vial of Moderna vaccine

The US Food and Drug Administration will meet this week to consider giving half-doses of Moderna’s COVID-19 vaccine to people aged 18 to 55.

The move could make the vaccine available to twice as many people in this age group, according to Moncef Slaoui, chief scientific adviser of Operation Warp Speed, the US government's vaccine program.

Slaoui told CNN Chief Medical Correspondent Dr. Sanjay Gupta that the decision to cut the current 100-microgram dose in half, with another half-dose 28 days later, ultimately rests in the hands of the FDA.

Earlier data showed that binding and neutralizing antibody responses were similar among participants under 55 who received either 100-microgram or 50-microgram doses, Slaoui said. While an FDA briefing document last month also references these “comparable” immune responses from Moderna’s phase 2 study, the full data have not yet been published.

Slaoui said he’s “not sure it holds for Pfizer,” whose dose contains 30 micrograms. But that’s a conversation that has yet to happen, he added.

CNN has reached out to Moderna and Pfizer for comment. The US government previously secured 200 million doses each of Moderna’s and Pfizer’s vaccines.

US CDC hopes to double the number of coronavirus samples checked for new mutations

he US Centers for Disease Control and Prevention hopes to more than double the number of coronavirus genomes sequenced to watch for new mutations in the US over the next two weeks, a top official said Sunday.

The United States is now sequencing about 3,000 samples a week and the CDC hopes to more than double that to about 6,500 per week, according to Dr. Gregory Armstrong, director of the Office of Advanced Molecular Detection at the CDC's National Center for Emerging and Zoonotic Infectious Diseases.

Scientists sequence the genome -- the entire genetic map of the virus -- to find mutations that could affect how the virus spreads.

British scientists found a new variant of the virus was spreading there and say the pattern of mutations makes it more easily transmitted, although it does not appear to cause more severe disease.

It's now been found in at least 37 countries, including in the US, where cases have been identified in California, Colorado and Florida.

"It's important that we monitor the virus and that we be able to pick up these trends that have implications for public health and clinical medicine," Armstrong told CNN.

Data on whether COVID-19 variant first seen in UK is resistant to vaccine expected this week

Test results are expected this week from labs that are studying whether a variant of the coronavirus first identified in Britain might pose a challenge to COVID-19 vaccines, according to a World Health Organization official.

Scientists in the UK and elsewhere have taken blood from people who have been vaccinated. They are testing those samples to see if the antibodies created by the vaccine protect against the new strain, according to Maria Van Kerkhove, the WHO’s technical lead for coronavirus response.

They’re also taking blood from people who have been infected with the new variant to see how well the vaccine works against it, Van Kerkhove said.

Pfizer and Moderna, the makers of the two vaccines authorized in the US, are working to see if the vaccine is effective against different variants of the virus.

On Wednesday, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the immune response from the vaccines was “very likely” to protect against the new variant.

The UK variant has 17 mutations, an unusually high number.

Scientists are also doing tests to assess the vaccine’s efficacy against a variant found in South Africa that has 22 mutations, Van Kerkhove said.