Incidence of sinus thrombosis with thrombocytopenia-A nation-wide register study.

Safe vaccination is essential for mitigation of the COVID-19 pandemic. Two adenoviral vector vaccines, ChAdOx1 nCov-19 (AstraZeneca) and Ad26.COV2.S (Johnson&Johnson/Janssen) have shown to be effective and they are distributed globally, but reports on serious cerebral venous sinus thrombosis (CVST) associated with thrombocytopenia, have emerged. Our objective was to evaluate the background incidence of CVST with thrombocytopenia and to compare it to incidences following COVID-19 vaccines. We conducted a register-based nation-wide cohort study in Finland, including all 5.5 million individuals alive in Finland, 1 Jan 2020. COVID-19 vaccinations registered in the National Vaccination Register served as the exposure. We detected CVST admissions or hospital visits recorded in the hospital discharge register from Jan 1, 2020 through April 2, 2021. We confirmed the diagnosis of CVST and thrombocytopenia (platelet count <150,000 per cubic millimeter) using radiology reports and laboratory data. By Poisson regression, we compared the baseline incidences to the risks within four weeks after COVID-19 vaccinations. Out of the 167 CVST episodes identified in the registers, 117 were confirmed as CVST, 18 of which coincided with thrombocytopenia (baseline incidence 0.18 per 28 days per million persons). We found 2 episodes of CVST with thrombocytopenia within 28 days of the first ChAdOx1 nCov-19 vaccination (among 200,397 vaccinated, aged 16 or above). No cases were found following the first mRNA vaccine dose among 782,604 vaccinated. The background incidence of CVST combined with thrombocytopenia was minuscule compared to the incidence during the weeks following the ChAdOx1 nCov-19 vaccination. Accurate estimation of the baseline incidence is essential in the critical appraisal of the benefit-risk of any vaccination program.

The association of adverse events with bivalent human papilloma virus vaccination: A nationwide register-based cohort study in Finland.

BACKGROUND: A bivalent HPV vaccine (Cervarix®; HPV2, GlaxoSmithKline) was introduced into the Finnish national vaccination programme (NVP) in November 2013 for girls aged 11-13 years with a catch-up for 14-15 year-olds. We evaluated the association between HPV2 and selected autoimmune diseases and clinical syndromes by conducting a nation-wide retrospective register-based cohort study. METHODS: First life-time occurrences of the relevant ICD-10 codes in girls aged 11-15 years between Nov-2013 and Dec-2016 were obtained from the national hospital discharge register. Population denominators were obtained from the Population Information System and vaccination records from the National Vaccination Register. Registers were linked using unique personal identity codes. Association between HPV2 and 38 selected outcomes were studied using Cox regression, with age as the main time-scale and the first vaccination dose as the time-dependent exposure. The hazard ratios (HR) with 95%CI were assessed according to the time since exposure (entire follow-up, 0-180/181-365/>365 days). RESULTS: Of 240 605 girls eligible for HPV2 vaccination, 134 615 (56%) were vaccinated. After adjustment for geographical area (6 hospital districts), country of origin (Finnish-born/not) and number of hospital contacts from 9 through 10 years of age, HRs ranged from 0.34 (95%CI 0.11-1.05) to 8.37 (95%CI 0.85-82.54) and HPV2 vaccination was not statistically significantly associated with a higher risk of any outcome during the entire follow-up. CONCLUSIONS: This study found no significantly increased risk for the selected outcomes after the HPV vaccination in girls 11-15 years of age. These results provide valid evidence to counterbalance public scepticism, fears of adverse events and possible opposition to HPV vaccination and consequently can contribute to increase HPV vaccination coverage in Finland as well as elsewhere.