The AstraZeneca COVID-19 vaccine, developed with the University of Oxford, has been authorized for use in more than 70 countries, with millions of jabs already administered across the UK, the European Union and around the world. 

But the U.S. hasn't authorized administration of the vaccine.

While AstraZeneca's vaccine has been a hot topic of discussion in recent weeks, due to the suspension of the jab in more than a dozen countries over blood clot concerns, both the European Medicines Agency (EMA) and the World Health Organization (WHO) have deemed it safe for use and said its benefits outweigh its risks. 

The UK was the first country in the world to begin its vaccination drive in early December with the Pfizer BioNtech jab and on December 30, 2020, AstraZeneca vaccine was also approved for use. It took the EMA another month to determine the vaccine was safe for use in the EU.

While several other countries have since authorized its use, the U.S. is one of those that has yet to do so, despite already having authorized three other vaccines including the Pfizer-BioNTech, Moderna and Johnson & Johnson jabs. This is mainly due to issues around AstraZeneca's clinical trials.

The U.S. approval process is ongoing

The U.S. Food and Drug Administration (FDA), the federal agency of the Department of Health and Human Services, has its own drug approval process, which is independent of other global agencies.

It requires data from human clinical trials in the U.S. to determine whether a vaccine is safe and effective, rather than accepting results from trials in other countries, before it can issue an authorization.

Concluding in March, AstraZeneca's large-scale trial showed the vaccine to be 79 percent effective at preventing symptomatic COVID-19 and was 100 percent effective in stopping severe disease and hospitalizations.

The figures exceed the FDA's threshold. 

To pass muster, the vaccine will need to prevent disease or decrease the severity of the disease in at least 50 percent of people vaccinated. Moderna, Pfizer-BioNTech and Johnson & Johnson have shown through U.S.-based trials that their vaccines are well above that and were therefore given emergency authorization by the FDA.

Drug approvals usually take months once an application is filed, but the FDA's emergency authorizations for COVID-19 vaccines have been granted within weeks, mainly thanks to the government's Operation Warp Speed, initiated last year by the then president Donald Trump to accelerate the testing, supply, development and distribution of safe and effective vaccines, therapeutics, and diagnostics to counter COVID-19.

AstraZeneca was awarded up to $1.2 billion through the operation. While Operation Warp Speed had previously estimated that AstraZeneca would file for authorization in January 2021, issues involving delays with the vaccine trials due to adverse reactions put this into question.

The U.S. trial was bigger than its previous trials in other countries, involving up to 32,000 volunteers – roughly the same number as the clinical trials conducted by Pfizer-BioNTech and Moderna. 

The FDA will now review the positive data and issue the authorization in about a month's time, Francis Collins, director of the National Institutes of Health, said in an interview.

Ahead of the results, AstraZeneca spokeswoman Michele Meixell said: "We expect data from our U.S. Phase III trial to be available soon, and we plan to file for emergency use authorization shortly thereafter."
 

Confusing initial trial data 

A challenge that faced AstraZeneca in gaining FDA approval was that its initial trial data had been slightly murky and confusing. 

Trial results pooled from differently designed clinical trials in the UK and Brazil – a break from standard practice in reporting the results of drug and vaccine trials – raised questions about dosing as well as how well it works for people over the age of 65.

Last year, in November, AstraZeneca reported that its shot was 62 percent effective at preventing COVID-19 among nearly 8,900 volunteers in Brazil and the UK. The participants in that trial received two full doses, but around 2,800 others accidentally received a half dose followed by a full dose a month later. Among that smaller group, the vaccine's effectiveness rose to 90 percent – which AstraZeneca then averaged, stating that the vaccine was 70 percent effective. 

Upcoming vaccine authorizations

While AstraZeneca waits with bated breath to finally receive U.S. authorization, other companies are also inching their way towards getting approval for their vaccines in the country.

U.S.-based Novavax, which received $1.6 billion through Operation Warp Speed in July, has ramped up full-scale manufacturing operations. Its spokesperson Silvia Taylor said the company has been in "ongoing contact" with the FDA and is "already beginning to submit" various parts of its application and data to agency officials. It expects initial results of its U.S. phase-three trial before summer.

Taylor said Novavax has already "locked" its manufacturing process at scale and will be ready to distribute in the U.S. as soon as emergency use is approved.

Canadian biotechnology company Medicago and its British partner GlaxoSmithKline have announced the start of phase-three clinical testing after receiving approval from U.S. regulatory authorities to proceed based on positive interim phase-two results.

Worldwide, 23 vaccines have currently reached the final stages of testing, with dozens more undergoing various other trials at different stages.