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Effect of Covid-19 Vaccination on Transmission of Alpha and Delta Variants.
N Engl J Med. 2022 02 24; 386(8):744-756.NEJM

Abstract

BACKGROUND

Before the emergence of the B.1.617.2 (delta) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), vaccination reduced transmission of SARS-CoV-2 from vaccinated persons who became infected, potentially by reducing viral loads. Although vaccination still lowers the risk of infection, similar viral loads in vaccinated and unvaccinated persons who are infected with the delta variant call into question the degree to which vaccination prevents transmission.

METHODS

We used contact-testing data from England to perform a retrospective observational cohort study involving adult contacts of SARS-CoV-2-infected adult index patients. We used multivariable Poisson regression to investigate associations between transmission and the vaccination status of index patients and contacts and to determine how these associations varied with the B.1.1.7 (alpha) and delta variants and time since the second vaccination.

RESULTS

Among 146,243 tested contacts of 108,498 index patients, 54,667 (37%) had positive SARS-CoV-2 polymerase-chain-reaction (PCR) tests. In index patients who became infected with the alpha variant, two vaccinations with either BNT162b2 or ChAdOx1 nCoV-19 (also known as AZD1222), as compared with no vaccination, were independently associated with reduced PCR positivity in contacts (adjusted rate ratio with BNT162b2, 0.32; 95% confidence interval [CI], 0.21 to 0.48; and with ChAdOx1 nCoV-19, 0.48; 95% CI, 0.30 to 0.78). Vaccine-associated reductions in transmission of the delta variant were smaller than those with the alpha variant, and reductions in transmission of the delta variant after two BNT162b2 vaccinations were greater (adjusted rate ratio for the comparison with no vaccination, 0.50; 95% CI, 0.39 to 0.65) than after two ChAdOx1 nCoV-19 vaccinations (adjusted rate ratio, 0.76; 95% CI, 0.70 to 0.82). Variation in cycle-threshold (Ct) values (indicative of viral load) in index patients explained 7 to 23% of vaccine-associated reductions in transmission of the two variants. The reductions in transmission of the delta variant declined over time after the second vaccination, reaching levels that were similar to those in unvaccinated persons by 12 weeks in index patients who had received ChAdOx1 nCoV-19 and attenuating substantially in those who had received BNT162b2. Protection in contacts also declined in the 3-month period after the second vaccination.

CONCLUSIONS

Vaccination was associated with a smaller reduction in transmission of the delta variant than of the alpha variant, and the effects of vaccination decreased over time. PCR Ct values at diagnosis of the index patient only partially explained decreased transmission. (Funded by the U.K. Government Department of Health and Social Care and others.).

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Authors+Show Affiliations

Eyre DW
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.
Taylor D
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.
Purver M
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.
Chapman D
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.
Fowler T
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.
Pouwels KB
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.
Walker AS
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.
Peto TEA
From the Big Data Institute (D.W.E.) and the Health Economics Research Centre (K.B.P.), the Nuffield Department of Population Health, National Institute for Health Research Health Protection Research Unit in Healthcare Associated Infections and Antimicrobial Resistance (D.W.E., K.B.P., A.S.W., T.E.A.P.), and the Nuffield Department of Medicine (A.S.W., T.E.A.P.), University of Oxford, Oxford, and the Department of Health and Social Care, National Health Service Test and Trace (D.T., M.P., T.F.), Deloitte MCS (D.C.), and William Harvey Research Institute, Queen Mary University of London (T.F.), London - all in the United Kingdom.

