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Evidence Check - Epidemiology and transmission

Community transmission and hospital infection, stages of pandemic, immunity, vaccination.

AstraZeneca vaccine and blood clots

Added: 17 Mar 2021

Emerging evidence on AstraZeneca vaccine and blood clots
  • The BMJ (11 March 2021): Denmark temporarily suspended use of the AstraZeneca vaccine after reports of blood clots and one death. Eight other countries including Norway, Iceland, Austria, and Italy have also suspended use of the vaccine. Since this publication, at least 15 other countries have suspended AstraZeneca vaccinations. The reported cases include one with multiple thrombosis, who died 10 days after vaccination. Another case was admitted to hospital with pulmonary embolism after being vaccinated. There were two other reports of thromboembolic event cases received by the EMA.
  • European Medicines Agency (EMA) (11 March 2021): The EMA states there is currently no indication that vaccination has caused thromboembolic events. The safety committee states the vaccine’s benefits continue to outweigh its risks, and the vaccine can continue to be administered while investigation of cases of thromboembolic events is ongoing.
  • Therapeutic Goods Administration (12 March 2021): The TGA has received no reports of blood clots following use of the AstraZeneca vaccine in Australia. Extensive international experience does not indicate an increased risk of blood clots associated with the vaccine.
  • AstraZeneca (14 March 2021): A review of all available safety data of more than 17 million people vaccinated in the European Union and UK with the AstraZeneca vaccine has shown no evidence of an increased risk of pulmonary embolism, deep vein thrombosis or thrombocytopenia
  • in any defined age group, gender, batch
  • or in any particular country.
  • European Medicines Agency (15 March 2021): The overall number of thromboembolic events in vaccinated people does not seem to be higher than in the general population. While its investigation is ongoing, the EMA retains the view that the benefits of the AstraZeneca vaccine in preventing COVID-19, outweigh the risks of side effects.
  • UK Government (16 March): It has not been confirmed that the reports of blood clots were caused by the AstraZeneca COVID-19 vaccine. People should continue to get vaccinated.
  • CNCB News (16 March): Many countries, including the UK, Canada and Australia are continuing to deploy the vaccine and seeking to reassure citizens about its benefits.

Endemicity of SARS-CoV-2

Added: 17 Mar 2021

What evidence is available about the likelihood that SARS-CoV-2 will become endemic?
  • Endemicity refers to the extent to which a disease or infectious agent is always present within a given geographic area or population group.
  • Pre-COVID-19, four endemic coronaviruses (229E, NL63, OC43, and HKU1) were responsible for a large proportion of upper and lower respiratory tract infections.
  • Whether SARS-CoV-2, will also become endemic will be determined by the interplay between virus biology and immunity of the host population (see figure 1).
  • A weak adaptive immune response, waning immunity and viral immune escape can result in reinfection or infection in vaccinated populations. This leads to endemicity.(1)
  • A January 2021 survey of about 100 immunologists, infectious-disease researchers and virologists showed 90% thought SARS-CoV-2 will become endemic.(2)
  • Endemicity can take multiple forms. Several post-pandemic scenarios have been described.
  • Yearly outbreaks of SARS-CoV-2, if the duration of immunity proves to be similar to that of the other beta-coronaviruses (∼40 weeks).(1)
  • SARS-CoV-2 continues to circulate but becomes no more virulent than the common cold, with primary exposure in childhood.(3)
  • Apparent elimination of the virus followed by resurgence after a few years, if there is a longer immunity profile, coupled with a small degree of protective cross-immunity from other betacoronaviruses.(1, 4)
  • The nature of SARS-CoV-2 endemicity that emerges will require tailored and nuanced public health and policy responses in different jurisdictions.

AstraZeneca vaccine rollout

Added: 11 Mar 2021

What evidence is emerging regarding the effectiveness of the AstraZeneca vaccine, particularly regarding hospitalisations in the United Kingdom (UK)?
  • The AstraZeneca vaccine (AZD1222 / ChAdOx1) is a viral vector vaccine that can be stored at 2-8°C.
  • The original recommended schedule was two doses, 28 days apart.
  • The UK announced on 30 December 2020 its plan to administer two doses, 12 weeks apart.
  • In Australia, the Therapeutic Goods Administration has determined that the vaccine can be safely administered 4-12 weeks apart.
  • The AstraZeneca vaccine has an acceptable safety profile. Some European countries initially advised against use in older people due to lack of data. However, this is being reviewed and Germany has since approved the vaccine for those 65 years and over
  • BMJ (19 Feb 2021): The number of deaths in the UK within 28 days of a positive COVID-19 test reported as steadily falling. In the three weeks to 14 February 2021, deaths in care homes fell by 62% to a level previously seen around the end of October 2020. Hospital admissions fell in all age groups, however this may be as a result of the concurrent lockdown.
  • University of Edinburgh preprint (21 Feb 2021): Article showed that four weeks after the first doses of the Pfizer and AstraZeneca vaccines were administered in Scotland, the risk of hospitalisation from COVID-19 fell by up to 85% (95% confidence interval 76 to 91) and 94% (95% confidence interval 73 to 99), respectively
  • Lancet preprint (3 March 2021): Substantial reductions in the risk of COVID-19-related hospitalisation in elderly, frail patients with extensive co-morbid disease following a single dose of either Pfizer (71.4% reduction) or AstraZeneca (80.4% reduction) vaccines.
  • medRxiv preprint (4 March 2021): Single dose reported to be approximately 80% effective at preventing hospitalisation among people aged ≥70 years in UK. Significant reduction in symptomatic cases in older adults, with even greater protection against severe disease following a single dose of either Pfizer or AstraZeneca. Protection was maintained for the duration of follow-up (>6 weeks). Reports a clear effect of the vaccines against the UK variant of concern.

