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Abstract Background Few studies have attempted to use clinical and laboratory parameters to stratify COVID-19 patients with severe versus non-severe initial disease and evaluate age-specific differences in developing multiple different COVID-19-associated disease outcomes. Methods A retrospective cohort included patients from the electronic health database of Hong Kong Hospital Authority between 1 January 2022 and 15 August 2022 until 15 November 2022. The cohort was divided into three cohorts by age (≤ 40, 41–64, and ≥ 65 years old). Each age cohort was stratified into four groups: (1) COVID-19 critically exposed group (ICU admission, mechanical ventilation support, CRP > 80 mg/L, or D-dimer > 2 g/mL), (2) severely exposed group (CRP 30–80 mg/L, D-dimer 0.5–2 g/mL, or CT value 40) for the disease outcomes in the acute phase of infection (e.g., mortality risk HR (aged ≤ 40): 1.0 (95%CI: 0.5,2.0), HR (aged 41–64): 2.1 (95%CI: 1.8, 2.6), HR (aged > 65): 4.8 (95%CI: 4.6, 5.1)); while in the post-acute phase, these risks were largely insignificant in those aged 65): 1.5 (95%CI: 1.5,1.6)). Fully vaccinated patients were associated with lower risks of disease outcomes than those receiving less than two doses of vaccination. Conclusions The risk of multiple different disease outcomes in both acute and post-acute phases increased significantly with the increasing severity of acute COVID-19 illness, specifically among the elderly. Moreover, future studies could improve by risk-stratifying patients based on universally accepted thresholds for clinical parameters, particularly biomarkers, using biological evidence from immunological studies.

Abstract Background In view of accumulating case reports of thyroid dysfunction following COVID-19 vaccination, we evaluated the risks of incident thyroid dysfunction following inactivated (CoronaVac) and mRNA (BNT162b2) COVID-19 vaccines using a population-based dataset. Methods We identified people who received COVID-19 vaccination between 23 February and 30 September 2021 from a population-based electronic health database in Hong Kong, linked to vaccination records. Thyroid dysfunction encompassed anti-thyroid drug (ATD)/levothyroxine (LT4) initiation, biochemical picture of hyperthyroidism/hypothyroidism, incident Graves’ disease (GD), and thyroiditis. A self-controlled case series design was used to estimate the incidence rate ratio (IRR) of thyroid dysfunction in a 56-day post-vaccination period compared to the baseline period (non-exposure period) using conditional Poisson regression. Results A total of 2,288,239 people received at least one dose of COVID-19 vaccination (57.8% BNT162b2 recipients and 42.2% CoronaVac recipients). 94.3% of BNT162b2 recipients and 92.2% of CoronaVac recipients received the second dose. Following the first dose of COVID-19 vaccination, there was no increase in the risks of ATD initiation (BNT162b2: IRR 0.864, 95% CI 0.670–1.114; CoronaVac: IRR 0.707, 95% CI 0.549–0.912), LT4 initiation (BNT162b2: IRR 0.911, 95% CI 0.716–1.159; CoronaVac: IRR 0.778, 95% CI 0.618–0.981), biochemical picture of hyperthyroidism (BNT162b2: IRR 0.872, 95% CI 0.744–1.023; CoronaVac: IRR 0.830, 95% CI 0.713–0.967) or hypothyroidism (BNT162b2: IRR 1.002, 95% CI 0.838–1.199; CoronaVac: IRR 0.963, 95% CI 0.807–1.149), GD, and thyroiditis. Similarly, following the second dose of COVID-19 vaccination, there was no increase in the risks of ATD initiation (BNT162b2: IRR 0.972, 95% CI 0.770–1.227; CoronaVac: IRR 0.879, 95%CI 0.693–1.116), LT4 initiation (BNT162b2: IRR 1.019, 95% CI 0.833–1.246; CoronaVac: IRR 0.768, 95% CI 0.613–0.962), hyperthyroidism (BNT162b2: IRR 1.039, 95% CI 0.899–1.201; CoronaVac: IRR 0.911, 95% CI 0.786–1.055), hypothyroidism (BNT162b2: IRR 0.935, 95% CI 0.794–1.102; CoronaVac: IRR 0.945, 95% CI 0.799–1.119), GD, and thyroiditis. Age- and sex-specific subgroup and sensitivity analyses showed consistent neutral associations between thyroid dysfunction and both types of COVID-19 vaccines. Conclusions Our population-based study showed no evidence of vaccine-related increase in incident hyperthyroidism or hypothyroidism with both BNT162b2 and CoronaVac.

