contacts to quarantine prior to interview, and 91.3% did not want the health department to call these persons. Cases ≥ 65 years were less likely to have notified their own close contacts (OR: 0.2;95% CI=0.1-0.8) of their test results, and more likely to prefer the health department to notify their household contacts of their positive result (OR: 4.1;95% CI=1.3-12.5). Compared with White cases, Hispanic cases were less likely to be aware that their test was positive at the time of interview (OR: 0.3;95% CI=0.1-0.7). Non-White cases were less likely to be aware of resources for food, rent and utility assistance prior to interview (OR: 0.25;95% CI=0.1-0.7). All respondents perceived the public health interview to have been of some value to them, most often to answer their questions about retesting (51%) and duration of isolation (48%). Conclusion. The aversion of a majority of COVID-19 cases for health department notification of their contacts is a significant deterrent to name-based contact tracing approaches. Acknowledgement of this limitation could better focus existing resources on the delivery of expedited notifications and information to contacts by proxy.