MeSH

AdultAgedAged, 80 and overBNT162 VaccineCOVID-19COVID-19 Nucleic Acid TestingChAdOx1 nCoV-19Disease Transmission, InfectiousEnglandFemaleHumansMaleMiddle AgedRetrospective StudiesSARS-CoV-2Viral Load

Pub Type(s)

Journal Article
Observational Study
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

34986294

Citation

Eyre, David W., et al. "Effect of Covid-19 Vaccination On Transmission of Alpha and Delta Variants." The New England Journal of Medicine, vol. 386, no. 8, 2022, pp. 744-756.
Eyre DW, Taylor D, Purver M, et al. Effect of Covid-19 Vaccination on Transmission of Alpha and Delta Variants. N Engl J Med. 2022;386(8):744-756.
Eyre, D. W., Taylor, D., Purver, M., Chapman, D., Fowler, T., Pouwels, K. B., Walker, A. S., & Peto, T. E. A. (2022). Effect of Covid-19 Vaccination on Transmission of Alpha and Delta Variants. The New England Journal of Medicine, 386(8), 744-756. https://doi.org/10.1056/NEJMoa2116597
Eyre DW, et al. Effect of Covid-19 Vaccination On Transmission of Alpha and Delta Variants. N Engl J Med. 2022 02 24;386(8):744-756. PubMed PMID: 34986294.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effect of Covid-19 Vaccination on Transmission of Alpha and Delta Variants. AU - Eyre,David W, AU - Taylor,Donald, AU - Purver,Mark, AU - Chapman,David, AU - Fowler,Tom, AU - Pouwels,Koen B, AU - Walker,A Sarah, AU - Peto,Tim E A, Y1 - 2022/01/05/ PY - 2022/1/6/pubmed PY - 2022/3/3/medline PY - 2022/1/5/entrez SP - 744 EP - 756 JF - The New England journal of medicine JO - N Engl J Med VL - 386 IS - 8 N2 - BACKGROUND: Before the emergence of the B.1.617.2 (delta) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), vaccination reduced transmission of SARS-CoV-2 from vaccinated persons who became infected, potentially by reducing viral loads. Although vaccination still lowers the risk of infection, similar viral loads in vaccinated and unvaccinated persons who are infected with the delta variant call into question the degree to which vaccination prevents transmission. METHODS: We used contact-testing data from England to perform a retrospective observational cohort study involving adult contacts of SARS-CoV-2-infected adult index patients. We used multivariable Poisson regression to investigate associations between transmission and the vaccination status of index patients and contacts and to determine how these associations varied with the B.1.1.7 (alpha) and delta variants and time since the second vaccination. RESULTS: Among 146,243 tested contacts of 108,498 index patients, 54,667 (37%) had positive SARS-CoV-2 polymerase-chain-reaction (PCR) tests. In index patients who became infected with the alpha variant, two vaccinations with either BNT162b2 or ChAdOx1 nCoV-19 (also known as AZD1222), as compared with no vaccination, were independently associated with reduced PCR positivity in contacts (adjusted rate ratio with BNT162b2, 0.32; 95% confidence interval [CI], 0.21 to 0.48; and with ChAdOx1 nCoV-19, 0.48; 95% CI, 0.30 to 0.78). Vaccine-associated reductions in transmission of the delta variant were smaller than those with the alpha variant, and reductions in transmission of the delta variant after two BNT162b2 vaccinations were greater (adjusted rate ratio for the comparison with no vaccination, 0.50; 95% CI, 0.39 to 0.65) than after two ChAdOx1 nCoV-19 vaccinations (adjusted rate ratio, 0.76; 95% CI, 0.70 to 0.82). Variation in cycle-threshold (Ct) values (indicative of viral load) in index patients explained 7 to 23% of vaccine-associated reductions in transmission of the two variants. The reductions in transmission of the delta variant declined over time after the second vaccination, reaching levels that were similar to those in unvaccinated persons by 12 weeks in index patients who had received ChAdOx1 nCoV-19 and attenuating substantially in those who had received BNT162b2. Protection in contacts also declined in the 3-month period after the second vaccination. CONCLUSIONS: Vaccination was associated with a smaller reduction in transmission of the delta variant than of the alpha variant, and the effects of vaccination decreased over time. PCR Ct values at diagnosis of the index patient only partially explained decreased transmission. (Funded by the U.K. Government Department of Health and Social Care and others.). SN - 1533-4406 UR - https://www.unboundmedicine.com/medline/citation/34986294/Effect_of_Covid_19_Vaccination_on_Transmission_of_Alpha_and_Delta_Variants_ DB - PRIME DP - Unbound Medicine ER -