This is a summary, written by members of the CITF Secretariat, of:

Holder KA, Ings DP, Harnum DOA, Russell RS, Grant MD. Moderate to severe SARS-CoV-2 infection primes vaccine-induced immunity more effectively than asymptomatic or mild infection. NPJ Vaccines. 2022 Oct 21;7(1):122. DOI: 10.1038/s41541-022-00546-1.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A paper published in NPJ Vaccines by CITF-funded researcher Dr. Michael Grant (Memorial University of Newfoundland) shows that, in a group of individuals who had been infected with SARS-CoV-2, the immune response induced by the subsequent rounds of vaccination was stronger when the COVID-19 symptoms were more severe. Nonetheless, the boost in responses induced by the second dose of vaccine waned rapidly to insignificant levels ~2.5 months post-vaccination.

The study supports the conclusion that hybrid immunity initially induced by vaccination following past recovery from SARS-CoV-2 infection is more robust than immunity induced by either infection or vaccination alone.

Key findings:

  • Following a first dose of COVID-19 vaccine and recovery from previous SARS-CoV-2 infection, the level of antibodies against both the spike (S) protein and its receptor binding domain (RBD) significantly increased in the entire study cohort compared with before vaccination. Similarly, the frequency of circulating T cells also significantly increased.
  • Immune responses post-vaccination were stronger in this group, when compared to a comparable group of individuals never infected with SARS-CoV-2.
  • 5 months following the second vaccine dose, vaccine-induced boosting of immune responses was marginal, with no significant increase in antibody levels or T-cell frequency compared with post-dose one. Increases in vaccine-induced responses were also only minor when compared the group of COVID-na├»ve individuals (those never infected with SARS-CoV-2).
  • Participants who experienced moderate or severe symptoms showed stronger antibody and cell-mediated responses after both their first and second dose than asymptomatic individuals or those with mild symptoms.

35 people with a confirmed-SARS-CoV-2 infection occurring between March 2020 and March 2021 were recruited into the study. Most participants enrolled following the first wave of SARS-CoV-2 infections attributed to the ancestral strain. Following recovery from COVID-19, researchers assessed antibody and cell responses against SARS-CoV-2 before vaccination and after first and second doses of vaccine. The severity of infection was determined based on self-reported symptoms.