The stock markets fell on Friday after two pharmaceutical companies said their vaccines were slightly less effective against the South African strain of COVID-19.
The Dow Jones Industrial Average fell 620 points, or 2 percent, and the S&P 500 fell 73 points, or 1.9 percent, closing the worst week for Wall Street since October.
Johnson & Johnson announced Friday morning that its single-dose vaccine was 66 percent effective, but less effective against the South African strain.
But it proved to be 100% effective in preventing hospitalization or death after a month.
Thursday night, Novavax released similar results for his vaccine, which he said was 90 percent effective against COVID-19, but only 60 percent effective against the South African strain in people without HIV.
The advent of two new effective vaccines could vastly accelerate the vaccination campaign, but the less effective warning against the South African strain is raising concerns about a protracted fight against COVID-19.
The declines ended a tumultuous week of trading that was also shaken by retail traders betting on some stocks, such as GameStop, raising their ratings and taking down some traditional investors and hedge funds.
Updated at 4:09 points.