The video-sharing platform has taken the action after a video went viral claiming that the deadly respiratory virus is caused by 5G.
YouTube told the BBC: "We have clear policies that prohibit videos promoting medically unsubstantiated methods to prevent the coronavirus in place of seeking medical treatment, and we quickly remove videos violating these policies when flagged to us.
"Now any content that disputes the existence or transmission of Covid-19, as described by the WHO [World Health Organization] and local health authorities is in violation of YouTube policies.
"This includes conspiracy theories which claim that the symptoms are caused by 5G.
"For borderline content that could misinform users in harmful ways, we reduce recommendations.
"We'll continue to evaluate the impact of these videos on communities around the world."
YouTube's vow comes after UK mobile networks hit back at the absurd claims.
As a result, some masts were damaged by vandals.
Vodafone's chief executive, Nick Jeffery, said: "It beggars belief that some people should want to harm the very networks that are providing essential connectivity to the emergency services, the NHS, and rest of the country during this difficult lockdown period."
BT and EE tweeted: "Phone masts keep us all connected at this extraordinary time. And yet we're seeing reports of masts vandalised because of a conspiracy theory linking 5G tech to the spread of Covid-19.
"This claim is baseless. We must look after the infrastructure and people keeping us in touch."
And all of the UK's networks published a joint message, in which they revealed several of their engineers and key workers have also received abuse.
They wrote: "Our networks provide essential connectivity to our emergency services and the NHS; they enable families to check in on their isolated or vulnerable loved ones; parents to teach their children from home, and millions to be informed and entertained as they stay home.
"We are 100% focused on making sure the UK's mobile and broadband networks are resilient, ensuring you, your families and businesses, can keep connected when you need it most.
"Sadly, we have experienced cases of vandals setting fire to mobile masts, disrupting critical infrastructure and spreading false information suggesting a connection between 5G and the COVID-19 pandemic. There is no scientific evidence of any link between 5G and coronavirus. Fact.
"Stopping this is critical to keeping your communities connected.
"Not only are these claims baseless, they are harmful for the people and businesses that rely on the continuity of our services.
"They have also led to the abuse of our engineers and, in some cases, prevented essential network maintenance taking place.
"Please help us to make this stop.
"If you witness abuse of our key workers please report it. If you see misinformation, please call it out. Your help will make a real difference. Thank you for your support as we work together to keep our nation connected."