Why a booster shot is a must to fight newer Covid-19 variants

Drugmaker Moderna said Thursday that its coronavirus vaccine is 93 percent effective only six months after injection.

In a statement regarding ongoing clinical trials, CEO Stephane Bancel added: "The Delta variant is a significant new threat, so we must remain vigilant."

All three of the current Covid-19 vaccines on the market in the US are believed to offer protection from the more contagious Delta variant. In rare "breakthrough" cases, in which vaccinated people get the virus, symptoms are generally mild or non-existent.

READ MORE: Moderna's Covid-19 vaccine shows promise against Delta variant

Bancel said the company is working on a booster shot that he envisions being a single-shot vaccine that would be doled once a year and would protect against Covid-19 and the basic flu. 

Bancel says in clinical trials, the booster shots "demonstrate robust antibody responses to Covid-19 variants."

Meanwhile, the Food and Drug Administration (FDA) is working on granting full approval for the Pfizer vaccine by September. The Moderna and Johnson & Johnson vaccines are expected to get full approval sometime after that approval. 

READ MORE: What do we know about the efficacy of Chinese vaccines so far?

The three vaccines have been available on an emergency use authorization and the FDA is speeding up its timetable to grant full-use authorization.

The moves come as vaccine hesitancy in parts of the US, even vaccine hostility, is helping the spread of the Delta variant. But the White House is reporting that in areas where hospitalizations have been surging, vaccination rates are starting to tick up.

US rejected WHO's call for booster shot moratorium as 'false choice'

The US on Wednesday rebuffed a call from the World Health Organization (WHO) to impose a worldwide coronavirus booster shot moratorium, saying it presents "a false choice." 

WHO Director-General Tedros Ghebreyesus earlier in the day urged the halt until at least the end of September to boost global equity and allow at least 10 percent of the population in every country to be vaccinated. 

"To make that happen, we need everyone's cooperation, especially the handful of countries and companies that control the global supply of vaccines," he said during a webinar in Geneva. 

White House spokeswoman Jen Psaki said the Biden administration believes it can allot jabs for domestic booster shots should they be recommended by domestic health authorities while continuing its efforts to distribute vaccines worldwide. 

"We believe we can do both, and we don't need to make that choice," she said. "We will have enough supply to ensure that if the FDA decides that boosters are recommended for a portion of the population, to provide those as well." 

Psaki was referring to the Food and Drug Administration (FDA), which is currently reviewing Covid-19 vaccines to determine if it should update its guidance on the shots or grant full authorization.