There is substantial immunologic and increasing epidemiologic evidence that vaccination following infection further increases protection against subsequent illness among those who have been previously infected.
Laboratory studies indicate that hybrid immunity (i.e., immunity conferred by the combination of previous infection and vaccination) offers greater protection against COVID-19 infection.
A single dose of the AstraZeneca COVID-19 vaccine following SARS-CoV-2 infection induced a 2 to 3-fold increase in anti-Spike and -RBD IgG levels 30 days post-vaccination.
A study in Brazil found that hybrid immunity showed a modest increase in protection against symptomatic infection and waning over time.
Neutralising antibody titres against SARS-CoV-2 variants over 7 months following Pfizer vaccination in SARS-CoV-2-recovered and naïve healthcare workers resulted in substantially enhanced T-cell responses, anti-spike IgG responses and neutralising antibodies effective against SARS-CoV-2 variants in recovered participants.
Pfizer and Moderna vaccines were associated with greater IgG responses compared to Johnson & Johnson regardless of administration following infection.
Those with vaccine-after-infection or vaccine-breakthrough-infection had a more durable anti-spike-IgG response compared to infection-alone.
A study on healthcare workers from Oregon Health & Science University found enhanced immune responses after vaccination in COVID-19 recovered (hybrid immunity) compared with their naïve-vaccinated peers. However, the effects of post-vaccination breakthrough infections on humoral immune response remain to be determined.
Groot, G; Reeder, B; Muhajarine, N; Lee, S; Badea, A; Jagwani, M; Fox, L; Miller, L. What is known about hybrid immunity to COVID-19? 2022 Jun 06, Document no.: INF220501 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2022. 11 p. (CEST rapid review report).