COVID-19 evidence: a Cochrane round-up

Sarah Chapman highlights Cochrane evidence on COVID-19 and other health effects of the pandemic, with links to reviews, blogs and other Cochrane resources. 

While we’ve all been adapting to huge and sudden changes in our lives and healthcare workers have been meeting unprecedented challenges, scientists have scrambled to produce research evidence relevant to the pandemic. Cochrane is responding by producing rapid reviews of this new evidence on priority topics, and these are updated as new evidence emerges. They show that much of the research that has been done so far leaves us with more unanswered questions than answers, but we must hope that this changes as new studies are available to add to the reviews.

Here’s a round-up of some of the Cochrane evidence so far. On this page, there are sections on:

Detecting COVID-19

Signs and symptoms of COVID-19

We’re hearing a lot about temperature checks, which in many places are being used determine whether someone may enter a care home, hairdressers or other building. But what’s the evidence? We’ve blogged about a Cochrane Review, published in July 2020, on the accuracy of any signs and symptoms, either alone or in combination, for diagnosing COVID‐19.

Take-home points: A Cochrane Review has looked at the available evidence on the accuracy of clinical signs and symptoms for diagnosing COVID-19. Based on the currently available evidence, neither absence nor presence of signs or symptoms are accurate enough to rule in or rule out disease. There is a need for evidence on combinations of signs and symptoms and in different settings (particularly GP practices) and age groups (children, older adults). This living systematic review will be updated as often as is feasible to take account of new evidence as it emerges. 

You can read the blog: “Signs and symptoms of COVID-19: new Cochrane evidence“. There is also a podcast and a Cochrane Clinical Answer.

Antibody tests for COVID-19

Antibody tests have the potential to identify people who have had COVID-19. A Cochrane Review ‘Antibody tests for identification of current and past infection with SARS-CoV-2′ was published in June 2020 and we have blogged about it: “Antibody tests for COVID-19: new evidence on test accuracy and some considerations“.

Take-home pointsAntibody tests have the potential to identify people who have had COVID-19.A Cochrane Rapid Review shows that antibody tests could have a useful role in detecting if someone has had COVID-19. As with any diagnostic test, there will be a number of people falsely diagnosed as having COVID-19, and a number of people who do have the disease will be missed; timing makes a big difference to the accuracy of the test.Test accuracy is only one consideration in decisions about the purposes and implications of widespread testing for COVID-19 antibodies.

Rapid tests for COVID-19, done during a health care visit

Tests to detect COVID-19 that can give a result ‘while you wait’ (within a couple of hours) could be really useful, helping people isolate quickly to reduce the spread of infection.  A Cochrane Review on Rapid, point‐of‐care antigen and molecular‐based tests for diagnosis of SARS‐CoV‐2 infection was published in August 2020. The review authors anticipate that they will have an update of the review this autumn and lead author Jacqueline Dinnes is going to blog about the updated review here.

Routine laboratory tests – how good are they for detecting COVID-19?

Routine blood tests, processed in laboratories, include counts of different types of white blood cells that help fight infection and identifying proteins (‘markers’) that can indicate general inflammation and organ damage. These are widely available and in some places might be the only tests available for diagnosing COVID-19.

A Cochrane Review Routine laboratory testing to determine if a patient has COVID‐19 (November 2020) has looked for evidence on the accuracy of these tests in people with suspected COVID-19 for diagnosing the disease and for prioritizing people for different levels of treatment. The review includes 21 studies looking at 67 routine laboratory tests for COVID-19, all in people who were patients in hospitals.

The bottom line: “Although these tests give an indication about the general health status of patients and some tests may be specific indicators for inflammatory processes, none of the tests we investigated are useful for accurately ruling in or ruling out COVID‐19 on their own.”

Screening for COVID-19

Screening people who have mild or no symptoms but have COVID-19, to find out if someone’s infected, is another strategy that has potential to help reduce the spread of infection, as those who are found to have the virus could then isolate, for example. A Cochrane rapid review on universal screening for SARS‐CoV‐2 infection was published in September 2020. The evidence base is currently very limited and highlights uncertainty about the effectiveness of screening for COVID-19. The review finds that:

“One‐time screening in apparently healthy people is likely to miss people who are infected. We are unsure whether combined screenings, repeated symptom assessment, or rapid laboratory tests are useful.

As more people become infected, screening will identify more cases. However, because screening can miss people who are infected, public health measures such as face coverings, physical distancing, and quarantine for those who are apparently healthy, continue to be very important.”

Here is a video summary.

