The National Health Service in the U.K. is increasing the maximum interval between shots for recipients of the Pfizer (NYSE:PFE) and BioNTech (NSDQ:BNTX) vaccine to 12 weeks. In a letter to hospitals, NHS advised that patients scheduled to receive the second dose of the vaccine on Jan. 4 should receive it nine weeks later.
The developers of the vaccine intended for doses to be delivered 21 days apart. Pfizer and BioNTech, however, tested administering the second dose up to 42 days after the first vaccination. Roughly 80% of the Phase 3 trial participants received the second dose within 10 weeks after the first.
While none of the vaccine developers mentioned above have thoroughly tested the 12-week interval, NHS has concluded the decision will have the most significant impact on mortality.
Pfizer said in a statement that the “safety and efficacy of the vaccine has not been evaluated on different dosing schedules as the majority of trial participants received the second dose within the window specified in the study design.”
The company also concluded that regulators study the impact of such modified dosing schedules on immunity to maximize protection.
The British Medical Association (BMA) criticized the revised dosing schedule. In a statement, the group concluded that asking general practitioners to “rebook appointments of tens of thousands of elderly and vulnerable patients, due to get their second dose of the Covid-19 vaccination in a few days’ time, is unreasonable and totally unfair.”