Vaccine effectiveness studies have conclusively demonstrated the benefit of COVID-19 vaccines in reducing individual symptomatic and severe disease, resulting in reduced hospitalisations and intensive care unit admissions.
1
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add advertising here- Thompson MG
- Stenehjem E
- Grannis S
- et al.
Effectiveness of COVID-19 vaccines in ambulatory and inpatient care settings.
However, the impact of vaccination on transmissibility of SARS-CoV-2 needs to be elucidated. A prospective cohort study in the UK by Anika Singanayagam and colleagues
2
- Singanayaman A
- Hakki S
- Dunning J
- et al.
Community transmission and viral load kinetics of the SARS-CoV-2 delta (B.1.617.2) variant in vaccinated and unvaccinated individuals in the UK: a prospective, longitudinal, cohort study.
regarding community transmission of SARS-CoV-2 among unvaccinated and vaccinated individuals provides important information that needs to be considered in reassessing vaccination policies. This study showed that the impact of vaccination on community transmission of circulating variants of SARS-CoV-2 appeared to be not significantly different from the impact among unvaccinated people.
2
- Singanayaman A
- Hakki S
- Dunning J
- et al.
Community transmission and viral load kinetics of the SARS-CoV-2 delta (B.1.617.2) variant in vaccinated and unvaccinated individuals in the UK: a prospective, longitudinal, cohort study.
,
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add advertising here3
- Wilder-Smith A
What is the vaccine effect on reducing transmission in the context of the SARS-CoV-2 delta variant?.
The scientific rationale for mandatory vaccination in the USA relies on the premise that vaccination prevents transmission to others, resulting in a “pandemic of the unvaccinated”.
4
- Tayag Y
Stop calling it a pandemic of the unvaccinated. The Atlantic.
Yet, the demonstration of COVID-19 breakthrough infections among fully vaccinated health-care workers (HCW) in Israel, who in turn may transmit this infection to their patients,
5
- Bergwerk M
- Gonen T
- Lustig Y
- et al.
COVID-19 breakthrough infections in vaccinated health care workers.
requires a reassessment of compulsory vaccination policies leading to the job dismissal of unvaccinated HCW in the USA. Indeed, there is growing evidence that peak viral titres in the upper airways of the lungs and culturable virus are similar in vaccinated and unvaccinated individuals.2,3,5–7 A recent investigation by the US Centers for Disease Control and Prevention of an outbreak of COVID-19 in a prison in Texas showed the equal presence of infectious virus in the nasopharynx of vaccinated and unvaccinated individuals.
6
- Hagan LM
- McCormick DW
- Lee C
- et al.
Outbreak of SARS-CoV-2 B.1.617.2 (delta) variant infections among incarcerated persons in a federal prison—Texas, July–August 2021.
Similarly, researchers in California observed no major differences between vaccinated and unvaccinated individuals in terms of SARS-CoV-2 viral loads in the nasopharynx, even in those with proven asymptomatic infection.
7
- Acharya CB
- Schrom J
- Mitchell AM
- et al.
No significant difference in viral load between vaccinated and unvaccinated, asymptomatic and symptomatic groups infected with SARS-CoV-2 delta variant.
Thus, the current evidence suggests that current mandatory vaccination policies might need to be reconsidered, and that vaccination status should not replace mitigation practices such as mask wearing, physical distancing, and contact-tracing investigations, even within highly vaccinated populations.
I declare no competing interests.
References
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Effectiveness of COVID-19 vaccines in ambulatory and inpatient care settings.
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- Singanayaman A
- Hakki S
- Dunning J
- et al.
Community transmission and viral load kinetics of the SARS-CoV-2 delta (B.1.617.2) variant in vaccinated and unvaccinated individuals in the UK: a prospective, longitudinal, cohort study.
Lancet Infect Dis. 2021; ()
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- Wilder-Smith A
What is the vaccine effect on reducing transmission in the context of the SARS-CoV-2 delta variant?.
Lancet Infect Dis. 2021; ()
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Stop calling it a pandemic of the unvaccinated. The Atlantic.
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- Lustig Y
- et al.
COVID-19 breakthrough infections in vaccinated health care workers.
N Engl J Med. 2021; 385: 1474-1484
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- McCormick DW
- Lee C
- et al.
Outbreak of SARS-CoV-2 B.1.617.2 (delta) variant infections among incarcerated persons in a federal prison—Texas, July–August 2021.
MMWR Morb Mortal Wkly Rep. 2021; 70: 1349-1354
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- Acharya CB
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No significant difference in viral load between vaccinated and unvaccinated, asymptomatic and symptomatic groups infected with SARS-CoV-2 delta variant.
medRvix. 2021; ()
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DOI: https://doi.org/10.1016/S1473-3099(21)00768-4
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© 2021 Elsevier Ltd. All rights reserved.
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- Transmissibility of SARS-CoV-2 among fully vaccinated individuals
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The important analysis by Anika Singanayagam and colleagues1 demonstrated that individuals fully vaccinated against SARS-CoV-2 with breakthrough infections have similar peak viral loads to unvaccinated people and might infect other fully vaccinated individuals within the same household. Of particular concern, vaccines that permit transmission do not confer sterilising immunity, thus potentially resulting in accumulation of large viral loads and increased risk of immune escape.2 By mainly targeting the SARS-CoV-2 spike protein, vaccines can favour propagation of variants with immune-escape mutations.
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Vaccination reduces the risk of delta variant infection and accelerates viral clearance. Nonetheless, fully vaccinated individuals with breakthrough infections have peak viral load similar to unvaccinated cases and can efficiently transmit infection in household settings, including to fully vaccinated contacts. Host–virus interactions early in infection may shape the entire viral trajectory.
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We thank Carlos Franco-Peredes, Mirjam Knol and colleagues, and Humphrey Ko for their interest in our Article.1 We reported that one in four household contacts exposed to fully vaccinated index cases with breakthrough delta (B.1.617.2)-variant infections, and one in four fully vaccinated household contacts exposed to delta-infected index cases, become infected. These are appreciable risks, which led us to conclude that fully vaccinated individuals remain susceptible to infection and, when breakthrough infection occurs, can efficiently transmit infection in household settings.
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