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COVID-19 evidence: a Cochrane round-up

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

This blog was last updated on 17 May 2022.

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.

We have two separate blogs about the evidence on treating people with COVID-19:

On this page, there are sections on:

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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, first published in July 2020 and updated in February 2021, on the accuracy of any signs and symptoms, either alone or in combination, for diagnosing COVID‐19.

Take-home points: A Cochrane Review on the accuracy of clinical signs and symptoms for diagnosing COVID-19 has been updated, with more studies and better quality evidence. It confirms that a single symptom or sign cannot accurately diagnose COVID-19. However, loss of taste or smell, high temperature, or cough may be useful to identify people who might have COVID-19, prompting further testing. 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).

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

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 point-of-care tests for diagnosing COVID-19 infection

Tests for diagnosing COVID-19 infection are important tools for helping reduce the spread of infection in communities, schools and workplaces, and have received a huge amount of attention in the press and on social media over the last year. The Cochrane Review Rapid, point‐of‐care antigen and molecular‐based tests for diagnosis of SARS‐CoV‐2 infection, was updated for the first time in March 2021. The review looks at two types of test, antigen tests (including lateral flow tests or LFTs) and molecular tests. Both types of test use swab samples taken from the nose or throat, can be used outside of a specialist laboratory and provide results in less than two hours.

Lead author, Jac Dinnes, has written a blog Rapid point-of-care tests for diagnosing COVID-19 infection: the latest Cochrane evidence to help health care professionals and members of the public interpret the evidence for their accuracy.

Most of the evidence for the diagnostic accuracy of lateral flow tests (LFTs) for COVID-19 is based on studies in people with symptoms, but there is good reason to suspect that LFTs are not as accurate when used in people without symptoms The balance of benefits and harms from using LFTs changes depending on the number of people who really have COVID-19 infection in the populations being tested (prevalence) Decisions to implement lateral flow testing should be informed by the best available evidence for how well tests perform in different populations and testing scenarios

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 has been updated, for a third time, in May 2022. It brings together evidence on the accuracy of chest (thoracic) imaging (computed tomography (CT), X‐ray and ultrasound) in diagnosing COVID‐19 in people with suspected infection. The review also considers the accuracy of chest imaging for screening asymptomatic people.

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.

Screening people with suspected COVID-19

The review includes 94 studies with 37,631 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.

Chest CT: in people with suspected COVID

  • Chest CT correctly diagnosed COVID‐19 in 87% of people who had COVID‐19.
  • However, it incorrectly identified COVID‐19 in 21% of people who did not have COVID‐19.

Chest X‐ray: in people with suspected COVID

  • Chest X‐ray correctly diagnosed COVID‐19 in 73% of people who had COVID‐19.
  • However, it incorrectly identified COVID‐19 in 27% of people who did not have COVID‐19.

Lung ultrasound: in people with suspected COVID

  • Lung ultrasound correctly diagnosed COVID‐19 in 87% of people with COVID‐19.
  • However, it incorrectly diagnosed COVID‐19 in 24% of people who did not have COVID‐19.

Screening asymptomatic people

The review also included 10 studies with 3548 people who had no symptoms (asymptomatic), of whom 364 (10%) had a final diagnosis of COVID‐19.

The results suggest CT correctly diagnosed COVID‐19 in only 56% of people who actually had COVID‐19 and incorrectly identified COVID‐19 in 8% of people who did not have COVID‐19.

Overall, the evidence so far suggests that chest CT and ultrasound are better at ruling out COVID-19 infection than distinguishing it from other respiratory problems. So, their usefulness may be limited to excluding COVID‐19 infection rather than distinguishing it from other causes of lung infection. In addition, chest imaging may only correctly diagnose COVID-19 in just over half of asymptomatic people who do actually have COVID. The authors’ confidence in the evidence is limited because the studies differed from each other, used different methods to report their results and very few studies directly compared one type of imaging test with another.

 

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 is important to have evidence of the effectiveness of these different measures to inform policy and practice.

A Cochrane Review (published in January 2022) explored the potential benefits and harms of measures implemented in the school setting to contain the COVID‐19 pandemic.

