Background The purpose of this study was to evaluate the necessity of COVID-19 vaccination in persons with prior COVID-19. Methods Employees of Cleveland Clinic working in Ohio on Dec 16, 2020, the day COVID-19 vaccination was started, were included. Anyone who tested positive for COVID-19 at least once before the study start date was considered previously infected. One was considered vaccinated 14 days after receiving the second dose of a COVID-19 mRNA vaccine. The cumulative incidence of COVID-19, symptomatic COVID-19, and hospitalizations for COVID-19, were examined over the next year. Results Among 52238 employees, 4718 (9%) were previously infected, and 36922 (71%) were vaccinated by the study’s end. Cumulative incidence of COVID-19 was substantially higher throughout for those previously uninfected who remained unvaccinated than for all other groups, lower for the vaccinated than unvaccinated, and lower for those previously infected than those not. Incidence of COVID-19 increased dramatically in all groups after the Omicron variant emerged. In multivariable Cox proportional hazards regression, both prior COVID-19 and vaccination were independently associated with significantly lower risk of COVID-19. Among previously infected subjects, a lower risk of COVID-19 overall was not demonstrated, but vaccination was associated with a significantly lower risk of symptomatic COVID-19 in both the pre-Omicron (HR 0.60, 95% CI 0.40–0.90) and Omicron (HR 0.36, 95% CI 0.23–0.57) phases. Conclusions Both previous infection and vaccination provide substantial protection against COVID-19. Vaccination of previously infected individuals does not provide additional protection against COVID-19 for several months, but after that provides significant protection at least against symptomatic COVID-19.

A search of radar mosaics and level-II Weather Surveillance Radar-1988 Doppler (WSR-88D) data revealed 51 cold-season (October–April) bow echoes that occurred in the contiguous United States from 1997–98 to 2000–01. Proximity soundings indicated mean 0–2.5-, 0–5-, and 5–10-km shear values of 14, 23, and 19 m s−1, respectively. Mean CAPE was 1366 J kg−1. Most bow echoes developed from squall lines, groups of cells, or squall lines overtaking cells that originated in the path of the squall line. Overall, cell mergers occurred just prior to the development of 34 (67%) of the 51 bow echoes, and embedded supercells were present in the mature stage of 22 (43%) bow echoes. Nine severe, long-lived bow echoes (LBEs) were identified, and seven of these had damage paths that met derecho criteria. LBEs developed in strongly forced, dynamic synoptic patterns with low to moderate instability. As in previous observational studies, proximity soundings suggested that LBEs are possible within much wider ranges of sampled CAPE and shear than idealized numerical modeling studies have indicated. Cold-season bow echoes formed overwhelmingly (47 of 51) in southwesterly 500-mb flow. Twenty (39%) bow echoes formed in a Gulf coast synoptic pattern that produced strong shear and moderate instability over the southeastern United States. Nineteen (37%) and seven (14%) bow echoes, respectively, formed in the plains and east synoptic patterns, which resemble classic severe weather outbreak patterns. Four (8%) bow echoes developed in a northwest flow synoptic pattern that produced strong shear and moderate instability over the southern plains.

Background. The purpose of this study was to evaluate the necessity of COVID-19 vaccination in persons previously infected with SARS-CoV-2. Methods. Employees of the Cleveland Clinic Health System working in Ohio on Dec 16, 2020, the day COVID-19 vaccination was started, were included. Any subject who tested positive for SARS-CoV-2 at least 42 days earlier was considered previously infected. One was considered vaccinated 14 days after receipt of the second dose of a SARS-CoV-2 mRNA vaccine. The cumulative incidence of SARS-CoV-2 infection over the next five months, among previously infected subjects who received the vaccine, was compared with those of previously infected subjects who remained unvaccinated, previously uninfected subjects who received the vaccine, and previously uninfected subjects who remained unvaccinated. Results. Among the 52238 included employees, 1359 (53%) of 2579 previously infected subjects remained unvaccinated, compared with 22777 (41%) of 49659 not previously infected. The cumulative incidence of SARS-CoV-2 infection remained almost zero among previously infected unvaccinated subjects, previously infected subjects who were vaccinated, and previously uninfected subjects who were vaccinated, compared with a steady increase in cumulative incidence among previously uninfected subjects who remained unvaccinated. Not one of the 1359 previously infected subjects who remained unvaccinated had a SARS-CoV-2 infection over the duration of the study. In a Cox proportional hazards regression model, after adjusting for the phase of the epidemic, vaccination was associated with a significantly lower risk of SARS-CoV-2 infection among those not previously infected (HR 0.031, 95% CI 0.015 to 0.061) but not among those previously infected (HR 0.313, 95% CI 0 to Infinity). Conclusions. Individuals who have had SARS-CoV-2 infection are unlikely to benefit from COVID-19 vaccination, and vaccines can be safely prioritized to those who have not been infected before.