Emerging evidence about COVID-19 vaccines

Added: 25 Jan 2021
Updated: 5 Feb 2021

What evidence is emerging about the efficacy, safety and rollout of COVID-19 vaccines?
  • There are four main vaccine types: whole virus, protein subunit, nucleic acid and viral vector
  • To date, nine vaccines have been registered in one or more countries
  • Results of phase 3 trials have been published for two messenger RNA (mRNA) vaccines (Pfizer/BioNTech and Moderna) and one vector vaccine (Oxford/Astra-Zeneca).
  • There are different potential clinical endpoints for evaluating the efficacy of COVID-19 vaccines. These include SARS-CoV-2 infection, asymptomatic infection, COVID-19 (symptomatic disease), severe COVID-19, mortality and transmission.
  • In the published phase 3 studies to date, efficacy is reported using symptomatic disease as the primary endpoint.
  • Vaccine efficacy (using symptomatic disease as the primary endpoint) was 95.0% for the Pfizer/BioNTech vaccine, 94.1% for the Moderna vaccine and 70.4% for the Oxford/Astra-Zeneca vaccine (varying from 62.1% to 90.0% based on the schedule used).
  • All three vaccines had an acceptable safety profile.
  • It is not yet clear what vaccine efficacies and coverage levels will achieve herd immunity.
  • According to the World Health Organization, the vaccines that have been approved to date should provide protection against emerging SARS-CoV-2 variants, as they elicit a broad immune response. Evidence is however emerging that there may be some immune escape
  • The evidence on efficacy and effectiveness of COVID-19 vaccines is rapidly emerging. To date, there is limited to no information on efficacy re SARS-CoV-2 infection or asymptomatic infection, mortality and transmission. Nor is there published evidence on the impact of changes to dosage schedules, the duration of protection, different vaccination strategies or mixed vaccine use.

SARS-CoV-2 variants

Added: 20 Jan 2021
Updated: 5 Feb 2021

What is the evidence of the new SARS-CoV-2 variants (20B/501Y.V1 and 20C/501Y.V2) in terms of their infectivity, virulence, and effectiveness of the current vaccines?
  • Viruses constantly change through mutation and over time new variants of a virus are expected to occur.
  • New SARS-CoV-2 variants have recently emerged, most notably in the United Kingdom (UK), known as 20B/501Y.V1, variant of concern (VOC) 202012/01, or B.1.1.7 lineage and in South Africa known as 20C/501Y.V2 or B.1.351 lineage.
  • Other variants have recently emerged in Nigeria and Japan.
  • According to the World Health Organization the vaccines that have been approved should provide protection against variants, as the vaccines elicit a broad immune response.
  • While public health measures such as physical distancing, limitations on large gatherings and masks should remain effective, control of a more transmissible variant will require more widespread adoption of these measures.

Deployment and vaccination plan for COVID-19

Added: 9 Dec 2020

What is the current guidance on developing a vaccination plan for COVID-19?
  • The World Health Organization (WHO) has released an interim guidance on developing a national deployment and vaccination plan for COVID-19 vaccines. This evidence brief provides a summary of this document, with supplementary information specific to the Australian context.
  • As of 2 December 2020, on the National Centre for Immunisation Research and Surveillance website, there were 213 vaccine candidates including 45 vaccine candidates in human clinical trials and 11 vaccine candidates in phase III clinical trials.
  • It is anticipated that most SARS-CoV-2 vaccines will require at least two doses for optimal immunogenicity. Storage and distribution temperature will likely be +2°C to +8°C for most vaccines but may require an ultra-cold chain of -20°C to -80°C storage for certain products.
  • The COVID-19 vaccine products are likely to have varying vaccine characteristics and presentations and will require different administration techniques.
  • The Australian government has established vaccination policy and secured agreements for the supply of four promising COVID-19 vaccines, provided they prove to be safe and effective.
  • Early studies looking at hypothetical COVID-19 vaccine acceptance amongst Australians estimated that approximately 4.9% would refuse and 9.4% are indifferent about receiving a COVID-19 vaccine. Inadequate health literacy and lower education level were associated with vaccine reluctance.

