Air travel during pregnancy and the risk of venous thrombosis.

BACKGROUND: Pregnancy and air travel independently increase the risk of venous thrombosis. However, there is a lack of data regarding the added risk, if at all, of thrombosis after air travel during pregnancy. OBJECTIVE: This study aimed to determine the potential added risk of venous thromboembolism among pregnant women who traveled by air. STUDY DESIGN: This was an observational retrospective study using data from 452,663 live births between the years 2010 to 2019. The study group consisted of women who flew during pregnancy. Data of pregnant women who flew during pregnancy were compared with that of pregnant women who did not fly during pregnancy. The primary outcome was venous thromboembolism during pregnancy and in the postpartum period. A case of venous thromboembolism was deemed related to air travel only if it occurred up to 8 weeks after the return flight (exposure time). Propensity score weighting Poisson regression was calculated to assess the effect and to control selection biases. Risk per day was calculated. RESULTS: Overall, 421,125 live births were included. Of those cases, 33,674 (8%) had traveled by air during pregnancy (study group), and 387,451 (92%) did not (control group). There were 6 cases of venous thromboembolism after a flight that occurred during the exposure time of 8 weeks and 285 cases of venous thromboembolism in the control group (0.05% vs 0.07%; P=.158). When the propensity weighting Poisson regression was calculated as risk per day, there was a significantly increased risk between the study and control groups (0.00031% vs 0.00022%; hazard ratio, 1.406; P=.005). CONCLUSION: The overall risk of venous thromboembolism after air travel is low; however, our study found that the risk of venous thromboembolism during pregnancy is increased by air traveling.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Naturally Acquired Immunity versus Vaccine-induced Immunity, Reinfections versus Breakthrough Infections: A Retrospective Cohort Study.

BACKGROUND: Waning of protection against infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) conferred by 2 doses of the BNT162b2 vaccine begins shortly after inoculation and becomes substantial within 4 months. With that, the impact of prior infection on incident SARS-CoV-2 reinfection is unclear. Therefore, we examined the long-term protection of naturally acquired immunity (protection conferred by previous infection) compared to vaccine-induced immunity. METHODS: A retrospective observational study of 124 500 persons, compared 2 groups: (1) SARS-CoV-2-naive individuals who received a 2-dose regimen of the BioNTech/Pfizer mRNA BNT162b2 vaccine, and (2) previously infected individuals who have not been vaccinated. Two multivariate logistic regression models were applied, evaluating four SARS-CoV-2-related outcomes-infection, symptomatic disease (coronavirus disease 2019 [COVID-19]), hospitalization, and death-between 1 June and 14 August 2021, when the Delta variant was dominant in Israel. RESULTS: SARS-CoV-2-naive vaccinees had a 13.06-fold (95% confidence interval [CI], 8.08-21.11) increased risk for breakthrough infection with the Delta variant compared to unvaccinated-previously-infected individuals, when the first event (infection or vaccination) occurred during January and February of 2021. The increased risk was significant for symptomatic disease as well. When allowing the infection to occur at any time between March 2020 and February 2021, evidence of waning naturally acquired immunity was demonstrated, although SARS-CoV-2 naive vaccinees still had a 5.96-fold (95% CI: 4.85-7.33) increased risk for breakthrough infection and a 7.13-fold (95% CI: 5.51-9.21) increased risk for symptomatic disease. CONCLUSIONS: Naturally acquired immunity confers stronger protection against infection and symptomatic disease caused by the Delta variant of SARS-CoV-2, compared to the BNT162b2 2-dose vaccine-indued immunity.

The Incidence of SARS-CoV-2 Reinfection in Persons With Naturally Acquired Immunity With and Without Subsequent Receipt of a Single Dose of BNT162b2 Vaccine : A Retrospective Cohort Study.

BACKGROUND: There is insufficient evidence regarding the magnitude and durability of protection conferred by a combined effect of naturally acquired immunity after SARS-CoV-2 infection and vaccine-induced immunity. OBJECTIVE: To compare the incidence rate of SARS-CoV-2 reinfection in previously infected persons to that of previously infected persons who subsequently received a single dose of BNT162b2 messenger RNA vaccine. DESIGN: A retrospective cohort study emulating a randomized controlled target trial through a series of nested trials. SETTING: Nationally centralized database of Maccabi Healthcare Services, Israel. PARTICIPANTS: Persons with documented SARS-CoV-2 infection who did not receive subsequent SARS-CoV-2 vaccination were compared with persons with documented SARS-CoV-2 infection who received a single dose of the BNT162b2 vaccine at least 3 months after infection. INTERVENTION: Forty-one randomized controlled trials were emulated, in which 107 413 Maccabi Healthcare Services' members aged 16 years and older were eligible for at least 1 trial. MEASUREMENTS: SARS-CoV-2-related outcomes of infection, symptomatic disease, hospitalization, and death, between 2 March and 13 December 2021. RESULTS: A statistically significant decreased risk (hazard ratio, 0.18 [95% CI, 0.15 to 0.20]) for reinfection was found among persons who were previously infected and then vaccinated versus those who were previously infected but remained unvaccinated. In addition, there was a decreased risk for symptomatic disease (hazard ratio, 0.24 [CI, 0.20 to 0.29]) among previously infected and vaccinated persons compared with those who were not vaccinated after infection. No COVID-19-related mortality cases were found. LIMITATION: Hybrid protection against non-Delta variants could not be inferred. CONCLUSION: Persons previously infected with SARS-CoV-2 gained additional protection against reinfection and COVID-19 from a subsequent single dose of the BNT162b2 vaccine. Nonetheless, even without a subsequent vaccination, reinfection appeared relatively rare. PRIMARY FUNDING SOURCE: None.