Robert M. Wachter is chair of the department of medicine at the University of California at San Francisco. Ashish K. Jha is dean of the Brown University School of Public Health.

Until recently, we supported the strict vaccine regimen, requiring two doses within a month. Both the Pfizer and Moderna clinical trials were carried out this way, and the much-touted 95 percent efficacy rates were drawn from those trials.

But as Mike Tyson famously said, “Everybody has a plan until they’ve been punched in the mouth.” When it comes to covid-19, we’re being punched in the mouth over and over again. It’s time to change the plan; namely, we should give people a single vaccination now and defer their second shot until more doses of vaccine become available.

What changed? First, there’s simply a supply constraint. We hoped that additional vaccines would be available by now. But only the Pfizer and Moderna vaccines have been authorized, and they’re being produced more slowly than hoped. Even more worrisome are the distribution bottlenecks that are making it difficult to vaccinate people as quickly as possible.

As of Jan. 1, the United States has given first vaccine doses to about 1 percent of our population. Contrast this with Israel, which has vaccinated 10 percent of its population, including more than 40 percent of people older than 60. The benefits of the immunity these shots produce accrue not just to those getting vaccinated, but to broader society as well by slowing the virus’s spread. Until a lot more people are vaccinated, this latter benefit will be minimal.

Another factor is the state of the pandemic: Hundreds of thousands of people are being infected and thousands are dying every day. Any high-risk person who isn’t vaccinated today could be infected tomorrow and die in a month. But we are holding back half of the doses in reserve for people to get their second shots. That slows things down.

Now comes another punch to the mouth: the new variant of the coronavirus, which is likely much more contagious and is spreading rapidly in multiple U.S. communities. Epidemiological models and Britain’s experience indicate that, while only a few cases of the variant have been identified in the United States, it will likely become our dominant strain within a few months. Although the new variant doesn’t seem deadlier at the individual level, a more infectious virus means more cases, which means more hospitalizations and deaths. We need to vaccinate as many people as quickly as possible to save the most lives.

Whether the bottleneck is due to vaccine production or distribution, giving people a single shot now and waiting on the second until the shortage abates will get more people vaccinated sooner. But will it work? Here, the clinical trial results for the Pfizer and Moderna vaccines are reassuring. While they were designed to test the effectiveness of two shots given about a month apart, both showed that the first shot had a substantial benefit beginning around 10 days afterward. In both trials, by the time of the second shot, the first was already 80 to 90 percent effective in preventing covid-19 cases.

Across the United States, limited funding has undermined end-of-year efforts to hire coronavirus vaccine staff, create vaccination centers and raise awareness. (Reuters)

We are not arguing against people receiving two shots. The second shot adds a measure of effectiveness and likely makes vaccination-derived immunity more durable. That’s why we’re advocating that it be delayed, not dropped altogether. And an argument can be made that for groups at highest risk for exposure (such as health-care workers) and for death (such as Americans over age 75), sticking with the early second-shot strategy is reasonable. But for everyone else, the deferral strategy makes sense.

Is there any potential downside to a delay? Yes. The strategy hasn’t been studied, so we don’t know if and when the immunity from the first shot begins to wane. But data from Moderna, for example, is reassuring. It shows robust immune response four weeks after the first shot, and most experts believe it is extremely unlikely immunity would somehow plummet by week eight or even week 12 following a single shot. Another concern is that with a delay, some people may forget to get their second shot. It will require effort to track people and remind them to receive it.

A more general risk is that this would be yet another change in our pandemic strategy at a time when people have grown weary of our ever-changing response regarding opening schools, touching surfaces and wearing masks. If this change causes them to become exasperated and choose not to be vaccinated at all, that would be a problem. But we believe the advantages of rapidly vaccinating twice as many people would outweigh these potential disadvantages.

In a perfect world, there would be no trade-offs. But if 2020 taught us anything, it’s that we don’t live in a perfect world. Between 50,000 and 100,000 Americans will die of covid-19 this month alone. Giving 100 million people — particularly those at high risk — a single shot that is 80 to 90 percent effective will save far more lives than giving 50 million people two shots that are 95 percent effective. It’s what we should do.

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