The Centers for Disease Control and Prevention (CDC) has quietly updated its guidance on how late the second dose of a coronavirus vaccine can be administered after insisting it would not allow delays in shots.
Currently, the two vaccines approved by the U.S. Food and Drug Administration (FDA), one by Pfizer-BioNTech and the other by Moderna, are given three weeks and four weeks apart, respectively.
But in a new advisory posted to its website on Thursday, the CDC said the shots can be given up to six weeks apart.
‘The second dose should be administered as close to the recommended interval as possible,’ the CDC wrote.
‘However, if it is not feasible to adhere to the recommended interval, the second dose… may be scheduled for administration up to 6 weeks (42 days) after the first dose.’
It comes as several states report a shortage of shots, leading to concerns the the federal government is attempting to stretch the national vaccine supply.
So far, a total of 39.8 million doses have been distributed across the country but just 19.1 million have been administered.
Vaccines from Pfizer and Moderna are meant to be administered in two doses given three or four weeks apart, respectively, but the CDC updates its guidance, saying the second dose can be given up to six weeks after the initial dose. Pictured: A pharmacist prepares a syringe of the Pfizer-BioNTech COVID-19 vaccine Friday, January 9
The CDC warned Americans not to get one dose from Pfizer and the other from Moderna except in ‘exceptional situations.’ Pictured: Jackie Barry, a resident of The Open Hearth mens shelter, receives the Pfizer-BioNTech Covid-19 vaccine in Hartford, Connecticut, January 22
The CDC says it cannot recommend giving doses any later than six weeks because there is no enough data on doses administered after that time.
The agency says a person may only receive a second shot for different vaccine in ‘exceptional situations.’
‘These mRNA COVID-19 vaccines are not interchangeable with each other or with other COVID-19 vaccine products,’ the CDC wrote.
‘The safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the same product.
‘In exceptional situations in which the first-dose vaccine product cannot be determined or is no longer available, any available mRNA COVID-19 vaccine may be administered at a minimum interval of 28 days between doses.’
Delaying the administration of the second vaccine dose is a strategy that the UK implemented when it began its mass vaccination campaign
Health advisors in Britain said they were recommending a gap of up to 12 weeks between the two shots in an effort to provide more people with a first dose – and with some protection against COVID-19.
Dr Anthony Fauci, the nation’s top infectious disease expert, was he did not believe the U.S. should delay administering second doses like the UK
‘We know from the clinical trials that the optimal time is to give it on one day and for [the Moderna vaccine] wait 28 days and for Pfizer 21 days later,’ he told CNN.
Fauci said that one could ‘make the argument’ for stretching out the doses, he is not in favor of doing so.
A total of 39.8 million doses have been distributed but just 19.1 million have been administered
Pfizer and BioNTech also said here is no evidence to suggest its vaccine works if given more than 21 days after the first dose
‘Pfizer and BioNTech’s Phase 3 study for the COVID-19 vaccine was designed to evaluate the vaccine’s safety and efficacy following a 2-dose schedule, separated by 21 days,’ the companies said in a statement to CNBC.
‘There is no data to demonstrate that protection after the first dose is sustained after 21 days.’
There are also worried that delayed a dose gives more opportunity for virus to ‘learn’ how to defeat – or skirt around – protection given by the vaccines.
‘My concern, as a virologist, is that if you wanted to make a vaccine-resistant strain, what you would do is to build a cohort of partially immunized individuals in the teeth of a highly prevalent viral infection,’ Dr Paul Bieniasz, of Rockefeller University. told STAT News.
‘You are essentially maximizing the opportunity for the virus to learn about the human immune system. Learn about antibodies. Learn how to evade them.’