The key messages are that:

“Reopening schools or keeping schools open while having a broad range of measures in place can reduce transmission of the virus that causes COVID‐19. Such measures can also reduce the number of people who will need to go to hospital due to developing COVID‐19. We still know very little about other consequences of these measures, such as those linked to education, resources, and physical or mental health, as this knowledge is mostly based on studies modelling the real world. More studies set in the real world using real‐world data are needed.”

See also:

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.

Preventing or reducing COVID-19 infections in long term care facilities (care homes)

A Cochrane Review ‘Can non‐medicinal measures prevent or reduce SARS‐CoV‐2 infections in long term care facilities?’ (published September 2021) included 22 studies exploring this question. 11 of the studies were observational, i.e. they used real-world data, and 11 were modelling studies, i.e. they used mathematical prediction.

There were four main types of measures.

1) Entry regulation measures to prevent residents, staff or visitors introducing the virus into the facility

Examples include: staff confining themselves with residents, quarantine for newly‐admitted residents, testing new admissions, not allowing the admission of new residents, and preventing visitors from entering facilities.

Most studies showed such measures may be beneficial, but some studies found that there may be no little or no effect or unwanted effects, such as delirium and depression among residents when visitors were restricted.

For more information: What are the effects of COVID‐19 entry regulation measures in long‐term care facilities (LTCFs)?

2) Contact‐regulating and transmission‐reducing measures to prevent people passing on the virus

Examples include: wearing masks or personal protective equipment (PPE), social distancing, extra cleaning, reducing contact between residents and among staff, and placing residents and staff in care groups and limiting contact between groups.

Some measures may be beneficial, but the evidence is often very uncertain.

For more information: What are the effects of contact regulation and transmission‐reducing measures on COVID‐19 in long‐term care facilities (LTCFs)?

3) Surveillance measures designed to identify an outbreak early

Examples include: regular testing of residents or staff regardless of symptoms, and symptom‐based testing

Routine testing of residents and staff may reduce the number of infections, hospitalisations, and deaths among residents (although the evidence on the number of deaths among staff was less clear).

Testing more often, getting test results faster, and using more accurate tests may have more beneficial effects.

For more information: What are the effects of COVID‐19 surveillance measures in long‐term care facilities (LTCFs)?

4) Outbreak control measures to reduce the consequences of an outbreak

Examples include: isolation of infected residents, and separating infected and non‐infected residents or staff caring for them.

These measures may reduce the number of infections and the risk of outbreaks in facilities, but often the evidence is very uncertain.

For more information: What are the effects of COVID‐19 outbreak control measures in long‐term care facilities (LTCFs)?

A combination of different measures may be effective in reducing the number of infections and deaths.

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, looked at travel-related control measures to contain the COVID-19 pandemic. Not surprisingly, it highlighted uncertainty about their effectiveness and a lack of reliable and ‘real-life’ evidence. The review was updated in March 2021.

Jacob Burns, lead author of this update explains, “In this update we identified a much expanded evidence base related to international travel control measures to contain the COVID-19 pandemic, with 38 additional studies focusing on COVID-19 identified. Many of the studies were similar with regard to scope and methods, and overall the conclusions of the updated review remain largely the same. Some aspects of the evidence base, however, were improved – for example, we identified studies from further parts of the world that were not represented in the original review, including African and Eastern Mediterranean regions. Additionally, we identified more studies evaluating entry and/or exit screening measures at real-world ports of entry.” 

You can read about the review in this blog “Travel-related measures for controlling the spread of COVID-19: New Cochrane evidence“.

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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. Preventing and treating persistent symptoms after COVID-19 infection

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Preventing and treating persistent symptoms after COVID-19 infection

Persistent problems with sense of smell after COVID-19 infection

A Cochrane Review on Interventions for the prevention of persistent smell disorders (olfactory dysfunction) after COVID‐19 infection and another on Interventions for the treatment of persistent smell disorders after COVID‐19 infection were published in July 2020. They each include only one small study and highlight current uncertainty about how to prevent or treat ongoing problems with sense of smell after COVID-19. However, the review authors found that there are studies being done at the moment and will be able to assess these for inclusion in updates of this ‘living systematic review’, adding new research as it becomes available.

