Sunday, 26 June, 2022
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If I had Covid-19 am I immune? This is what scientists know so far

Based on research so far, it’s reasonable to assume that most people who’ve had Covid-19 are less likely to be re-infected, and less likely to get a severe case if they do.

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A mere month ago, the idea of immunity passports had raised hopes that people who survived Covid-19 would be freed from indefinite, costly confinement. Scientists warned, though, that our immune systems, while natural wonders, don’t always provide iron-clad protection against future viral attack. This virus was too new to know.

Now scientists have new evidence that our immune systems do retain various powerful defensive weapons after SARS-CoV2 is cleared. This is critical new information. Here’s a quick update on this and other recent developments in what we know about Covid-19 immunity:

Immunity Is More Than Just Antibodies

new paper in the journal Cell showed that people who’ve recovered from Covid-19 not only have antibodies, but retain immune system components known as T-cells, which, among other things, can clear the virus by killing infected cells.

The researchers compared 10 people who had been infected with 11 control subjects and determined that those who had fought off infections were armed with not only antibodies but also with CD4 cells, sometimes called a helper T-cells, which are important for getting a good antibody response. They also retained CD8 cells, or killer T-cells, which kill cells that are infected with the virus.

It’s reasonable to assume most people who’ve had Covid-19 are less likely to be re-infected, and less likely to get a severe case if they do, says Florian Krammer, a professor at the Icahn School of Medicine at Mount Sinai and co-author of the paper.

What they still don’t yet know, Krammer says, is whether the immune response is good enough to prevent people from picking up a second, milder infection and transmitting it. He’s involved in a long-term study following people who’ve had the disease for a year to see how often, if ever, they get re-infected.

The Cell study showed that about half of people who had never had Covid-19 carried T-cells left over from infections with other coronaviruses. (About 30% of common colds are caused by coronaviruses.) While some early news reports hinted that cold-induced T-cells might protect people from Covid-19, Krammer says they’re unlikely to play a big role. Everyone has had a cold-causing coronavirus in the past, and there’s little indication this is helping anyone avoid Covid-19.

Another study released this week in Science bolstered the evidence for post-infection immunity by attempting to deliberately infect monkeys twice. A week after the monkeys recovered from an initial infection induced by spraying particles of virus into their noses, the researchers again exposed the monkeys to this same “challenge.”  The monkeys resisted a second infection. That group, led by Harvard’s Dan Barouch, also performed a similar challenge study on monkeys that had not been previously infected but had been given an experimental vaccine based on DNA that holds the code for viral proteins needed to stimulate the immune system. Those monkeys, too, resisted getting infected. Those results were published in a second Science paper.


Also read: India ranks low on Covid testing but has done well on number of infections and deaths


This is Good News for Vaccine Developers

The findings on coronavirus immunity gives new reason for optimism that it will be possible to artificially induce an immune reaction with a vaccine.

The T-cell finding is the really big news here. The antibodies induced by a vaccine could wane fast if T-cells aren’t also sticking around. So the most promising vaccines will be those that induce both T-cells and antibodies to Covid-19, says University of Iowa biology professor Stanley Perlman, an expert on coronaviruses.

Immunity Shields Could Be the New Immunity Passport

The notion of immunity passports has fallen out of favor, as ethicists have started publishing long lists of reasons for disapproval. Now, some researchers are looking into “immunity shields” — a system in which people likely to be immune perform higher-risk jobs. This would shield non-immune workers from infection while allowing important services to resume.

If vaccines become available, they could be deployed strategically to strengthen these immunity shields. Early access to vaccines might go to people who work in grocery stores or factories, or to police officers or ambulance drivers. “That’s a very important discussion that hasn’t happened yet in this country,” says Krammer.

Commercially Available Antibody Tests Still Aren’t Good Enough to Bet Your Life On

Now for the bad news. Many people think that the cold or flu they had last winter might have been Covid-19, and are hoping they are immune. Already, local clinics are offering people antibody tests. But many of these tests aren’t accurate enough to indicate which individuals are safe from infection — especially if they weren’t tested for the virus when they had symptoms.

A new analysis in Science Immunology lays out this warning. In a region where about 5% of the population has had an infection, for example, if you took a test advertised as having 96% percent specificity and 90% sensitivity, a positive result would mean you had just a 54% chance of being a true positive and having immunity. That could lead to a deadly mistake.

“There’s a lot of hype surrounding serology testing, and bad tests have flooded the market,” says Krammer, who is credited with leading the development of the first antibody assessment that’s considered reliable enough to be useful. For now, people should assume their own immunity at their own risk.

Antibody Testing Is Getting Better — Watch This Space

Finally, as widespread antibody testing, also called serology testing, gets more accurate, it could help us fight the pandemic in other ways. A paper published last week in Science outlined a few: Scientists can conduct more thorough “serosurveys” over large samples to understand who is getting the disease and how it’s spreading; doctors can identify people eligible to donate their antibodies, which have been used to treat severe illness in others; and such tests can be used as part of a continuing investigation into how the immune system fights off the virus.

Some of the first such studies came under fire for failing to get a representative sample of residents. For example, a study of Bay Area residents last month concluded that between 2.5% and 4.5% of residents had been infected (thus implying a lower death rate). Some critics thought that range was too high. But other surveys have gotten even higher numbers — for example, another survey in New York City led to estimates that 20% of residents had been infected so far, a figure that was 14% across New York state.

Krammer said these surveys are improving — not just because the tests are better, but because the people doing them are using better sampling techniques. Such surveys are starting to show which regions and occupations are highest risk, and arms scientists with critical knowledge about how the disease spreads.-Bloomberg


Also read: Reproduction rate is the coronavirus number that is worth watching


 

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1 COMMENT

  1. So little is known about this new virus that it is still not possible to reach proper conclusions.

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