Question: There’s been a lot of discussion and perhaps pressure to extend the vaccination period between doses or even lessen the doses for optimal coverage. Did the 2-dose vaccine producers release any data about the effectiveness of their vaccines after a single dose?  Would extending the period between doses or minimizing the second dose result in the drugs becoming less effective as the virus mutates, similar to our history with antibiotics or antimalarials?

Answer: We need to make evidence-informed, transparent decisions for best health outcomes and to bolster public trust.  Moderna’s and Pfizer’s clinical trial results were based on a two dose regimen spaced 28 days/21 days, respectively.  As Dr. Fauci told NBC last week, “If you want to stick with the data, that’s the way you should do it.”  On this matter, my thoughts align with the FDA’s stance described in the FDA press release of 1/4– “We know that some of these discussions about changing the dosing schedule or dose are based on a belief that changing the dose or dosing schedule can help get more vaccine to the public faster. However, making such changes that are not supported by adequate scientific evidence may ultimately be counterproductive to public health.”  

Just today, The BMJ published a fantastic article that gives detailed answers to your questions, Covid-19 vaccination: What’s the evidence for extending the dosing interval?  The article quotes Paul Bieniasz, a retrovirologist from Rockefeller University who stated, “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.”  It also provides a synthesis of the limited evidence on effectiveness of just one dose, reminding the reader that “Pfizer has said that it has no evidence that the protection [afforded by one dose] lasts beyond the 21 days.”

Finally, in the US our current problem isn’t a lack of vaccines; it’s overstretched local administration efforts. That’s the problem we need to be dealing with right now–  we need more resources and support for local public health efforts to address vaccine hesitancy and get the vaccine administered (Health Force!). Read on for a few more details in response to your questions.  

A bit more background: Last week, the UK announced a plan to delay the second dose of the Pfizer and AstraZeneka vaccines in order to get 1st doses out to more people.  With limited vaccination supply and the virus surging, the UK’s rationale is that “Prioritising the first doses of vaccine for as many people as possible on the priority list will protect the greatest number of at-risk people overall in the shortest possible time…”  The US is *not* following this approach.  However, recognizing that the US has not yet been able to procure enough vaccines for the entire population, NIH and Moderna scientists have begun analyzing the data to see if they can double the supply of the Moderna vaccine by halving doses.  Study results are expected in 2 months, and even if they are promising, they will still need to be reviewed and approved by the FDA, as reported yesterday in the NY Times.  Meanwhile, as also reported by the NY Times, “Officials are rushing to find supplies of more efficient syringes that could extract an additional dose from vials of the Pfizer-BioNTech vaccine and bolster the Pfizer supply by 20 percent.”