Vaccination[/B] against COVID-19 reduces the transmission potential of SARS-CoV-2 probably by reducing the viral load of vaccinated patients with COVID-19, however these data are based on data prior to the global prevalence of the Delta strain.
Physicians from the Therapeutic Clinic of the Medical School of the National and Kapodistrian University of Athens Theodora Psaltopoulou, Yannis Danasis, Panos Malandrakis and Thanos Dimopoulos (Dean of EKPA) summarize the findings from the recent publication of David W. Eyre and colleagues in the prestigious journal The New England Journal of Medicine (DOI: 10.1056/NEJMoa2116597).
What the study showed
The researchers used contact tracing data from patients with COVID-19 in the UK and conducted a retrospective observational study in adults.
M146,243 contacts with 108,498 initial patients diagnosed with COVID-19 were studied. Of these, 37% (54,667 individuals) showed positive molecular testing (PCR) against SARS-CoV-2.
Among initial patients with COVID-19 due to the SARS-CoV-2 alpha strain, vaccination with two doses of BNT162b2 or AZD1222 was associated with a reduced likelihood of positive PCR at contacts compared with unvaccinated patients (68% for BNT162b2 and 52% for AZD1222). The corresponding percentages were lower for initial COVID-19 patients infected with the Delta strain.
More specifically, vaccination with two doses of BNT162b2 was associated with a 50% reduced probability of positive PCR at contacts compared to unvaccinated patients, whereas vaccination with two doses of AZD1222 was associated with a 24% reduced probability. Furthermore, it was estimated that differences in viral load of initial COVID-19 patients based on PCR-positive cycles (Ct) could explain less than a quarter of the differences in vaccine protection rates between the two strains.
In addition, the reduction in Delta strain transmissibility showed attenuation over time since the second dose of the vaccine, especially for those vaccinated with AZD1222 and 3 months after the second dose.
Regarding the effect of vaccination on contacts of initial patients with COVID-19, those fully vaccinated who had contacted a case were less likely to have a positive PCR (17% BNT162b2, 22% AZD1222) compared to unvaccinated (52%). Protection declined at 3 months after the second dose of vaccine.
These data support the administration of a booster dose of COVID-19 vaccine to maintain a high level of protection against SARS-CoV-2.
Source: in.gr
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