A preprint paper yesterday provided evidence that cellular immunity that develops after COVID-19 infection protects against worrisome SARS-CoV-2 variant viruses. This is a different type of immunity from most prior studies which have only looked at blood antibody (protein) immunity. These lymphocyte killer responses are particularly important immunity for viral infections.
Cellular immunity involves recognition of small peptide sequences in the spike protein of the virus. The T cells that recognize these sequencs can be activated to directly kill cells infected with virus. This can control the infection even in the absence of antibodies that neutralize the virus.
Clinically, it appears that cellular immunity is more important in protecting against COVID-19 because people without antibodies have survived SARS CoV-2 infection, but individuals with defective cellular immunity do not, even when given antibody against the virus.
Variants have changes in their gene sequence that lead to alterations in the structure of the spike protein. Antibodies can be defeated by a few small changes in protein sequence seen in variant viruses. Cellular immunity, because it recognizes multiple sites within a protein, is not as easily defeated.
When immune lymphocytes are activated by variant viruses, then new immunity can be generated and eventually neutralize the virus. New antibodies to the modified virus can also be generated.
If immunity after infection can provide this type of protection, it should also be seen after two doses of a vaccine against SARS-CoV-2. This provides real hope that the current vaccines should protect us against all forms of COVID-19 including the variant viruses in the U.K., South Africa, and Brazil that have raised concern.