In the United States, the US Food and Drug Administration (FDA) has approved two mRNA-based COVID-19 vaccines developed by Pfizer/BioNTech and Moderna, which have shown high efficacy against SARS-CoV-2 infection and COVID-19 disease in clinical trials. However, the ability to vaccinate a large part of the global population is limited by vaccine supply. In order to ensure fair access to vaccines throughout the world, the COVID-19 vaccines Global Access (COVAX) initiative was launched. In many countries, especially those with low socioeconomic status, there is a serious shortage of vaccines. Thus, in order to get the maximum vaccine benefits, the most vulnerable population should be prioritized for the vaccination. Currently, most countries prioritize vaccination for healthcare and other frontline workers, elderly people, and people with comorbidities.
To further narrow down the prioritization criteria, scientists from the Cleveland Clinic, USA, have recently evaluated the effectiveness of COVID-19 vaccination among individuals with or without a history of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The study findings reveal that individuals with previous SARS-CoV-2 infection do not get additional benefits from vaccination, indicating that COVID-19 vaccines should be prioritized to individuals without prior infection. The study is currently available on the medRxiv* preprint server.bThe study was conducted on 52,238 employees in the Cleveland Clinic. A positive RT-PCR test was considered to define SARS-CoV-2 infection. The participants received two doses of the Pfizer/BioNTech or Moderna COVID-19 vaccine at an interval of 28 days. A participant was considered vaccinated after 14 days of receiving the 2nd vaccine dose. Similarly, a participant who tested positive for SARS-CoV-2 at least 42 days before the vaccination initiation was considered previously infected.
Of all enrolled participants, 5% had previous SARS-CoV-2 infection. Compared to 59% of non-infected participants, only 47% of previously infected participants were vaccinated by the end of the study. About 63% of all vaccinated participants received the Moderna vaccine. The analysis of cumulative COVID-19 incidence revealed that during the course of the study, SARS-CoV-2 infection occurred almost exclusively in participants who were not previously infected and were not vaccinated. Interestingly, no significant difference in COVID-19 incidence was observed between previously infected and currently unvaccinated participants, previously infected and currently vaccinated participants, and previously uninfected and currently vaccinated participants. The participants from these three groups exhibited a significantly lower incidence of SARS-CoV-2 infection compared to previously uninfected and currently unvaccinated participants.
Specifically, of all infections during the study period, 99.3% occurred in participants who were not infected previously and remained unvaccinated. In contrast, only 0.7% of infections occurred in participants who were not previously infected but were currently vaccinated. Importantly, not a single incidence of SARS-CoV-2 infection was observed in previously infected participants with or without vaccination. With further statistical analysis, it was observed that the COVID-19 vaccination significantly reduced the risk of SARS-CoV-2 infection in previously uninfected participants but not in previously infected participants. Although the study did not directly estimate the duration of protection from natural infection, it was observed that previously infected participants remained protected against COVID-19 for at least 10 months after the symptom onset or a positive test result. This is a preliminary study to be evaluated, but who knows what the increase in knowledge may reserve to optimize not only the limitation of infections, but also the possibility of carrying out a more targeted vaccination campaign.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific references
Shrestha NK et al. medRxiv 2021 Jun 1: 21258176.
Dott. Gianfrancesco Cormaci
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