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Comment by ac29 | Hacker News Reader

> Wait... This doesn't scare anybody?

Not really. mRNA starts to degrade within minutes of injection, and lasts maybe at most a few days in your body. It cant turn back into DNA, so once its gone, it can no longer have any effect on you.

> Why has this not been approved before?

Its a relatively new technology that took a lot of work and money to make a stable, effective vaccine with. Its also relatively expensive to manufacture.

> Would an mRNA vaccine be approved under less pressing circumstances...?

Yes, though these almost certainly were approved faster than other vaccines would be because of the pressing nature of things.

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> once its gone, it can no longer have any effect on you.

If this is true, then how does it provide protection against COVID19 for more than a few days?

The mRNA itself isn't doing the protection - it's training your immune system to do that for you (in a safe way).

So its effect on the immune system lasts even after it's gone. So if it were to cause any problems (in the immune system, for example), those could also persist after the mRNA is gone. So how exactly is this line of reasoning reassuring?

Mostly because that's also how all other vaccines work, going back 200 years. Its really only the mRNA part that's new.

> So its effect on the immune system lasts even after it's gone.

The general principle is the same as for most vaccines: make the body generate its own antibodies (and/or T cells) for the virus in question. So in that sense of course its effect is long term, just like when you get sick with some virus and your body develops antibodies for it - the virus itself is gone, but the effect on the immune system is long-lasting.

From an FT article:

> Conventional vaccines administer an inactivated virus, or proteins from that virus, into the body to trigger an immune response, which can prevent subsequent infection.

> In contrast, mRNA technology — originally developed as a cancer therapy — injects genetic instructions into the body that tell cells to make viral proteins that prime the immune system. Although mRNA vaccines had been under development for several years for viruses including influenza, cytomegalovirus, HIV, rabies and Zika, the arrival of Covid-19 turbocharged the process.

- https://www.ft.com/content/74e41528-80c3-4b0f-b343-be43d90f0...

The immune response also happens for all other types of vaccines. That part isn't so different with mRNA vaccines.

Everything you're exposed to in your environment impacts the immune system. That's one of the mistakes anti-vax people make about childhood vaccination. They're like "Oh no, my baby can't handle six different vaccines in one shot, that must be too many at once surely" but actually it's a baby and babies eat dirt - its immune system is already seeing all sorts of new nonsense that isn't supposed to be there every day and problems are very rare, vaccination isn't any more of a problem.

So yes, but no. And it's reassuring compared to say DNA tweaking which would permanently change the instructions in some cell lines in your body, or more extremely germ line DNA tweaking which would alter your cells and those of any subsequent offspring you have.

> Not really. mRNA starts to degrade within minutes of injection, and lasts maybe at most a few days in your body.

According to the data I've seen on kinetics (these vaccines have been in development since 20 years ago, so there's plenty of basic and animal test data) there's production of the antigen at the site of injection for approximately ten days. There's some systemic production in the liver for 2-4 days, but that's it.

The mRNA can last this long (normally, as you correctly say, it would get broken up in minutes) due to the lipid nanoparticles it is bound to, which are the "secret sauce" of this vaccine.

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