Safety of Pfizer-BioNtech COVID-19 Vaccine in Healthcare Workers, Singapore

Background. On 14 December 2020, the Pfizer-BioNTech coronavirus disease 2019 (COVID-19) vaccine was granted emergency use authorization in Singapore. Healthcare workers (HCW) were prioritized to receive the vaccine. We aim to investigate the side effects and risk factors for allergic reactions in our institution. Methods. All HCW vaccinations were recorded in an electronic centralized database. All reactions occurring within a 30-minute observation period post vaccination were recorded. Staff were required to report any vaccine-related medical consult including hospitalization occurring within 14 days after vaccination. Moderate/severe reactions were assessed by a medical team and determined if the reactions were probable allergic reactions with consultation with an Allergist. We extracted data from 8 Jan 2021 to 30 April 2021. Results. 5030 and 159 HCW completed 2 doses and 1 dose of the vaccine respectively. There were 1056 HCWs (20.3%) with self-reported pre-existing allergy. There were 114 (1.1%) reactions occurring without the 30-minute observation period, and 64 (56.1%) were related to first dose of vaccine. The most common side effect experienced was aches or pain on any part of the body (n=46, 40.4%) followed by fatigue and/or giddiness (n=45, 39.5%), palpitations and/or shortness of breath (n=22, 19.3%), systemic rash and/or angioedema (n=12, 10.5%) and nausea and/or vomiting (n=12, 10.5%). A total of 23 HCWs complained of systemic rash and/or angioedema that occurred anytime post vaccination. Fifteen HCWs (0.29% of the cohort) were considered to have probable allergic reaction to the vaccine. None of the reactions were classified as anaphylaxis or severe reactions, but 4 HCWs required short hospitalization stay for observation. HCWs with pre-existing allergy had 2.6 times the risk of having probable vaccine-related allergic reaction than HCWs without pre-existing allergy (RR 2.6, 95% CI 0.9 to 7.3, p=0.068) but this was not statistically significant. Conclusion. No anaphylaxis or severe reactions were observed in our institution. Acute side effects in our cohort were in line with published trial reports. We noted a raised relative risk of 2.6 of pre-existing allergy with probable vaccine-related allergic reaction but this was not statistically significant.

SARS-CoV-2 viral RNA load dynamics in the nasopharynx of infected children.

It is important to understand the temporal trend of the paediatric severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral load to estimate the transmission potential of children in schools and communities. We determined the differences in SARS-CoV-2 viral load dynamics between nasopharyngeal samples of infected asymptomatic and symptomatic children. Serial cycle threshold values of SARS-CoV-2 from the nasopharynx of a cohort of infected children were collected for analysis. Among 17 infected children, 10 (58.8%) were symptomatic. Symptomatic children, when compared to asymptomatic children, had higher viral loads (mean cycle threshold on day 7 of illness 28.6 vs. 36.7, P = 0.02). Peak SARS-CoV-2 viral loads occurred around day 2 of illness in infected children. Although we were unable to directly demonstrate infectivity, the detection of significant amount of virus in the upper airway of asymptomatic children suggest that they have the potential to shed and transmit SARS-CoV-2. Our study highlights the importance of contact tracing and screening for SARS-CoV-2 in children with epidemiological risk factors regardless of their symptom status, in order to improve containment of the virus in the community, including educational settings.

Time to Rt < 1 for COVID-19 public health lockdown measures.

The epidemiological target of lockdowns is to drive down the effective reproduction number (Rt) to less than 1. A key unknown is the duration that lockdowns need to be in place to achieve this and which lockdown measures are effective. Daily number of laboratory confirmed community coronavirus 2019 cases were extracted from regular reports from the Ministry of Health Singapore from 20 March 2020 to 4 May 2020. We generated daily Rt to estimate the time needed for these public health lockdown measures to control the spread of severe acute respiratory syndrome coronavirus 2 as demonstrated by Rt < 1. It took about 14 days of nationwide lockdown for the Rt trend to change and start falling. The upper limit of the 95% confidence interval for time to Rt < 1 was day 15 of lockdown. We have shown that it is possible to start 'bending the Rt curve' about 2 weeks after implementation of specific lockdown measures with strict compliance.