Now we see evidence of what we have been observing in people for months, now: longterm immunity to SARS-CoV-2. With studies showing pre-existing immunity from other cold viruses (who shared such similar antigens with SARS-CoV-2 that it provided somewhere between 40%-60% immunity to the population), new studies are confirming that we see long term immunity even after exposure to SARS-CoV-2.
This is good news. And it reflects what we are seeing in places like Belgium, Sweden, and NYC: very near heard immunity as very few new cases and deaths are seen in those places.
Antibodies also come with an expiration date: Because they are inanimate proteins and not living cells, they can’t replenish themselves, and so disappear from the blood just weeks or months after they are produced. Hoards of antibodies appear shortly after a virus has breached the body’s barriers, then wane as the threat dissipates. Most of the B cells that produce these early antibodies die off as well.But even when not under siege, the body retains a battalion of longer-lived B cells that can churn out virus-fighting antibodies en masse, should they prove useful again. Some patrol the bloodstream, waiting to be triggered anew; others retreat into the bone marrow, generating small amounts of antibodies that are detectable years, sometimes decades, after an infection is over. Several studies, including those led by Bhattacharya and Pepper, have found antibodies capable of incapacitating the coronavirus lingering at low levels in the blood months after people have recovered from COVID-19.
“The antibodies decline, but they settle in what looks like a stable nadir,” which is observable about three months after symptoms start, Bhattacharya said. “The response looks perfectly durable.”
Seeing antibodies this long after infection is a strong indication that B cells are still chugging away in the bone marrow, Pepper said. She and her team were also able to pluck B cells that recognize the coronavirus from the blood of people who have recovered from mild cases of COVID-19 and grow them in the lab.
Multiple studies, including one published Friday in the journal Cell, have also managed to isolate coronavirus-attacking T cells from the blood of recovered individuals — long after symptoms have disappeared. When provoked with bits of the coronavirus in the lab, these T cells pumped out virus-fighting signals, and cloned themselves into fresh armies ready to confront a familiar foe. Some reports have noted that analyses of T cells could give researchers a glimpse into the immune response to the coronavirus, even in patients whose antibody levels have declined to a point where they are difficult to detect.
“This is very promising,” said Smita Iyer, an immunologist at the University of California, Davis, who is studying immune responses to the coronavirus in rhesus macaques but was not involved in the new studies. “This calls for some optimism about herd immunity, and potentially a vaccine.”
Notably, several of the new studies are finding these powerful responses in people who did not develop severe cases of COVID-19, Iyer added. Some researchers have worried that infections that take a smaller toll on the body are less memorable to the immune system’s studious cells, which may prefer to invest their resources in more serious assaults. In some cases, the body could even jettison the viruses so quickly that it fails to catalog them. “This paper suggests this is not true,” Iyer said. “You can still get durable immunity without suffering the consequences of infection.”
The researchers are also apt to point out that they do not have the smoking gun research that shows long-term immunity remains in place because it has still only been a few months after the first infections. But since the time tables are now exceeding the original 3 month antibody drop, and they are finding markers of anitbodies this long after, it speaks volumes to long-term immunity. As always, this is not a 100% across the board thing: others may become reinfected especially if they have poor immune systems.
https://www.chicagotribune.com/coronavirus/ct-nw-nyt-covid-immunity-mild-infections-20200817-hvv4tiiu5feklclx47bc74el34-story.html?outputType=amp