The federal regulators announced that they will now allow “mixing and matching” of all three authorised vaccines in the United States, which includes the Pfizer shot.
“Today’s actions demonstrate our commitment to public health in proactively fighting against the Covid-19 pandemic,” acting FDA Commissioner Dr Janet Woodcock said in a statement.
“As the pandemic continues to impact the country, science has shown that vaccination continues to be the safest and most effective way to prevent Covid-19, including the most serious consequences of the disease, such as hospitalisation and death.”
The FDA authorised the Johnson & Johnson booster for anyone 18 and over, while the Moderna booster, a half-dose of the original shot, was authorised for people 65 and older, or adults at risk of severe illness or complications because of underlying medical conditions or exposure on the job.
It means that the 15m Americans who originally got the single-shot Johnson & Johnson vaccine can now get a booster dose with Moderna or Pfizer-BioNTech, as long as they are 18 or older.
Around 70m Americans are fully vaccinated with Moderna, according to the Centers for Disease Control and Prevention.
Medical professionals could start giving the booster shots by the end of the week, once CDC advisers have met and a decision is made by a decision by its director, Rochelle Walensky.
Pfizer’s booster shot was authorised last month for elderly Americans, people with underlying medical conditions and those who live or work in high-risk settings.
A head-to-head comparison published by the CDC last month found that vaccine effectiveness against hospitalisation was 93 per cent for the Moderna vaccine, 88 per cent for Pfizer, and only 71 per cent for Johnson & Johnson.
Nearly 11m people have so far received a booster because they are immunocompromised.
Pfizer-BioNTech has also applied for emergency use authorisation for its vaccine to be given to children aged five to 11, with a decision expected by early next month.
The US has seen around 45.2m Covid-19 cases and more than 729,000 deaths during the pandemic.
As of 19 October a total of 189,487,793 Americans had been fully vaccinated, or 57.1 per cent of the country’s population, according to CDC data.
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