Vaccination programmes require two doses but an analysis of the immune response in those previously infected suggests only a single dose might be required.
The anticipated immune response from a COVID-19 vaccination is the induction of neutralising antibodies and production of specific memory B cells that are called upon in the event of re-exposure to the virus. A number of studies have demonstrated that even among those with a prior COVID-19 infection, vaccination induces a sufficient level of neutralising antibodies. However, far less attention has been paid to the immune response after a booster vaccination in terms of both the antibody response and the level of memory B cells produced. A team from the Institute for Immunology, University of Pennsylvania, Philadelphia, US has examined the immune response to vaccination among COVID-19-naïve patients and those who had recovered from an acute infection. The team were particularly interested in the level of circulating antibodies and antigen-specific memory B cells that developed over the course of the first and second vaccination dose with either BNT162b or Moderna, in both groups of patients.
The study recruited 44 healthy individuals (i.e., those without self-reported comorbidities), 33 of whom were COVID-19-naïve and 11 who had recovered from a previous infection. Among COVID-19 naïve patients, baseline levels of IgG antibodies to either the full-length spike protein or the spike receptor binding domain (RBD) were undetectable but increased significantly after the first and second vaccination doses. In contrast, among COVID-19 recovered patients, although baseline IgG levels were detectable and boosted by the first vaccine dose, antibody titre levels did not increase further after the booster vaccine dose. In fact, one week after the second dose, levels of the anti-RBD IgG were similar in both naïve and recovered patients. Similarly, spike-specific memory B cell increased after both vaccinations in the COVID-19 naive group and while boosted by the first vaccination, among recovered patients, levels did not increase further after the second vaccination.
The authors commented on how their study suggested that there was little to be gained from a second vaccine dose among those who had a prior infection, because a single dose provided a sufficient immune boost. Nevertheless, the authors recognised that the data were based on a small number of patients and because the COVID-19-recovered individuals were not hospitalised, the study results might not be generalisable to those with more severe disease. They concluded by calling for confirmation of their findings in larger studies.
Goel RR et al. Distinct antibody and memory B cell responses in SARS- CoV-2 naïve and recovered individuals following mRNA vaccination. Sci Immunol 2021