Here’s what they found:

Interventions for the prevention of persistent smell disorders (olfactory dysfunction) after COVID‐19 infection: The potential benefits and harms of interventions to prevent problems with sense of smell (reduced, changed or lost sense of smell) from lasting weeks or months after COVID-19 infection are very uncertain. EVIDENCE GAP. Cochrane Review (published July 2021): one study with 100 people with problems with their sense of smell that started after a COVID-19 infection and had lasted less than four weeks at the start of the study. It compared a steroid spray that goes into the nose with no treatment. Everyone taking part in the study was asked to to spend a short time each day practising smelling particular scents, to try and stimulate their sense of smell to return. This is a living systematic review, which will include new evidence as it becomes available.

Interventions for the treatment of persistent smell disorders (olfactory dysfunction) after COVID‐19 infection: The potential benefits and harms of treatments for problems with sense of smell (reduced, changed or lost sense of smell) that last weeks or months after COVID-19 infection are very uncertain. EVIDENCE GAP. Cochrane Review (published July 2021): one study with 18 people with problems with their sense of smell that started after a COVID-19 infection and lasted at least four weeks. It compared steroid tablets plus a nasal spray (consisting of a mix of steroids, decongestant and an agent that breaks down mucus) with no treatment. This is a living systematic review, which will include new evidence as it becomes available.

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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.

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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.

We also welcomed news (March 2021) of two new clinical trials which have been launched in the UK to investigate potential preventative treatments for the most clinically vulnerable (those with long-term underlying conditions and those in care homes) to prevent them catching COVID-19.

Keeping up to date

As well as coming back to this blog, you can find Cochrane resources and news on COVID-19 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 and Selena Ryan-Vig have nothing to disclose.


Sarah Chapman and Selena Ryan-Vig

About Sarah Chapman and Selena Ryan-Vig

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Sarah and Selena are Cochrane UK’s Knowledge Brokers. Their role involves sharing evidence in accessible ways with those who could find it helpful for their health decision-making, and encouraging engagement with it through social media. Sarah trained and worked as a nurse, has degrees in History from the Universities of Oxford and Reading, and worked in health services research before joining Cochrane UK in 2007. She lives with severe hearing loss and is a Patient Ambassador for the COACH Trial, a randomised controlled trial of cochlear implantation versus hearing aids in adults with severe hearing loss. Sarah tweets @SarahChapman30. Selena has a psychology degree from the University of Bath and has previously worked for a national charity that provides support for young women. With a colleague, Selena delivers interactive sessions to students from Years 10 to 13 to teach about evidence-based practice and to encourage critical thinking, particularly around healthcare claims made in the media.

COVID-19 evidence: a Cochrane round-up by Sarah Chapman and Selena Ryan-Vig

is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International

4 Comments on this post

  1. I can’t find any Cochrane reviews on the efficacy of various covid vaccines. Are there no reviews? Surprises me there isn’t

    Mr noodles / Reply

    • Thank you for this question, which has led us to make enquiries. We understand that a review of the COVID vaccines is being prepared and should be available soon. Meanwhile, you might wish to see the joint Cochrane and WHO COVID-19 living network meta-analysis initiative which provides living maps of evidence on preventing and treating COVID-19 and maintains living syntheses of evidence, including on vaccines, which are updated every 2 weeks.
      The living map of evidence on vaccines is here: https://covid-nma.com/vaccines/mapping/
      The living synthesis of RCT evidence on vaccine effectiveness is here: https://covid-nma.com/vaccines/
      The living synthesis of RCT evidence on vaccine effectiveness on variants of concern is here: https://covid-nma.com/vaccines/variants/
      The living synthesis of observational studies evidence on vaccine effectiveness on variants of concern is here: https://covid-nma.com/vaccines/os_vaccines/

      The Cochrane protocol for this initiative is here:

      Boutron I, Chaimani A, Devane D, Meerpohl JJ, Rada G, Hróbjartsson A, Tovey D, Grasselli G, Ravaud P. Interventions for the prevention and treatment of COVID‐19: a living mapping of research and living network meta‐analysis. Cochrane Database of Systematic Reviews 2020, Issue 11. Art. No.: CD013769. DOI: 10.1002/14651858.CD013769
      https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013769/full

      We hope this helps.
      Best wishes,
      Sarah Chapman [Editor]

      Sarah Chapman / (in reply to Mr noodles) Reply

  2. I found this blog incredibly useful to present what we have done in Cochrane and why. Thank you very much Sarah!

    Karla Soares-Weiser / Reply

  3. I liked very much those informations!

    Maria Benedita Lima Pardo / Reply

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