Vaccinated individuals

Several COVID-19 vaccines have now been shown to provide protection against COVID-19 and many more are still under development.92,93 There are still many unanswered questions regarding the longevity of immunity offered by vaccines, if they will be efficacious against all strains of COVID-19, which vaccines are most efficacious in different patient cohorts, and if vaccinated individuals are able to acquire and transmit COVID-19 without becoming infected. Studies are ongoing to answer all these questions using a range of testing strategies.
In order to assess the longevity of vaccine-mediated immunity, high-throughput quantitative anti-spike (S) antibody tests (as most vaccines currently elicit a response against the SARS-CoV-2 S- antigen) will be useful.94 Anti-nucleocapsid antibody tests may also be used to assess natural versus vaccine-mediated immunity.95-97 Many serological assays have been shown to correlate with neutralizing antibody titres;98,99however, direct assessment of neutralizing antibodies is preferable where possible as it is not fully understood how antibody test positivity relates to protective immunity against SARS-CoV-2.96,100 Assessments of cellular immunity are also necessary to completely understand how COVID-19 vaccines offer protection and how long this protection lasts.
In order to assess whether new variants are emerging that have the potential to escape vaccine-mediated immunity, full genome analysis is needed to better track evolution and spread of lineages, with particular focus on regular S gene sequence analysis and vaccinated sera challenge studies of emergent strains.101,102