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Background: Pregnant individuals have been receiving COVID-19 vaccines following pre-authorisation clinical trials in non-pregnant people. This study aimed to determine the frequency and nature of significant health events among pregnant females after COVID-19 vaccination, compared with unvaccinated pregnant controls and vaccinated non-pregnant individuals., Methods: We did an observational cohort study, set in seven Canadian provinces and territories including Ontario, Quebec, British Columbia, Alberta, Nova Scotia, Yukon, and Prince Edward Island. Eligibility criteria for vaccinated individuals were a first dose of a COVID-19 vaccine within the previous 7 days; an active email address and telephone number; ability to communicate in English or French; and residence in the aforementioned provinces or territories. Study participants were pregnant and non-pregnant females aged 15-49 years. Individuals were able to participate as controls if they were unvaccinated and fulfilled the other criteria. Data were collected primarily by self-reported survey after both vaccine doses, with telephone follow-up for those reporting any medically attended event. Participants reported significant health events (new or worsening of a health event sufficient to cause work or school absenteeism, medical consultation, or prevent daily activities) occurring within 7 days of vaccination or within the past 7 days for unvaccinated individuals. We employed multivariable logistic regression to examine significant health events associated with mRNA vaccines, adjusting for age group, previous SARS-CoV-2 infection, and trimester, as appropriate., Findings: As of Nov 4, 2021, 191 360 women aged 15-49 years with known pregnancy status had completed the first vaccine dose survey and 94 937 had completed the second dose survey. 180 388 received one dose and 94 262 received a second dose of an mRNA vaccine, with 5597 pregnant participants receiving dose one and 3108 receiving dose two, and 174 765 non-pregnant participants receiving dose one and 91 131 receiving dose two. Of 6179 included unvaccinated control participants, 339 were pregnant and 5840 were not pregnant. Overall, 226 (4·0%) of 5597 vaccinated pregnant females reported a significant health event after dose one of an mRNA vaccine, and 227 (7·3%) of 3108 after dose two, compared with 11 (3·2%) of 339 pregnant unvaccinated females. Pregnant vaccinated females had an increased odds of a significant health event within 7 days of the vaccine after dose two of mRNA-1273 (adjusted odds ratio [aOR] 4·4 [95% CI 2·4-8·3]) compared with pregnant unvaccinated controls within the past 7 days, but not after dose one of mRNA-1273 or any dose of BNT162b2. Pregnant vaccinated females had decreased odds of a significant health event compared with non-pregnant vaccinated females after both dose one (aOR 0·63 [95% CI 0·55-0·72]) and dose two (aOR 0·62 [0·54-0·71]) of any mRNA vaccination. There were no significant differences in any analyses when restricted to events which led to medical attention., Interpretation: COVID-19 mRNA vaccines have a good safety profile in pregnancy. These data can be used to appropriately inform pregnant people regarding reactogenicity of COVID-19 vaccines during pregnancy, and should be considered alongside effectiveness and immunogenicity data to make appropriate recommendations about best use of COVID-19 vaccines in pregnancy., Funding: Canadian Institutes of Health Research, Public Health Agency of Canada., Competing Interests: Declaration of interests MS has been an investigator on projects funded by GlaxoSmithKline, Merck, Moderna, Pfizer, Sanofi-Pasteur, Seqirus, Symvivo, and VBI Vaccines. All funds have been paid to his institute, and he has not received any personal payments. OGV has been an investigator, coinvestigator, or expert panelist on projects funded by GlaxoSmithKline, Merck, Pfizer, and Seqirus, outside of the submitted work. JDK has been an investigator on projects funded by GlaxoSmithKline, Merck, Moderna, and Pfizer. All funds have been paid to his institute, and he has not received any personal payments. KAT has been an investigator on projects funded by GlaxoSmithKline. All funds have been paid to her institute, and she has not received any personal payments. JEI has been an investigator on projects funded by GlaxoSmithKline, and Sanofi-Pasteur. All funds have been paid to her institute, and she has not received any personal payments. AJM has been an investigator on projects funded by GlaxoSmithKline, Merck, Pfizer, Sanofi-Pasteur, and Seqirus, with funds paid to her institution, and has received honoraria for participation in advisory boards from Astra-Zeneca, GlaxoSmithKline, Medicago, Merck, Moderna, Pfizer, Sanofi-Pasteur, Seqirus, and for presentations from Astra-Zeneca, and Moderna. GDS has been an investigator on a project funded by Pfizer. All funds have been paid to his institute, and he has not received any personal payments. All other authors declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This prospective cohort study, performed during the 2009 influenza A(H1N1) pandemic, was aimed to determine whether adults working in acute care hospitals were at higher risk than other working adults for influenza and to assess risk factors for influenza among health care workers (HCWs). We assessed the risk for influenza among 563 HCWs and 169 non-HCWs using PCR to test nasal swab samples collected during acute respiratory illness; results for 13 (2.2%) HCWs and 7 (4.1%) non-HCWs were positive for influenza. Influenza infection was associated with contact with family members who had acute respiratory illnesses (adjusted odds ratio [AOR]: 6.9, 95% CI 2.2-21.8); performing aerosol-generating medical procedures (AOR 2.0, 95% CI 1.1-3.5); and low self-reported adherence to hand hygiene recommendations (AOR 0.9, 95% CI 0.7-1.0). Contact with persons with acute respiratory illness, rather than workplace, was associated with influenza infection. Adherence to infection control recommendations may prevent influenza among HCWs.

Background: Each year, a large number of Canadians travel to regions of the world where hepatitis A remains endemic. Many of these travelers are not immune and the current preventive strategy relies wholly on self-referral to a travel clinic. All of the costs associated with such a visit are assumed by the traveler. We estimated the effectiveness of this strategy., Methods: This case-control study included 108 travel-related hepatitis A cases with onset of disease between 1997 and 1999 and 620 controls who traveled during the same period., Results: Hepatitis A was strongly associated with high-risk travel (Odds Ratio = 7.2, 95% Confidence Interval 1.76-29.4), but only 7% of cases were found in this category. The risk of hepatitis A was 5 times lower in travelers who visited a travel clinic than in those who did not (80% efficacy). However, only 14% of the controls visited a travel clinic. As a result, the effectiveness of the current strategy is estimated to be 11% (80% of 14%)., Conclusions: Hepatitis A in travelers can be prevented effectively by attendance at a travel clinic. Unfortunately, most travelers do not visit such clinics prior to departure. Even if all high-risk travelers were to visit a travel clinic and receive vaccination, this would have negligible impact on the number of travel-related hepatitis A cases (approximately 7% reduction). The current strategy for the prevention of hepatitis A in travelers is ineffective and should be reexamined.

The protection provided by one or two doses of measles vaccine was compared, as was the effect of the timing of delivery of the doses on the protection provided. A total of 5542 measles cases occurred in Ontario, Canada, between January 1990 and December 1996. Three controls per case were matched for age and residence. Children who received a single dose at age 15 months and older were 5 times more likely to contract measles than were children who received two doses of vaccine after their first birthday. Among children given two doses of vaccines, the risk of measles was 3 times greater in those who had their first vaccination at age 11 months compared with children who first received vaccine after age 1 year, but the protection was independent of the interval between doses. Delaying the second dose >6 months after the first does not increase protection.