Thoracic (chest) imaging tests for COVID-19

A Cochrane Review on thoracic imaging tests for the diagnosis of COVID-19 was published in September 2020 and updated for the first time in November 2020. It brings together evidence on the diagnostic accuracy of chest (thoracic) imaging (computed tomography (CT), X‐ray and ultrasound) in people with suspected COVID‐19. This is one of a suite of Cochrane ‘living systematic reviews’ summarising evidence on the accuracy of different imaging tests and diagnostic features in people regardless of their symptoms, grouped according to the research questions and settings.

The review includes 34 studies, involving people with suspected COVID-19, of whom just over half had a final diagnosis of COVID-19. Most of the studies looked at chest CT. The evidence so far suggests that chest CT is better at ruling out COVID-19 infection than distinguishing it from other respiratory problems. However, the authors’ confidence in the evidence is limited by poor study quality, and the fact that about a quarter of the studies were published as pre-prints – not subject to the same rigorous checks as other published studies.

The review authors note that since the first version of the review the accuracy of chest CT has improved, perhaps because of better definitions of a positive COVID-19 diagnosis and because of knowledge and skills increasing as the pandemic goes on.

Measures to control the spread of COVID-19

School-based measures to contain the COVID-19 pandemic

Shutting schools was one of the earliest responses to the pandemic in many countries. As well as potential benefits of this strategy for limiting the spread of infection there are many potential harms, including worsening health and wellbeing for children and widening inequalities. Alternatives to school closure are also being adopted, including the wearing of face masks, hand hygiene, changes to school activities, improved ventilation systems and screening. It will be important to have evidence of the effectiveness of these different measures to inform policy and practice.

Cochrane has published a scoping review on measures implemented in the school setting to contain the COVID‐19 pandemic (December 2020), to map the existing evidence. The review authors found 42 studies, of which 31 were mathematical modelling studies, evaluating a wide range of measures. This will form the basis of a review of the effectiveness of these measures.

Quarantine for controlling COVID-19

A Cochrane rapid review on quarantine alone or in combination with other public health measures to control COVID-19 was published in April 2020 and updated in September 2020. It is the focus of this blog: “Quarantine for controlling COVID-19 (coronavirus). New Cochrane evidence.”

A Cochrane Rapid Review, updated in September 2020, has found that COVID-19 mathematical modelling studies consistently report a benefit of quarantine in reducing the number of people who get infected with COVID-19 and who die from it. The number of studies has increased significantly in a short space of time since this review was first published in April 2020, but the evidence base is still limited. This is because most studies on COVID-19 are mathematical modelling studies that make different, important assumptions (for example, about how quickly the virus would spread). This Rapid Review was done in a short space of time as part of Cochrane’s organizational effort to meet the need for up-to-date summaries of evidence to support decision-making in combating the effects and impact of COVID-19. More Rapid Reviews, answering other important questions about COVID-19, are underway.

Watch a video of the lead author summarising the review’s findings. You might also be interested in this blog ““Stay at home” rules: what makes people more likely to stick to quarantine?“, which looks at two non-Cochrane rapid reviews from researchers at King’s College London.

Contact tracing

Contact tracing aims to reduce transmission of infection by identifying people who have been in contact with someone who has it, so that they can isolate. A Cochrane rapid review published in August 2020 looked at evidence on digital contact tracing technologies in epidemics.

The review highlights an evidence gap, the authors concluding that “the effectiveness of digital solutions is largely unproven as there are very few published data in real‐world outbreak settings.”

Personal Protective Equipment (PPE) for healthcare workers

Two Cochrane reviews contribute to the evidence base on PPE for healthcare workers and we have a blog about these: “Personal protective equipment (PPE) for healthcare workers: new Cochrane evidence“. They look at Personal protective equipment for preventing highly infectious diseases due to exposure to contaminated body fluids in healthcare staff (May 2020) and Barriers and facilitators to healthcare workers’ adherence with infection prevention and control (IPC) guidelines for respiratory infectious diseases: a rapid qualitative evidence synthesis (April 2020).

Take-home points • An updated review and a new rapid review on PPE have been produced as part of Cochrane’s organizational effort to meet the need for up-to-date summaries of evidence to support decision-making in combating the effects and impact of COVID-19. • These reviews contribute to the evidence base about a range of considerations in PPE use, including barriers and facilitators to healthcare workers adherence to infection prevention and control guidelines. There are some new, creative solutions being developed to address some of the issues associated with wearing PPE.

For the review on PPE there is a Cochrane Clinical Answer. For the review on barriers and facilitators there is podcast and a Cochrane Clinical Answer. Evidence Synthesis Ireland and Cochrane Ireland have also created an infographic summarising key messages.

Antimicrobial mouthrinses and nasal sprays to protect healthcare workers and patients at risk of COVID-19

Antimicrobial mouthrinses and nasal sprays have the potential to help people with COVID-19 fight infection and prevent them infecting healthcare workers who care for them. They might also offer some protection to healthcare workers, especially if they use them before doing aerosol-generating procedures, such as drilling teeth.

