A systematic review of COVID-19 vaccine efficacy and effectiveness against SARS-CoV-2 infection and disease

Abstract

Billions of doses of COVID-19 vaccines have been administered around the world, dramatically reducing SARS-CoV-2 incidence in some settings. Many studies suggest vaccines provide a high degree of protection against infection and disease, but precise estimates vary and studies differ in design, outcomes measured, dosing regime, location, and circulating virus strains. Here we conduct a systematic review of COVID-19 vaccines as of August 2021. We included efficacy data from Phase 3 clinical trials for 13 vaccines within the WHO Emergency Use Listing evaluation process and real-world effectiveness for 5 vaccines with observational studies meeting inclusion criteria. Vaccine metrics collected include effects against asymptomatic infection, any infection, symptomatic COVID-19, and severe outcomes including hospitalization and death, for both partial and complete vaccination, and against SARS-CoV-2 variants of concern. In addition, we review the epidemiological principles behind the design and interpretation of vaccine effects, and explain important sources of heterogeneity between studies.

COVID-19 vaccine strategies must focus on severe disease and global equity

“…A systematic review including studies up to mid-August, 2021, identified 21 efficacy trials and 58 vaccine effectiveness studies of COVID-19 vaccines, most from high-income countries. 19 Despite the short time window of 21 days between first and second doses used in vaccine trials and by many countries, single-dose efficacy and effectiveness against severe disease for mRNA (60–90% for BNT162b2; 75–80% for mRNA1273) and adenoviral vector vaccines (75–100% for ChAdOx1; 85% for Ad26.COV2) was high, but lower for inactivated viral vaccines (37–46% for CoronaVac). 19 In Canada, where longer intervals to the second dose were routine, first dose vaccine effectiveness of mRNA vaccines was highest more than 35 days after receipt in all age groups.…”

“… 19 Despite the short time window of 21 days between first and second doses used in vaccine trials and by many countries, single-dose efficacy and effectiveness against severe disease for mRNA (60–90% for BNT162b2; 75–80% for mRNA1273) and adenoviral vector vaccines (75–100% for ChAdOx1; 85% for Ad26.COV2) was high, but lower for inactivated viral vaccines (37–46% for CoronaVac). 19 In Canada, where longer intervals to the second dose were routine, first dose vaccine effectiveness of mRNA vaccines was highest more than 35 days after receipt in all age groups. 20 Another Canadian study found high vaccine effectiveness was maintained up to 4 months after a single dose of an mRNA vaccine.…”

“… 23 Most vaccine effectiveness studies, and all but one efficacy trial, were during periods when variants of concern other than delta predominated. 19 Observational studies from Ontario, Canada, 24 and England 25 found high single-dose vaccine effectiveness against severe disease due to delta, but whether this will be applicable to omicron is unknown.…”

“…Importantly, this approach might be appropriate irrespective of HIV prevalence 38 and to all vaccine platforms except inactivated viral vaccines, which have relatively low first dose effectiveness in people who are SARS-CoV-2 infection-naive. 19 , 48…”

“…4 Omicron was detected in Africa, 4 where successive waves of SARS-CoV-2 have resulted in prevalence of past infection higher than 80% in some regions 5 and despite greatly increased global vaccine supplies, 3 the average coverage that can be achieved there in 2021 is estimated to be only 17%. 6 In 2022, we argue that COVID-19 vaccine strategies must remain focused on severe disease, and that global equity in achieving high adult coverage (ie, for those aged 18 years and older) of at least one dose is key to minimising severe COVID- 19.…”