Are COVID-19 vaccines effective and safe? New Cochrane evidence

In this blog, Sarah Chapman from Cochrane UK looks at the new evidence from Cochrane on COVID-19 vaccines.

 Take-home points

Take-home points: Cochrane evidence shows that most COVID-19 vaccines protect against infection and severe or critical illness caused by the virus For most of the vaccines investigated, more people who had been vaccinated reported localised or temporary side effects compared to those who had no treatment or placebo The review is part of the COVID-NMA initiative, supported by the World Health Organization and Cochrane, which provides live mapping and evidence synthesis of COVID-19 trials to help decision-makers

It’s three years since COVID-19 was first reported. Since then, almost 80% of us in the UK (70% worldwide) have had at least one dose of a COVID-19 vaccine and just over 75% (65% worldwide) have been fully vaccinated. The rapid development of several effective vaccines against SARS-CoV-2 , a previously unknown virus, is surely a major success story. A new Cochrane Review Efficacy and safety of COVID-19 vaccines (published December 2022) now brings together the best available evidence on the effectiveness and safety of a number of these.

The Cochrane Review authors wanted to find out how well COVID-19 vaccines work in reducing the following: infection with the virus, disease with symptoms, severe disease, and the number of deaths from any cause. They also wanted to know about vaccine safety.

They looked for studies of randomized controlled trials comparing COVID-19 vaccines with each other, with placebo (a sham vaccine – it looks the same but has no active ingredient), or with no vaccine.

They were able to include 41 studies of over almost 434,000 people, assessing 12 vaccines, including full primary vaccination series and booster doses. Most studies compared a vaccine with placebo, only have short-term results (most only two months after full vaccination), and were done before ‘variants of concern’ appeared.

The evidence may not apply to everyone.  Because they were excluded from taking part in the trials, it’s not possible to say that the results of the review apply to pregnant women, people with weakened immune systems or people who have had COVID-19 before.

What the evidence shows about how well COVID-19 vaccines work

 Most vaccines reduce or probably reduce the risk of getting COVID-19, compared with placebo: Pfizer/BioNTech, Moderna, CureVac COVID-19, Oxford-AstraZeneca, Janssen, Sputnik V (Gam-COVID-Vac),Sinopharm (WIBP CorV and BBIBP-CorV), Bharat (Covaxin), Novavax and Soberana 2 (Finlay-FR-2).

These vaccines reduced or probably reduced the risk of severe or critical illness: Pfizer/BioNTech, Moderna, Janssen, Sputnik V, Bharat and Novavax.

 The evidence on deaths from any cause is uncertain for most vaccines, as very few deaths were reported during the trials.

What evidence is there about the safety of COVID-19?

 There is evidence that, unsurprisingly, more people who had been vaccinated reported side effects than those who had been given a placebo or had no treatment. These side effects included feeling sick, tiredness, headache, chills, fever and muscle pains. They are usually mild and don’t last long.

As for serious harms, the review authors conclude “there is probably little or no difference between most vaccines and placebo”.

What next for research on COVID-19 vaccines?

 There is a lot that we still need to know, including the effectiveness and safety of the vaccines in different groups of people (like pregnant women) and against variants of concern; how new vaccines compare with existing ones and how to overcome the problem of vaccine effectiveness wearing off over time. We also need to know more about vaccine schedules, and about their effect on other outcomes, such as preventing long COVID-19.

Keeping up with new evidence

There are many trials of COVID-19 vaccines happening (more than 600 randomised trials have been registered) and the evidence base is changing rapidly. This review is part of a bigger project, the COVID-NMA initiative. Results are made available and updated on their website every two weeks, providing decision-makers with an up-to-date mapping and synthesis of evidence on this and other interventions for preventing and treating COVID-19.

This review will be updated at least twice a year, or sooner if new evidence changes the conclusions or the certainty of the evidence.

Find out more

NHS pages on Coronavirus (COVID-19) vaccine

Evidently Cochrane blogs on COVID-19 evidence can be found here and include blogs on COVID tests: how accurate are LFTs? Treatments for mild COVID-19; Treatments for moderate to severe COVID-19; and COVID-19 evidence: a Cochrane round-up.

The Cochrane Review:

Plain Language Summary – What are the benefit and risks of vaccines for preventing COVID-19?

Full review – Graña C, Ghosn L, Evrenoglou T, Jarde A, Minozzi S, Bergman H, Buckley BS, Probyn K, Villanueva G, Henschke N, Bonnet H, Assi R, Menon S, Marti M, Devane D, Mallon P, Lelievre J-D, Askie LM, Kredo T, Ferrand G, Davidson M, Riveros C, Tovey D, Meerpohl JJ, Grasselli G, Rada G, Hróbjartsson A, Ravaud P, Chaimani A, Boutron I. Efficacy and safety of COVID-19 vaccines. Cochrane Database of Systematic Reviews 2022, Issue 12. Art. No.: CD015477. DOI: 10.1002/14651858.CD015477.

Press release 07 December 2022 Cochrane Review of COVID-19 vaccines shows they are effective.

You can join in the conversation on Twitter with @SarahChapman30 @CochraneUK or leave a comment on the blog.

Please note, we cannot give specific medical advice and do not publish comments that link to individual pages requesting donations or to commercial sites, or appear to endorse commercial products. We welcome diverse views and encourage discussion but we ask that comments are respectful and reserve the right to not publish any we consider offensive. Cochrane UK does not fact check – or endorse – readers’ comments, including any treatments mentioned.

Sarah Chapman has nothing to disclose.


Are COVID-19 vaccines effective and safe? New Cochrane evidence by Sarah Chapman

is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International

3 Comments on this post

  1. I used to think of the Cochrane as a Gold standard. But it’s becoming clear that they are losing their capability of reviewing the science in a manner that’s congruent with the scientific method. Are you morphing into another bought and paid for organisation?

    keith littlewood / Reply
  2. […] they were getting a much milder case than they would have if they weren’t vaxxed. (See e.g., here but note link to W.H.O.) You can’t really argue that isn’t true, but therein lies the problem. […]

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