Abstract Background Safety after the second dose of the SARS-CoV-2 vaccine remains to be elucidated, especially among individuals reporting adverse events after their first dose. This study aims to evaluate the impact of a delayed second dose on all-cause mortality and emergency services. Methods A territory-wide, retrospective cohort of people who had completed two doses of mRNA (BNT162b2) or inactivated SARS-CoV-2 (CoronaVac) vaccine between February 23 and July 3, 2021, in Hong Kong was analyzed, with linkage to electronic health records retrieved from the Hong Kong Hospital Authority. Vaccine recipients were classified as receiving a second dose within recommended intervals (21–28 days for BNT162b2; 14–28 days for CoronaVac) or delayed. Study outcomes were all-cause mortality, emergency department (ED) visits, and unscheduled hospitalizations within 28 days after the second dose of vaccination. Results Among 417,497 BNT162b2 and 354,283 CoronaVac second dose recipients, 3.8% and 28.5% received the second dose beyond the recommended intervals (mean 34.4 and 31.8 days), respectively. During the study period, there were < 5 daily new cases of COVID-19 infections in the community. Delaying the second dose was not associated with all-cause mortality (hazard ratio [HR] = 1.185, 95% CI 0.478–2.937, P = 0.714), risk of ED visit (HR = 0.966, 95% CI 0.926–1.008, P = 0.113), and risk of unscheduled hospitalization (HR = 0.956, 95% CI 0.878–1.040, P = 0.294) compared to that within the recommended interval for CoronaVac recipients. No statistically significant differences in all-cause mortality (HR = 4.438, 95% CI 0.951–20.701, P = 0.058), ED visit (HR = 1.037, 95% CI 0.951–1.130, P = 0.411), and unscheduled hospitalization (HR = 1.054, 95% CI 0.867–1.281, P = 0.597) were identified between people who received a second dose of BNT162b2 within and beyond the recommended intervals. Conclusions No significant association between delayed second dose of BNT162b2 or CoronaVac and all-cause mortality, ED visit, and unscheduled hospitalization was observed in the present cohort. Regardless of the recommended or delayed schedule for SARS-CoV-2 vaccination, a second dose of both vaccines should be administered to obtain better protection against infection and serious disease. The second dose should be administered within the recommended interval following the manufacturer’s product information, until further studies support the benefits of delaying vaccination outweighing the risks.

Background Safety monitoring of coronavirus disease 2019 (COVID-19) vaccines is crucial during mass vaccination rollout to inform the choice of vaccines and reduce vaccine hesitancy. Considering the scant evidence directly comparing the safety profiles of mRNA and inactivated SARS-CoV-2 vaccines, this territory-wide cohort study aims to compare the incidence of various adverse events of special interest (AESIs) and all-cause mortality between CoronaVac (inactivated vaccine) and BNT162b2 (mRNA-based vaccine). Our results can help vaccine recipients make an informed choice. Methods and findings A retrospective, population-based cohort of individuals who had received at least 1 dose of BNT162b2 or CoronaVac from 23 February to 9 September 2021 in Hong Kong, and had data linkage to the electronic medical records of the Hong Kong Hospital Authority, were included. Those who had received mixed doses were excluded. Individuals were observed from the date of vaccination (first or second dose) until mortality, second dose vaccination (for first dose analysis), 21 days after vaccination, or 30 September 2021, whichever came first. Baseline characteristics of vaccinated individuals were balanced between groups using propensity score weighting. Outcome events were AESIs and all-cause mortality recorded during 21 days of post-vaccination follow-up after each dose, except anaphylaxis, for which the observation period was restricted to 2 days after each dose. Incidence rate ratios (IRRs) of AESIs and mortality comparing between CoronaVac and BNT162b2 recipients were estimated after each dose using Poisson regression models. Among 2,333,379 vaccinated individuals aged 18 years or above, the first dose analysis included 1,308,820 BNT162b2 and 955,859 CoronaVac recipients, while the second dose analysis included 1,116,677 and 821,560 individuals, respectively. The most frequently reported AESI among CoronaVac and BNT162b2 recipients was thromboembolism (first dose: 