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