Could pre-existing and acquired immunity be the best protection against covid, helping solve the pandemic before vaccines are widely available?
Excellent summary of the latest immunology findings on sars-cov2 at the British Journal of Medicine [Mentioning the work of Portuguese researcher Gabriela Gomes].
Key points:
“… This would be because… of the result of a combination of pre-existing and newly formed immune responses, could now exist in the population, preventing an epidemic rise in new infections.”
“Could pre-existing immunity be more protective than future vaccines? Without studying the question, we won’t know.”
Highlights:
“It seemed a truth universally acknowledged that the human population had no pre-existing immunity to SARS-CoV-2, but is that actually the case? Peter Doshi explores the emerging research on immunological responses…
At least six studies have reported T cell reactivity against SARS-CoV-2 in 20% to 50% of people with no known exposure to the virus.”
“Maybe we were a little naive to take measurements such as serology testing to look at how many people were infected with the virus,” the Karolinska Institute immunologist Marcus Buggert told The BMJ. “Maybe there is more immunity out there.”
“… The research offers a powerful reminder that very little in immunology is cut and dried. Physiological responses may have fewer sharp distinctions than in the popular imagination: exposure does not necessarily lead to infection, infection does not necessarily lead to disease, and disease does not necessarily produce detectable antibodies. And within the body, the roles of various immune system components are complex and interconnected. B cells produce antibodies, but B cells are regulated by T cells, and while T cells and antibodies both respond to viruses in the body, T cells do so on infected cells, whereas antibodies help prevent cells from being infected.”
“T cell studies have received scant media attention, in contrast to research on antibodies, which seem to dominate the news (probably, says Buggert, because antibodies are easier, faster, and cheaper to study than T cells)…
But T cell studies allow for a substantially different, more optimistic, interpretation. In the Singapore study, for example, SARS-CoV-1 reactive T cells were found in SARS patients 17 years after infection…”
“T cell studies may also help shed light on other mysteries of covid-19, such as why children have been surprisingly spared the brunt of the pandemic, why it affects people differently, and the high rate of asymptomatic infections in children and young adults.”
“… This would be because… of the result of a combination of pre-existing and newly formed immune responses, could now exist in the population, preventing an epidemic rise in new infections.”
“But they were all quick to note that this is speculation. Formally, the clinical implications of the pre-existing T cell reactivity remain an open question. “People say you don’t have proof, and they’re right,” says Buggert, adding that the historical blood donor specimens in his study were all anonymised, precluding longitudinal follow-up…
“Right now, I think everything is a possibility; we just don’t know. The reason we’re optimistic is we have seen with other viruses where [the T cell response] actually helps you.” One example is swine flu, where research has shown that people with pre-existing reactive T cells had clinically milder disease.”
“Could pre-existing immunity be more protective than future vaccines? Without studying the question, we won’t know.”
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“Gabriela Gomes, an infectious disease modeller at the University of Strathclyde, is reviving concerns that the theory’s basic assumptions do not hold. Not only do people not mix randomly, infections (and subsequent immunity) do not happen randomly either, her team says. “More susceptible and more connected individuals have a higher propensity to be infected and thus are likely to become immune earlier. Due to this selective immunization by natural infection, heterogeneous populations require less infections to cross their herd immunity threshold,” they wrote. While most experts have taken the R0 for SARS-CoV-2 (generally estimated to be between 2 and 3) and concluded that at least 50% of people need to be immune before herd immunity is reached, Gomes and colleagues calculate the threshold at 10% to 20%…
Sunetra Gupta at the University of Oxford has arrived at similar conclusions of lower herd immunity thresholds…”