Cases of carditis after the use of a messenger RNA (mRNA) COVID-19 vaccine have been reported in various populations worldwide. However, few studies have directly evaluated this association. Furthermore, it is unclear whether this potential risk involves vaccine platforms other than mRNA vaccines. This case–control study from Hong Kong aimed to examine the association between COVID-19 vaccination with an mRNA vaccine or an inactivated virus vaccine and the subsequent risk for carditis. The results of this study could be useful for public health policymakers to weigh the risk and benefit of population-wide COVID-19 vaccination programs.

ObjectivesTo investigate the relationship between COVID-19 full vaccination (two completed doses) and possible arthritis flare.MethodsPatients with rheumatoid arthritis (RA) were identified from population-based electronic medical records with vaccination linkage and categorised into BNT162b2 (mRNA vaccine), CoronaVac (inactive virus vaccine) and non-vaccinated groups. The risk of possible arthritis flare after vaccination was compared using a propensity-weighted cohort study design. We defined possible arthritis flare as hospitalisation and outpatient consultation related to RA or reactive arthritis, based on diagnosis records during the episode. Weekly prescriptions of rheumatic drugs since the launch of COVID-19 vaccination programme were compared to complement the findings from a diagnosis-based analysis.ResultsAmong 5493 patients with RA (BNT162b2: 653; CoronaVac: 671; non-vaccinated: 4169), propensity-scored weighted Poisson regression showed no significant association between arthritis flare and COVID-19 vaccination ((BNT162b2: adjusted incidence rate ratio 0.86, 95% Confidence Interval 0.73 to 1.01); CoronaVac: 0.87 (0.74 to 1.02)). The distribution of weekly rheumatic drug prescriptions showed no significant differences among the three groups since the launch of the mass vaccination programme (all p values >0.1 from Kruskal-Wallis test).ConclusionsCurrent evidence does not support that full vaccination of mRNA or inactivated virus COVID-19 vaccines is associated with possible arthritis flare.

Background Post‐marketing pharmacovigilance data are scant on the safety of Covid‐19 vaccines among people with previous SARS‐CoV‐2 infection compared with ordinary vaccine recipients. We compared the post‐vaccination adverse events of special interests (AESI), accident and emergency room (A&E) visit, and hospitalization between these two groups. Methods We conducted a retrospective cohort study using a territory‐wide public healthcare database with population‐based vaccination records in Hong Kong. Results In total, 3922 vaccine recipients with previous SARS‑CoV‑2 infection and 1,137,583 vaccine recipients without previous SARS‑CoV‑2 infection were included. No significant association was observed between previous SARS‑CoV‑2 infection and AESI or hospitalization. Previous SARS‑CoV‑2 infection was significantly associated with a lower risk of A&E visit (CoronaVac: hazard ratios [HR] = 0.56, 95% confidence intervals [CI]: 0.32–0.99; Comirnaty: HR = 0.62, 95% CI: 0.47–0.82). Conclusion No safety signal of Covid‐19 vaccination was detected from the comparison between vaccine recipients with previous SARS‐CoV‐2 infection and those without infection.

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Objective CoronaVac (Sinovac) Covid-19 vaccine has recently been approved for emergency use by the World Health Organization. However, data on its reactogenicity in real-world settings is scant. This study aimed to compare self-reported post-vaccination adverse reactions between CoronaVac and Comirnaty (Pfizer-BioNTech). Methods We adopted a prospective cohort study design using online surveys from the day of first-dose vaccination with intensive follow-up through two weeks after the second dose (11 time points). The primary outcome was adverse reactions (any versus none) and secondary outcomes were the sub-categories of adverse reactions (local, systemic, and severe allergic reactions). Potential effect modification across multimorbidity status, older age, and sex was examined. Results In total, 2,098 participants who were scheduled to complete the 14th-day survey were included, with 46.2% receiving Comirnaty. Retention rate two weeks after the second dose was 81.0% for the CoronaVac group and 83.6% for the Comirnaty group. Throughout the follow-up period, 801 (82.7%) of those receiving Comirnaty and 543 (48.1%) of those receiving CoronaVac reported adverse reactions. Adjusted analysis suggested that compared with Comirnaty, CoronaVac was associated with 83%-reduced odds of any adverse reactions [adjusted odds ratio (AOR) = 0.17, 95% confidence interval (CI) 0.15–0.20], 92%-reduced odds of local adverse reactions (AOR = 0.08, 95% CI 0.06–0.09), and 76%-reduced odds of systemic adverse reactions (AOR = 0.24, 95% CI 0.16–0.28). No significant effect modification was identified. Conclusion This post-marketing study comparing the reactogenicity of Covid-19 vaccines suggests a lower risk of self-reported adverse reactions following vaccination with CoronaVac compared with Comirnaty.