It important to note that antibodies are incomplete predictors of protection. After vaccination or infection, many mechanisms of immunity exist within an individual not only at the antibody level, but also at the level of cellular immunity.
14,
15,
16 It is known that SARS-CoV-2 infection induces specific and durable T-cell immunity, which has multiple SARS-CoV-2 spike protein targets (or epitopes) as well as other SARS-CoV-2 protein targets. The broad diversity of T-cell viral recognition serves to enhance protection to SARS-CoV-2 variants,
15 with recognition of at least the alpha (B.1.1.7), beta (B.1.351), and gamma (P.1) variants of SARS-CoV-2.
17Researchers have also found that people who recovered from SARS-CoV infection in 2002–03 continue to have memory T cells that are reactive to SARS-CoV proteins 17 years after that outbreak.
15 Additionally, a memory B-cell response to SARS-CoV-2 evolves between 1·3 and 6·2 months after infection, which is consistent with longer-term protection.
18
Some people who have recovered from COVID-19 might not benefit from COVID-19 vaccination.
6,
19 In fact, one study found that previous COVID-19 was associated with increased adverse events following vaccination with the Comirnaty BNT162b2 mRNA vaccine (Pfizer–BioNTech).
20 In addition, there are rare reports of serious adverse events following COVID-19 vaccination.
21 In Switzerland, residents who can prove they have recovered from a SARS-CoV-2 infection through a positive PCR or other test in the past 12 months are considered equally protected as those who have been fully vaccinated.
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