431 and 290 per 100,000 person-years; second dose: 385 and 266 per 100,000 person-years). After the first dose, incidence rates of overall AESIs (IRR = 0.98, 95% CI 0.89–1.08, p = 0.703) and mortality (IRR = 0.96, 95% CI 0.63–1.48, p = 0.868) associated with CoronaVac were generally comparable to those for BNT162b2, except for Bell palsy (IRR = 1.95, 95% CI 1.12–3.41, p = 0.018), anaphylaxis (IRR = 0.34, 95% CI 0.14–0.79, p = 0.012), and sleeping disturbance or disorder (IRR = 0.66, 95% CI 0.49–0.89, p = 0.006). After the second dose, incidence rates of overall AESIs (IRR = 0.97, 95% CI 0.87–1.08, p = 0.545) and mortality (IRR = 0.85, 95% CI 0.51–1.40, p = 0.516) were comparable between CoronaVac and BNT162b2 recipients, with no significant differences observed for specific AESIs. The main limitations of this study include residual confounding due to its observational nature, and the possibility of its being underpowered for some AESIs with very low observed incidences. Conclusions In this study, we observed that the incidences of AESIs (cumulative incidence rate of 0.06%–0.09%) and mortality following the first and second doses of CoronaVac and BNT162b2 vaccination were very low. The safety profiles of the vaccines were generally comparable, except for a significantly higher incidence rate of Bell palsy, but lower incidence rates of anaphylaxis and sleeping disturbance or disorder, following first dose CoronaVac versus BNT162b2 vaccination. Our results could help inform the choice of inactivated COVID-19 vaccines, mainly administered in low- and middle-income countries with large populations, in comparison to the safety of mRNA vaccines. Long-term surveillance on the safety profile of COVID-19 vaccines should continue. In a retrospective study, Carlos King Ho Wong, Kristy Tsz Kwan Lau, and colleagues study adverse events reported following COVID-19 vaccination in Hong Kong. Author summary Why was this study done? Various SARS-CoV-2 vaccines have been developed for coronavirus disease 2019 (COVID-19) prevention to reduce the risks of severe disease and death; however, vaccine hesitancy due to fear of adverse reactions remains a barrier to mass uptake. Continuous post-marketing surveillance of vaccine safety is crucial to guide informed decision-making and promote vaccine uptake in the community. There is very limited evidence directly comparing the safety profiles of mRNA-based and inactivated SARS-CoV-2 vaccines. What did the researchers do and find? A territory-wide retrospective cohort study of individuals who had received at least 1 dose of BNT162b2 (mRNA-based vaccine, Comirnaty) or CoronaVac (inactivated SARS-CoV-2 vaccine) from 23 February to 9 September 2021 in Hong Kong was conducted to compare the occurrence of selected adverse events of special interest (AESIs) and all-cause death between recipients of the 2 vaccines during 21 days of follow-up after the first and second doses. The incidence of overall AESIs was very low for both vaccines (cumulative incidence rate of 0.06%–0.09%), and the most frequently reported AESI among CoronaVac and BNT162b2 recipients was thromboembolism (first dose: 431 and 290 per 100,000 person-years; second dose: 385 and 266 per 100,000 person-years). The incidence rates of overall AESIs and all-cause death were comparable between CoronaVac and BNT162b2 recipients after the first and second doses, except for a higher incidence rate of Bell palsy, and lower incidence rates of anaphylaxis and sleeping disturbance or disorder, following first dose CoronaVac versus BNT162b2 vaccination. What do these findings mean? Both vaccines had similarly acceptable safety profiles, and the risks of AESIs and all-cause death following CoronaVac or BNT162b2 vaccination were very low, which adds to the real-world evidence on the safety of both COVID-19 vaccines, and may help reduce vaccine hesitancy by addressing safety concerns. Our results may inform the public about the choice of COVID-19 vaccines, and governments about the allocation of healthcare resources for monitoring specific AESIs during vaccine rollout (especially for Bell palsy among first dose CoronaVac recipients, and anaphylaxis and sleeping disturbance or disorder among first dose BNT162b2 recipients). As currently done for mRNA vaccines, clinical data and observational reports of all COVID-19 vaccines should be made publicly available in a timely manner, and long-term monitoring of their safety profiles should continue.