Americans can choose a Covid-19 booster shot that is different from their original inoculation but the recommendation is to stick with the vaccine they got first if available, White House chief medical adviser Dr. Anthony Fauci said on Oct. 22.

The U.S. government said on Aug. 18 it plans to make Covid-19 vaccine booster shots widely available starting on Sept. 20 as infections rise from the coronavirus Delta variant, citing data indicating diminishing protection from the vaccines over time.

Swiftly rising coronavirus cases across the United States and abroad fueled fears of a pandemic resurgence on July 19 and sent shockwaves through stock markets as the highly contagious Delta variant appeared to be taking hold.

Tokyo reported the highest number of new Covid-19 cases in almost six months on July 14, with the Olympics due to open in the capital in just nine days.

Pfizer and partner BioNTech plan to ask U.S. and European regulators within weeks to authorize a booster dose of the companies’ Covid-19 vaccine, based on evidence of greater risk of infection six months after inoculation and the spread of the highly contagious Delta variant.

The United States on June 14 crossed the grim milestone of 600,000 Covid-19 deaths, according to a Reuters tally, as slowing vaccination rates threaten the Biden administration target of having 70 percent of U.S. adults receive at least one shot and 160 million fully inoculated by July 4.

The European Union on May 6 backed a U.S. proposal to discuss waiving patent protections for Covid-19 vaccines, but drugmakers and some other governments opposed the idea, saying it would not solve global inoculation shortages.

India’s daily Covid-19 shots fell sharply from an all-time high reached in early April as domestic companies struggle to boost supplies and imports are limited, even as the country fights the world’s worst surge in infections. Pfizer said on May 3 the company was in discussions with the Indian government seeking an “expedited approval pathway” for its vaccine.

Moderna Inc. said on April 29 the company is boosting manufacturing capacity for its Covid-19 vaccine and expects to make up to 3 billion doses in 2022, more than twice the previous forecast.

There is a much higher risk of brain blood clots from Covid-19 infection than there is from vaccines against the disease, British researchers said on April 15, after the rollout of inoculations was disrupted by reports of rare clots.