High-risk settings for transmission of COVID-19 evidence check

Added: 18 Nov 2020

What is the evidence for transmission of COVID-19 in different settings, and which settings are high-risk?
  • A statement from the Australian Health Protection Principal Committee (AHPPC) describes several very high-risk environments including nightclubs, dance venues, and large unstructured outdoor events such as music festivals, food festivals, school guardians’ festivals, carnivals, community sporting events and other non-ticketed spectator events. These events are high risk due to factors such as but not limited to large numbers, close proximity and mixing between groups of people.
  • Healthcare and residential aged care settings are known to be high risk but are excluded from this review
  • A systematic review identified 22 types of settings, predominantly indoor settings that result in SARS-CoV-2 transmission clusters. Risk was classified based on the number of infections per cluster or the proportion of people in that setting who became infected. Most clusters involved fewer than 100 cases, with the exceptions being in large religious gatherings, food processing plants, schools, shopping, and large co-habiting settings (worker dormitories, prisons and ships). Other settings with examples of clusters between 50–100 cases in size were weddings, sporting events, bars, shops and workplaces.
  • A rapid review, prepared by The National Collaboration Centre for Methods and Tools looking at risk of COVID-19 transmission across different indoor settings in the community, reported that households and shared accommodations (e.g. cruise ships) thus far appear to be the most prevalent locations for infection clusters. In settings involving indoor physical activity (gyms and fitness classes), attack rates are highly variable and range from 7.3-26.3%. Transmission appeared to occur more commonly from fitness instructors to participants. Furthermore, modelling studies estimated risk level for different indoor scenarios found ventilation, reducing crowd size, wearing a mask and physical distancing may decrease transmission risk.
  • Most evidence were from single case reports. For many settings, there were insufficient data to determine whether the settings are categorically high risk. Studies were mostly descriptive, with some concluding that transmission was likely facilitated by close proximity. Indoor settings featured in the literature included: Establishments providing accommodation: homeless shelters, prisons, work dormitories, cruise ships Occupational settings: military, factories, offices, call centres and schools. Social/recreational settings: family and religious gatherings, shopping centres, choir, restaurants, fitness centres and aircrafts.

Infection control recommendations in the emergency department according to local transmission risk evidence check

Added: 4 Nov 2020

What personal protective equipment (PPE) and other infection control measures are implemented in the emergency department (ED) during COVID-19
and do they differ according to levels of community transmission?
  • Studies of ED infection control measures in response to COVID-19 are predominantly descriptive in nature, and generally do not provide detail regarding levels of local disease prevalence. Risk assessment in the ED generally considers the risk an individual patient has of contracting COVID-19 based on their history and clinical picture, rather than adopting a population perspective, which considers local transmission rates. Frequently reported infection control or risk mitigation measures used in EDs include the following.
  • Recommendations for PPE use – PPE recommendations are mainly based on patient risk stratification or assessments of aerosol generating procedures. Studies describe the use of full PPE when interacting with patients with symptoms or high risk epidemiological history, when working in designated ‘fever clinics’ or triage, or when performing aerosol generating procedures.(1-6). One study from Europe found that 82% of EDs surveyed implemented surgical mask use for patients.(4)
  • Triage – dedicated triage stations either in tents or prefab houses located outside the main ED building, at the entrance or inside the ED in a separate area.(1, 5, 7-19)
  • Zoning or partitioning of the ED areas – division of triage, waiting and clinical areas in the ED into separated zones for placing patients based on their COVID-19 risk stratification.(2, 3, 8-13, 18, 20-25) Some recommend differential PPE and the use of protocols for healthcare providers working in different zones.(2, 7, 24)
  • Negative pressure rooms – use of fans in existing structures, or medical tents are described.(4, 8, 10, 11, 26)
  • Telemedicine – audio and video devices or call centres to provide assessment or consultation for patients either before they present to ED, or while being triaged or waiting or isolating in the ED rooms, especially for those not in immediate need for physical examination or resuscitation.(7, 8, 18, 19, 22, 27-30)
  • Healthcare worker cross-infection prevention – a range of interventions are described including: reducing the number of non-clinical employees in the ED
  • using telemedicine, separating dining, rest and office areas and partitioning spaces using transparent boards
  • using portable computers, using instant messaging for disseminating information
  • regular monitoring and logging of healthcare provider symptoms and enhanced cleaning of work areas and equipment.(3, 5, 12, 28, 31, 32)
  • Portable or mobile diagnostic testing equipment – use of portable X-ray in different zones of ED or a truck equipped with diagnostic devices.(11, 33)

Daily Evidence Digest

Rapid evidence checks are based on a simplified review method and may not be entirely exhaustive, but aim to provide a balanced assessment of what is already known about a specific problem or issue. This brief has not been peer-reviewed and should not be a substitute for individual clinical judgement, nor is it an endorsed position of NSW Health.

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