Response to: COVID-19 re-infection. Vaccinated individuals as a potential source of transmission

Future trajectory of SARS-CoV-2: Constant spillover back and forth between humans and animals

SARS-CoV-2, known as severe acute respiratory syndrome coronavirus 2, is causing a massive global public health dilemma. In particular, the outbreak of the Omicron variants of SARS-CoV-2 in several countries has aroused the great attention of the World Health Organization (WHO). As of February 1st, 2023, the WHO had counted 671,016,135 confirmed cases and 6,835,595 deaths worldwide. Despite effective vaccines and drug treatments, there is currently no way to completely and directly eliminate SARS-CoV-2. Moreover, frequent cases of SARS-CoV-2 infection in animals have also been reported. In this review, we suggest that SARS-CoV-2, as a zoonotic virus, may be frequently transmitted between animals and humans in the future, which provides a reference and warning for rational prevention and control of COVID-19.

Nosocomial Transmission of SARS-CoV-2 Involving Vaccinated Health Care Workers

COVID-19 vaccination has proven to be effective at preventing symptomatic disease but there are scarce data to fully understand whether vaccinated individuals can still behave as SARS-CoV-2 transmission vectors. Based on viral genome sequencing and detailed epidemiological interviews, we report a nosocomial transmission event involving two vaccinated health care-workers (HCWs) and four patients, one of them with fatal outcome. Strict transmission control measures, as during the prevaccination period, must be kept between HCWs and HCWs-patients in nosocomial settings. IMPORTANCE COVID-19 vaccination has proven to be effective at preventing symptomatic disease. Although some transmission events involving vaccinated cases have also been reported, scarce information is still available to fully understand whether vaccinated individuals may still behave as vectors in SARS-CoV-2 transmission events. Here, we report a SARS-CoV-2 nosocomial transmission event, supported on whole genome sequencing, in early March 2021 involving two vaccinated HCWs and four patients in our institution. Strict transmission control measures between HCWs and HCWs - patients in nosocomial settings must not be relaxed, and should be kept as strictly as during the prevaccination period.

Nature of Acquired Immune Responses, Epitope Specificity and Resultant Protection from SARS-CoV-2

The primary global response to the SARS-CoV-2 pandemic has been to bring to the clinic as rapidly as possible a number of vaccines that are predicted to enhance immunity to this viral infection. While the rapidity with which these vaccines have been developed and tested (at least for short-term efficacy and safety) is commendable, it should be acknowledged that this has occurred despite the lack of research into, and understanding of, the immune elements important for natural host protection against the virus, making this endeavor a somewhat unique one in medical history. In contrast, as pointed out in the review below, there were already important past observations that suggested that respiratory infections at mucosal surfaces were susceptible to immune clearance by mechanisms not typical of infections caused by systemic (blood-borne) pathogens. Accordingly, it was likely to be important to understand the role for both innate and acquired immunity in response to viral infection, as well as the optimum acquired immune resistance mechanisms for viral clearance (B cell or antibody-mediated, versus T cell mediated). This information was needed both to guide vaccine development and to monitor its success. We have known that many pathogens enter into a quasi-symbiotic relationship with the host, with each undergoing sequential change in response to alterations the other makes to its presence. The subsequent evolution of viral variants which has caused such widespread concern over the last 3-6 months as host immunity develops was an entirely predictable response. What is still not known is whether there will be other unexpected side-effects of the deployment of novel vaccines in humans which have yet to be characterized, and, if so, how and if these can be avoided. We conclude by remarking that to ignore a substantial body of well-attested immunological research in favour of expediency is a poor way to proceed.

Symptomatic SARS-CoV-2 infections after full schedule BNT162b2 vaccination in seropositive healthcare workers: a case series from a single institution

We report 11 cases of SARS-CoV-2 infection in healthcare workers (HCW) naïve for COVID-19 and seropositive after the second dose of the BNT162b2 mRNA vaccine. Based on voluntary-based surveillance, they tested positive for different strains of SARS-CoV-2, as Spike gene sequencing showed. Five of them reported mild symptoms. Given the risk for SARS-CoV-2 introduction from asymptomatic vaccinees, this case series suggests the need to continue nasopharyngeal screening programmes.