In a recent study on The Lancet* SSRN preprint server, researchers explored the efficacy of coronavirus disease 2019 (COVID-19) vaccines in preventing long COVID symptoms.
Study: The Effectiveness of COVID-19 Vaccines to Prevent Long COVID Symptoms: Staggered Cohort Analyses of Data from the UK, Spain, and Estonia. Image credit: NiphonSubsri/Shutterstock.com
*Important notice: Preprints with The Lancet publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Background
COVID-19 vaccines have proven to be highly efficient in preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes severe illness, mortality, and transmission in communities.
However, the UK Health Security Agency (UKHSA)'s recent review suggests that the effectiveness of COVID-19 vaccines in preventing long-term symptoms is still unclear. Previous studies have not extensively examined the effectiveness of vaccination in preventing long-term complications in individuals with COVID-19.
Studies have reported mixed results regarding the effectiveness of vaccination in reducing the risk of long COVID. While some studies have shown a decrease in risk, others have only noted reductions for specific symptoms or no overall risk reduction.
About the study
Health data from three European countries were used in this study, including primary care electronic health records from UK sources of Clinical Practice Research Datalink (CPRD) GOLD and CPRD AURUM, primary care records related to hospital admissions information from the Spanish Information System for Research in Primary Care (SIDIAP), and national health insurance claims from Estonia. The data was collected routinely and was de-identified.
The study was conducted as a staggered cohort study in accordance with the vaccine rollout regulations in the UK, Spain, and Estonia, as the populations became eligible for their first COVID-19 vaccine dose at different times. Four study cohorts were created for each database/country, each representing a particular phase of the rollout of the national vaccination campaign.
The source population for the first staggered study included all adults registered in CPRD GOLD or AURUM for a minimum of 180 days. Individuals were added to study groups based on eligibility criteria evaluated separately for each study:
(1) The first cohort consisted of individuals who were 75 years old or older and had not been vaccinated against COVID-19 or had a previous COVID-19 infection at the time of enrollment. Individuals were categorized into either the vaccinated or unvaccinated group depending on whether they received their initial vaccine dose during enrollment.
(2) The second cohort comprised individuals aged 75 and above, those clinically extremely vulnerable, and individuals aged 18 and above with underlying health conditions.
(3) The third cohort included individuals aged 50 and above.
(4) The fourth cohort included individuals aged 18 years or older.
Results
The first cohort involved 1,618,395 vaccinated and 1,640,371 unvaccinated people from CPRD GOLD; 5,729,915 vaccinated and 5,860,564 unvaccinated people from CPRD AURUM; 2,744,821 vaccinated and 2,588,518 unvaccinated people from SIDIAP; and 77,603 vaccinated and 302,267 unvaccinated people from CIDIVA.
Staggered cohorts included 6% to 21%, 9% to 33%, 26% to 34%, and 31% to 39% of the four databases, respectively. The majority of vaccinated individuals received either ChAdOx1 or BNT162b2 vaccines, with 59%, 56%, 15%, and 6% receiving ChAdOx1 and 38%, 40%, 66%, and 74% receiving BNT162b2 from the four databases, respectively.
Receiving the first COVID-19 vaccine dose was linked to a decreased likelihood of developing long COVID. The meta-analytic calibrated subdistribution hazard ratios (sHR) were 0.55 for CPRD GOLD, 0.64 for CPRD AURUM, 0.84 for SIDIAP, and 0.62 for CORIVA.
Furthermore, the meta-analytic calibrated sHR was 0.66, 0.70, 0.88, and 0.62 when a definition of long COVID symptoms for ≥28 was used. The meta-analytic calibrated sHR for the correlation with "post-acute COVID-19" in CPRD AURUM and SIDIAP were 0.64 and 0.60, respectively.
The calibrated sHR for ChAdOx1 was 0.63 in CPRD GOLD, 0.71 in CPRD AURUM, and 0.84 in SIDIAP. On the other hand, the sHR for BNT162b2 was 0.49, 0.53, 0.86, and 0.63 in CPRD GOLD, CPRD AURUM, SIDIAP, and CORIVA, respectively.
Meta-analysis of multiple studies showed that the first dose of BNT162b2 had a slightly stronger preventative effect, with calibrated sHR of 0.77 in CPRD GOLD and 0.72 in CPRD AURUM.
Conclusion
The study shows that COVID-19 vaccines are clinically effective in preventing long COVID, which is another advantage of vaccination for young individuals. The study's results were consistent across populations and three European countries and remained robust despite using different definitions of long COVID and conducting sensitivity analyses.
The study contributes significant data to evaluate the advantages and disadvantages of COVID-19 vaccines.
Despite the improved understanding of the safety profile, vaccination efforts across the globe were hindered by safety concerns and the perception that younger people faced a lower risk of severe COVID-19. The researchers hope that the reported protection against long COVID will increase the vaccination rate among younger people who were previously hesitant.
*Important notice: Preprints with The Lancet publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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