What happened 

Shares of Moderna (MRNA -2.90%) fell 9% on Tuesday as the biotech raced to determine if its coronavirus vaccine is effective against a highly contagious new strain of the virus. 

So what

Investors and the world at large cheered when a phase 3 clinical trial showed Moderna's vaccine candidate, mRNA-1273, to be 94% effective against COVID-19 and 100% effective at preventing severe forms of the disease. Moderna's share price went on to nearly double after the drugmaker released data from an interim analysis of the clinical trial in mid-November. 

A downwardly sloping stock chart.

Moderna's stock has pulled back sharply in recent days. Image source: Getty Images.

However, after reaching an all-time high of $178.50 on Dec. 1, Moderna has lost roughly 30% of its value. Investors are growing increasingly concerned about a new strain of the coronavirus that is rapidly spreading throughout the U.K., which has led government officials to impose new lockdown measures and more than 40 other nations to enact travel bans. 

Now what 

Health officials are optimistic that Moderna's vaccine will prove effective against the new virus strain, but it will take time before they can be more certain. Moderna is currently performing tests to confirm its vaccine's efficacy against the new variant of the virus, and it hopes to be able to provide more data in the coming weeks.