Three new Cochrane Reviews were published in September 2020 looking at different aspects of this. There is a helpful summary of all three in this Cochrane Oral Health Editorial base blog Antimicrobial mouthrinses and nasal sprays to protect healthcare workers and patients at risk of COVID-19, which also has links to each of the reviews. No completed studies were found for any of the reviews, so this is currently an evidence gap, but there are ongoing studies for two of these three reviews and all will be updated.

A Cochrane rapid review, published in September 2020, has looked at travel-related control measures to contain the COVID-19 pandemic. Not surprisingly, it highlights uncertainty about their effectiveness and a lack of reliable and ‘real-life’ evidence, but the authors will update the review soon and hope there may be better evidence to include. You can read about the review in this blog “Travel-related measures for controlling the spread of COVID-19: New Cochrane evidence“.

Take-home points A Cochrane rapid review has looked for evidence on the effectiveness of travel-related measures for controlling the spread of COVID-19. There is currently a lack of reliable evidence; much of the evidence comes from modelling studies. The effectiveness of travel-related measures is likely to be influenced by factors such as the stage of the pandemic and the implementation of other measures.

Treating people with COVID-19

Convalescent plasma – a possible treatment for COVID-19?

Many clinical trials are being done to investigate the potential benefits or harms of using plasma from people who have recovered from COVID-19 to treat people who are currently ill with it. This blog: “Convalescent plasma to treat people with COVID-19: the evidence so far” looks at a Cochrane rapid review on convalescent plasma to treat people with COVID-19, updated for the second time in October 2020 and highlights continued uncertainty about the potential effectiveness and safety of this treatment.

we are unable to assess the relative safety of convalescent plasma therapy. Take-home points: A Cochrane rapid review with 19 studies, including two small randomized controlled trials, shows that the effectiveness and safety of convalescent plasma for people with COVID-19 are uncertain. The review authors identified 138 ongoing studies, including 73 randomized trials. This review is being regularly updated as a ‘living systematic review’, based on monthly searches for new evidence, and the results are likely to change.  Chapman S. “Convalescent plasma to treat people with COVID-19: the evidence so far”. Evidently Cochrane blog, 15 May 2020, last updated 12 October 2020.

Oxygen therapy for adults in intensive care with acute respiratory distress syndrome

A Cochrane rapid review on oxygen targets in the intensive care unit during mechanical ventilation for acute respiratory distress syndrome has brought together evidence on this topic. The review authors explain the context:

“Acute respiratory distress syndrome (ARDS) is a very severe breathing problem with a high mortality rate (chance of dying). It has many potential causes, including viral infections such as COVID‐19, and there are no specific treatments for it except for giving patients oxygen via a ventilator (artificial breathing machine) on an intensive care unit, often for long periods of time. However, large amounts of oxygen (either a high concentration of oxygen or oxygen administered for a long period of time) are associated with increased harm due to other illnesses (e.g. heart attack or stroke).”

Here’s what they found:

Patients with acute respiratory distress syndrome (ARDS) and receiving oxygen through a breathing tube in intensive care may be more likely to survive beyond 90 days if they receive higher volumes of oxygen, compared with lower volumes. Whether patients receive a higher or lower volume of oxygen may make little or no difference to the number of days ventilated; the need for inotropic support (to stabilise circulation and optimise oxygen supply); or the likelihood of needing renal replacement therapy. However the evidence is very uncertain (all very low-certainty evidence). Effects on quality of life were not reported.The evidence is very uncertain about the potential harms of higher versus lower oxygen targets (very low-certainty evidence). Cochrane Review (published September 2020); one study with 205 mechanically ventilated patients in an intensive care setting, comparing conservative oxygen therapy with liberal oxygen therapy for seven days.

Prophylactic anticoagulants for people hospitalised with COVID-19

COVID‐19 may predispose people to getting blood clots in the arteries, veins and lungs. Venous and arterial thromboembolic complications affect 16% of people hospitalised with COVID‐19 and 31% to 49% of people with COVID‐19 in intensive care units, with 90% of such cases being venous thromboembolism. A Cochrane Review, Prophylactic anticoagulants for people hospitalised with COVID‐19, has looked for evidence on the effects of using blood thinning drugs to prevent this in people hospitalised with COVID-19.

As yet, there are no published randomised trials and the authors conclude that there is insufficient evidence to determine the risks and benefits of prophylactic anticoagulants in this population. However, they found 22 studies in progress which plan to evaluate 15,000 people, which will be considered for future updates of the review.

