More evidence: Opponents to delays say there isn’t enough evidence to support the change, and that the longer dosing schedule hasn’t been rigorously tested.

• The large clinical trials by vaccine manufacturers Pfizer and Moderna tested the efficacy of their vaccines with gaps of three and four weeks between doses respectively.

Over the last several months, more evidence has come out showing that a single dose of several COVID-19 vaccines provides a significant amount of protection against the disease.

• A report published by the CDC last week found that a single dose of the Moderna or Pfizer vaccines was 80% effective under real-world conditions.

• A recent study from Sheffield and Oxford Universities found that the first dose of a Pfizer vaccine almost always generates a strong immune response, according to a report from Reuters. 

• On Twitter, Atul Gawande, a former medical adviser to President Joe Biden, suggested that the U.K.’s strategy of delaying second doses has prevented cases from surging, as they are currently in Europe and the U.S.

During a COVID-19 briefing on Monday, White House medical adviser Anthony Fauci said delaying second doses has some merit, but he’s skeptical about the efficacy of single doses. Without more solid data, he wants to stay the course.

• “Although we always continue to keep an open mind, we consider the route that we’re on now .. the best route,” he said during the briefing.

Round 2: A recent report from STAT highlights a number of scientists, public health officials and politicians from the left and the right who continue to support delaying second doses.

• “Britain is the best argument for a delayed second dose strategy,” Zeke Emanuel, a former health adviser to Biden and President Barack Obama told STAT’s Lev Facher. “They seem to have done it pretty successfully. Even with the B.117 variant … their numbers are pretty remarkable.”

In a recent Twitter thread, Gawande pointed to the increasing prevalence of new coronavirus variants, signs that people aren’t adhering to safety measures and the efficacy of single doses.

• “As cases and hospitalizations rise again, we can’t count on behavior alone reversing this course,” Gawande wrote on Twitter. “It’s time for the Biden admin to delay 2nd vax doses to 12 weeks. Getting as many people as possible a vax dose is now urgent.”

Céline Gounder, another doctor who previously advised Biden, wrote on Twitter that preliminary research suggesting that delaying second doses could slow down the evolution of more dangerous variants has changed her position as well. 

• “I’m moving to being on the fence about delaying 2nd doses of Pfizer/Moderna COVID vaccine when I was before very much against delaying 2nd doses,” she wrote.

The logistics: For weeks, the pharmacy chain Walgreens has been scheduling Pfizer shots four weeks apart — the same timing as Moderna’s vaccine — because it was easier to manage appointments, according to The New York Times.

• The company has switched to the recommended schedule after complaints from customers and the CDC.

Walgreens’ scheduling system automatically scheduled all second doses for four weeks after the initial shot. Chief Medical Officer Kevin Ban told the Times that it was easier to use the same schedule for all shots. 

• A CDC spokesperson told the Times that, as of March 28, about 7% of U.S. vaccine recipients had received their second shot late.

• “The U.S. doesn’t have an official delayed dosing strategy, but many Americans are experiencing it informally,” New York Times reporter Rebecca Robins tweeted.

Tingling Dai, a supply chain researcher at Johns Hopkins University, tweeted that he didn’t think it was a big deal to delay appointments by one week, adding that the logistics benefits probably outweigh the costs.

• “Based on my research … the slight delay (1) has significant scheduling/logistics benefits and (2) can help end the pandemic a bit earlier,” he tweeted.

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J&J overseeing Emergent plant after fumble

The fumble: Last week, The New York Times reported that a Maryland factory operated by contract manufacturer Emergent BioSolutions ruined a large batch of Johnson & Johnson’s COVID-19 vaccines. 

• Now, Johnson & Johnson will oversee production of vaccines at that plant, according to a report from Axios.  

The federal government has asked Emergent BioSolutions to stop making AstraZeneca’s vaccine, which hasn’t been approved in the U.S. yet, in the same facility to avoid future mix- ups, according to The New York Times.

• “This was a decision that [Health and Human Services] made with Johnson & Johnson and AstraZeneca in complete collaboration. … AstraZeneca also agreed that this was the right course,” White House COVID-19 adviser Andy Slavitt said during a press conference on Monday.

What happened: Last week, The New York Times and several other news outlets originally reported that workers accidentally combined ingredients from the Johnson & Johnson and AstraZeneca vaccines.

• Later, Emergent CEO Robert Kramer told CNBC that the ingredients weren’t mixed up, but there was a quality problem.

That explanation doesn’t seem to match up with the federal government’s decision to move production of the AstraZeneca vaccine.

• Johnson & Johnson only has three sites that can produce drug substance. But AstraZeneca has more than 10 sites for producing drug substance, which should make it easier to shuffle production.

• In a statement, AstraZeneca said it’s working with the U.S. government to find a new manufacturing site.