I’ve been hearing recently from friends and colleagues concerned about the ability of the Delta variant to cause “breakthrough infections” in those fully vaccinated and what this means.
First, almost all of the hospitalizations, intubations and deaths are now occurring in those not vaccinated. Vaccinated individuals may carry and transmit the virus, but they are not suffering serious disease, except for those with concomitant immunosuppressant conditions such as cancer, transplantation or autoimmune disease patients taking immunosuppressive drugs.
To understand this, let’s briefly review how COVID-19 vaccines stimulate the immune system to start building an immune response by making neutralizing antibodies against the spike protein, which is the first line of defense that protects us from natural infection. Data shows that this short-term neutralizing antibody response is quick and persists at clinically protective levels for at least eight months (eg, humoral immunity), while the longer-term protection is due to cellular immunity mediated by T cells.
Despite causing a surge in infections this summer that has resulted in thousands of hospitalizations and deaths among the unvaccinated, the Delta variant is not particularly good at evading the neutralizing antibodies generated by vaccination, according to a study by researchers at Washington University School of Medicine in St. Louis published recently in the journal Immunity. Thus, those fully vaccinated are well protected from serious disease, hospitalization and death for at least the first eight months or perhaps longer.
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