Care bundles for people with COVID-19 or related conditions in intensive care

Cochrane has published a scoping review on care bundles for improving outcomes in patients with COVID-19 or related conditions in intensive care (December 2020) to map the existing evidence. The review authors found 21 studies and also identified three ongoing studies. Seven included patients with COVID-19. Most care bundles involved practices related to breathing support or ventilator settings, or the positioning of a patient, and COVID‐19‐specific studies also focused on infection control and use of personal protective equipment (PPE). There now needs to be a systematic review of this evidence.

The impact of the pandemic on other areas of health and wellbeing

Resilience and mental health of frontline healthcare professionals

Working on the ‘front line’ as a health or social care professional during a pandemic is stressful and can negatively impact workers’ mental health. A Cochrane Review on interventions to support the resilience and mental health of frontline health and social care professionals during and after a disease outbreak, epidemic or pandemic aimed to assess the effects of such interventions and explore things that make it easier or harder to implement them, through both qualitative and qualitative evidence.

Intervention effects remain uncertain. They were explored in just one study. All 16 studies in the review had some limited evidence on things that might help interventions to be successfully delivered. This review highlights a need for robust evaluation of interventions and the review authors suggest that the current pandemic provides unique opportunities for doing so.

Interventions for heavy menstrual bleeding

Pandemics disrupt healthcare provision. With this in mind, a Cochrane overview of reviews (July 2020) has been done on interventions commonly available during pandemics for heavy menstrual bleeding. You can see summaries of the review here, including an infographic to help women make choices about treatment. There is also a podcast about this review and two Cochrane Clinical Answers. 

Routine vaccinations during the pandemic

The World Health Organization (WHO) has emphasized the importance of keeping up with routine vaccinations during the pandemic, advice endorsed by Public Health England. A Cochrane Review on vaccines for measles, mumps, rubella and varicella  in children (published April 2020) was discussed in this blog: “MMR vaccines: do they work and are they safe?“.

Take home points A Cochrane Review has shown that MMR vaccines are effective at preventing measles, mumps, rubella in children.The review found no evidence of an increased risk of autism from MMR vaccination.World Health Organization guidance, supported by Public Health England, advises having routine vaccinations during the COVID 19 pandemic.It is never too late to catch-up on MMR vaccination.

There are two Cochrane Clinical Answers related to this review.

Social isolation and loneliness in older people

With restrictions imposed during the pandemic increasing isolation for many, a Cochrane rapid review (May 2020) looked for evidence on video calls for reducing social isolation and loneliness in older people. We discuss the review in this blog: “Loneliness in older people: could video calls help?

Video calls have the potential to help older people stay connected with others and to reduce loneliness and social isolation. A Cochrane rapid review has highlighted that the evidence on the effects of video calls on loneliness, depression, quality of life and social isolation are very uncertain. It is important to consider an older person’s circumstances as well as their personal preferences for technology such as video calls.

There is also a podcast and a Cochrane Clinical Answer.

Quitting smoking to improve respiratory health

Given the current threat from COVID-19, an acute respiratory infection, there has never been a better time to stop smoking, and the World Health Organization is urging people to do so. We have looked at evidence from a new Cochrane Special Collection, COVID-19: Effective options for quitting smoking during the pandemic, in this blog: “Smoking and coronavirus (COVID-19): time to quit.”

Smoking increases the risk of getting acute respiratory infections and of being more severely affected, as does exposure to second-hand smoke. The Cochrane Special Collection, COVID-19: Effective options for quitting smoking during the pandemic, pulls together evidence including Cochrane Reviews on nicotine replacement, behavioural support such as telephone, internet and text messaging programmes, and gradual quitting. The Cochrane Reviews in the Special Collection focus on interventions that are feasible under public health measures that restrict face to face contact with health practitioners.

Coronavirus (COVID-19): Special Collections

The Special Collection on quitting smoking during the pandemic is one of seven Cochrane Special Collections on COVID-19. Developed with experts from our global Cochrane network, they are based on World Health Organization interim guidance, and continuously updated.

Coming up…

Like the reviews themselves, we update our blogs to reflect the latest evidence. There are new reviews coming up, as well as updates of existing reviews, so check back for additions to this blog.

Keeping up to date

As well as coming back to this blog, you can find Cochrane resources and news on COVID-19 here and this will also be continually updated.

References (pdf)

Join in the conversation on Twitter with @CochraneUK @SarahChapman30 or leave a comment on the blog. Please note, we will not publish comments that link to commercial sites or appear to endorse commercial products. We welcome diverse views and encourage discussion but ask that comments are respectful and reserve the right to not publish comments we consider offensive.

Sarah Chapman has nothing to disclose.

Editor’s note: This blog was last updated on 05 January 2021

COVID-19 evidence: a Cochrane round-up by Sarah Chapman

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