U.S. May Stretch Out Covid-19 Vaccine Supply With Half-Doses

People waiting to get tested for covid-19 at a testing site in Miami, Florida
People waiting to get tested for covid-19 at a testing site in Miami, Florida
Photo: Chandan Khanna/AFP (Getty Images)

The U.S. federal government is scrambling to increase the limited supply of covid-19 vaccines. A new proposal suggests doling out half-doses of the Moderna vaccine to some people, but it’s not yet clear whether Moderna or health agencies like the Food and Drug Administration would be on board for the idea, nor whether the strategy is scientifically sound.


The idea was announced by Moncef Slaoui, the chief scientific advisor of the government’s Operation Warp Speed program, during an interview on the CBS program “Face the Nation” Sunday morning. According to Slaoui, the half-dose plan would be the best option to lengthen vaccine supply. Another, similar idea suggests giving people only the first dose of either Moderna or Pfizer’s vaccine, which were authorized on a two-dose schedule, with the shots given a month apart.

“We know that for the Moderna vaccine, giving half of the dose to people between the ages of 18 and 55, two doses, half the dose, which means exactly achieving the objective of immunizing double the number of people with the doses we have,” Slaoui said on Sunday.

Slaoui, an expert microbiologist and former head vaccine researcher at GlaxoSmithKline, is no doubt referring to a subset of data from early clinical trials of the Moderna vaccine. Some people between the ages of 18 and 55 were given two 50-milligram doses of the vaccine, as opposed to 100 milligrams—the currently authorized amount per dose. These people appeared to create a similar immune response to the coronavirus as those given the two 100-milligram doses. Some animal research has also suggested the same pattern.

While many outside experts haven’t dismissed the idea outright, there are concerns about the plan’s viability. For one, the data is very limited. Out of the over 15,000 volunteers who received the Moderna vaccine in clinical trials, only about 200 people received the smaller doses. That means the evidence showing that the vaccine is highly effective (around 95%) at preventing illness from covid-19 is almost entirely based on the 100-milligram dosage. While both groups did appear to have similar immune responses on paper, scientists are still unsure about how these responses translate to actually protecting people from disease.

Perhaps the biggest stumbling block to the plan is that it may not really solve our current problem. There is indeed a limited supply of vaccine doses available, but the doses we do have aren’t reaching people in the first place. Only around 4 million Americans are thought to have received the vaccine as of early January, well below the projections of 40 million doses said to be available by the end of last year. Both big cities and small towns are suffering delays in vaccinating as many people as possible, while doses have nearly expired in some cases. Equally worrying are the stories of many people—including health care workers—refusing to take the vaccine at all. As much as half the country has expressed hesitating to get vaccinated, according to recent surveys.


We may eventually overcome these hurdles, and there are already reports of eligible people being turned away from being vaccinated in some areas. So any plan to make more out of the doses we have will likely receive some serious consideration. Neither Moderna nor the FDA has responded to a request for comment from Gizmodo regarding the proposal.

Born and raised in NYC, Ed covers public health, disease, and weird animal science for Gizmodo. He has previously reported for the Atlantic, Vice, Pacific Standard, and Undark Magazine.


Rodgers Collarbone

What possibly could have been a worse time for vaccine distribution to begin than a Trump lame duck session? This sucks.