> Is this the policy that originally said that telling people to wear a mask to protect yourself from COVID was a mistruth, and then saying wearing a mask provides no additional benefit was a mistruth.

It doesn't seem so. From https://blog.twitter.com/en_us/topics/company/2020/covid-19 , one of the examples of a tweet to remove is: “now that it’s summertime, you don’t need a mask anymore, so don’t wear your mask!”

I don't see a time where Twitter's policy said otherwise.

> Is this also the policy that said saying COVID vaccines increased the risk of mydiocarditis in young people was a mistruth, and yet its now known to be true?

As I understand the policy, not per se. There were three factors:

1. it must be an assertion of fact (not an opinion), expressed definitively, and intended to influence others’ behavior.

2. Is the claim demonstrably false or misleading?

3. Would belief in this information, as presented, lead to harm?

Someone writing that there's a very rare (as in 0.0022% chance) of mydiocarditis in young people, then that appears to be within policy. If someone says young people shouldn't get the vaccine because of the increased chance of mydiocarditis, then that that likely falls under #1.

My "0.0022% chance" comes from Myocarditis or Pericarditis Following the COVID-19 Vaccination in Adolescents: A Systematic Review, M Li, X Wang, J Feng, Z Feng, W Li, B Ya - Vaccines, 2022

] Conclusions: Our study showed that myocarditis/pericarditis occurred after vaccination with the BNT162b2 or Comirnaty vaccine, especially after the second vaccination in male adolescents, but the incidence of myocarditis/pericarditis after vaccination with the above vaccines was very rare (0.0022%). Therefore, it is recommended that adolescents should be vaccinated with the COVID-19 universal vaccine as soon as possible and closely monitored for subsequent adverse reactions, which can be treated promptly.

also, quoting Evaluating the relationship between myocarditis and mRNA vaccination, Charlotte Switzer & Mark Loeb (2022) - Expert Review of Vaccines, 21:1, 83-89,

] Myocarditis may be associated with vaccination, through several biological mechanisms. Studies have shown that live viral vaccinations can act as a trigger for hypersensitivity inflammatory reactions, but further work is required to examine how the mRNA formulation may induce these autoimmune responses. Given that the risk of these adverse events is low, and the benefit of protection against disease is so great, the receipt of mRNA vaccines is recommended. ...

] Consistently, all patients hospitalized with mRNA-associated myocarditis have been discharged in stable condition and responded well to clinical management, resolving the episode [15–27].

> All it did was fuel conspiracy and discredit government advice.

Some of the other things covered on the policy were:

“5G causes coronavirus — go destroy the cell towers in your neighborhood!".

"Tweets offering the sale or facilitation of non-prescription treatments/cures for COVID-19, or those which advertise cures or treatments for COVID-19 that require a prescription or physician consultation."

"Specific and unverified claims made by people impersonating a government or health official or organization such as a parody account of official public health advisors claiming that hydroxychloroquine will prevent COVID-19."

"Claims that specific groups or nationalities are never susceptible to COVID-19, such as “people with dark skin are immune to COVID-19 due to melanin production” or are more susceptible, such as “avoid businesses owned by Chinese people as they are more likely to have COVID-19.”"

“Coronavirus is vulnerable to UV radiation - walking outside in bright sunlight will prevent COVID-19.”

“drinking bleach and ingesting colloidal silver will cure COVID-19.”

“COVID-19 does not infect children because we haven’t seen any cases of children being sick.”

“If you can hold your breath for 10 seconds, you don’t have coronavirus.”