Immunity

Immunity & Herd Immunity

Since our bodies had to deal and were already in contact with different variants of coronaviruses in the past, it appears that most people already have a congenital, general or cross-immunity to e.g. influenza and other viruses.

Immunity to COVID-19 is probably higher than tests have shown
https://news.ki.se/immunity-to-covid-19-is-probably-higher-than-tests-have-shown

SARS-CoV-2 T-cell epitopes define heterologous and COVID-19-induced T-cell recognition
New German study confirms that 81% of pre-Covid blood donors show T-cell reaction against SARS-CoV-2. This Confirms that ~19% of people are only expected to be infected with Covid19!

SARS-CoV-2-specific peptides enabled detection of post-infectious T cell immunity, even in seronegative convalescent individuals. Cross-reactive SARS-CoV-2 peptides revealed pre-existing T cell responses in 81% of unexposed individuals and validated similarity with common cold coronaviruses, providing a functional basis for heterologous immunity in SARS-CoV-2 infection.

Published: 30 September 2020
https://www.nature.com/articles/s41590-020-00808-x

Targets of T Cell Responses to SARS-CoV-2 Coronavirus in Humans with COVID-19 Disease and Unexposed Individuals
Importantly, we detected SARS-CoV-2-reactive CD4+ T cells in ∼40%–60% of unexposed individuals, suggesting cross-reactive T cell recognition between circulating “common cold” coronaviruses and SARS-CoV-2.
https://www.cell.com/cell/fulltext/S0092-8674(20)30610-3

Diagnosis and Tracking of Past SARS-CoV-2 Infection in a Large Study of Vo’, Italy Through T-Cell Receptor Sequencing

We analyzed T-cell and antibody signatures in a large population study of over 2,200 individuals from the municipality of Vo’, Italy, including 70 PCR-confirmed SARS-CoV-2 cases (24 asymptomatic, 37 symptomatic, 9 hospitalized). Blood samples taken 60 days after PCR diagnosis demonstrated 97% (68/70) of the latter subjects had a positive T-cell test result, higher than an antibody serology assay (77%; 54/70 of subjects) performed on the same samples.
https://www.medrxiv.org/content/10.1101/2020.11.09.20228023v1

WHO changed the definition of herd immunity.
2019 definition and 2020 definition.