One Dose or Two?

There are two theories out there about how to vaccinate.  One says, look, we have data only on the protocols that were adopted in the trials.  The Pfizer and Moderna vaccines were administered in two doses, three to four weeks apart.  We know that works.  Don’t mess with it.  Stick to the protocol and make sure everyone getting these vaccines gets both doses in the proper time frame.

The other says, our goal should be to get basic protection for as many people as possible as quickly as possible, especially since ominous variants are spreading.  We are in a race, and when time matters as much as it does now you cut a few corners.  Since it looks like vaccine effectiveness is pretty strong two weeks after the first dose, make sure we get that dose out there and then go back, when there’s time and enough supply, to top it up later.

As often with dichotomous choices, the best course is neither.

We are after two related but different goals.  One is to minimize death and suffering, the other to reduce transmission as rapidly as possible.  Based on what we know, it is likely that a second dose of the two-dose vaccines (and maybe a third when variant-aware boosters become available) will increase protection, especially for those vulnerable to severe Covid.  On the other hand, getting first doses out the door at maximum speed will hasten the end of the pandemic while shrinking the reservoir from which mutant strains can emerge.  Two goals, not one.

Logically, with two goals and two choices, we would expect a mixed solution to be best.  (1) Identify the subset of the population who would most benefit from a second dose.  These will be the most susceptible to severe or long-haul symptoms, including the elderly, those with compromised immune systems, prior lung damage and other risk factors.  They should get two doses in line with the current protocol.  (2) For the rest of the population, prioritize the first dose.

There is room for adjustment.  The size of the priority protection group can be increased or decreased as we learn more about the incremental effect of a second dose and the role of different risk factors.  Perhaps some people who wouldn’t qualify for this group on the basis of their own health conditions might be folded in because their occupation or social circumstances either puts them at greater personal risk of severe symptoms or magnifies the consequence of otherwise modest declines in transmission potential that may result from getting both doses.

There is a lot of space for judgment, but the principle of a two-track strategy to pursue two different goals is the starting point.