T cell immune responses seen a year after infection

A new study from Wuhan, evaluates the protective effect of memory T cell immune responses against severe disease 12 months after primary infection.

Key Findings:

• Independent of severity:
• It is found that neutralising antibodies were detectable even 12 months after infection in “most individuals”, and it remained stable 6-12 months after initial infection in people younger than 60 years.
• The researchers found that multifunctional T cell responses were detected for all SARS-CoV-2 viral proteins tested.
• Neutralising antibodies:
• SARS-CoV-2-specific neutralising antibody and T cell responses were retained 12 months after initial infection.
• Neutralising antibodies to the D614G, Beta, and Delta were reduced compared with those for the original strain, and were diminished in general.
• Memory T cell responses to the original strain were not disrupted by new variants.
• Robustness of T cells:
• The study reveals the durability and robustness of the T cell responses against variants, including Delta, even after one year of infection.
• Most importantly, the robust and longstanding T cell responses were seen in people who have not been reinfected or vaccinated.
• This would mean even in the absence of vaccination, a person who has been infected by the virus even one year ago would have robust immune responses, which would offer protection against disease progressing to a severe form requiring hospitalisation. 
• Lack of studies:
• No studies have been done to evaluate if booster doses improve T cell immune responses, which is the most important criterion of vaccination.
• Response to strains
• A year after infection, 82% individuals had neutralising antibodies against the original strain from Wuhan, China.
• In contrast, only 48% had neutralising antibodies against D614G,
• 23% had neutralising antibodies against the Beta variant, and
• 49% had neutralising antibody responses against the Delta variant.