Moderna Inc. said on Sept. 3 the company had asked the EU drugs regulator for conditional approval of a booster shot of its Covid-19 vaccine at a 50 microgram dose.

Moderna Inc. on Sept. 1 asked the U.S. Food and Drug Administration to allow the use of a third booster dose of the company’s Covid-19 vaccine.

More studies into vaccinated populations show that although antibody responses drop months after vaccination against Covid-19, they still dramatically protect against severe disease and hospitalization. Studies are also continuing on the value and efficacy of booster shots, particularly against the Delta variant.

Sinopharm’s Covid-19 vaccine elicited weaker antibody responses against the Delta variant, based on the first published study of its effect against the more contagious version.

Data from a mid-stage clinical study of an experimental vaccine candidate developed by Affinivax and Astellas Pharma for Streptococcus pneumoniae shows ASP3772 is well tolerated and generated an antibody response against the deadly bacterial infection.

A third shot of the Oxford-AstraZeneca Covid-19 vaccine produces a strong immune response, researchers said on June 28, adding there was not yet evidence that such shots were needed, especially given shortages in some countries.

Pfizer’s Covid-19 vaccine generates antibody responses three-and-a-half times larger in older people when a second dose is delayed to 12 weeks after the first, a British study said.

The first study to directly compare immune reactions between Pfizer’s and AstraZeneca’s Covid-19 vaccines found strong and broadly similar antibody responses in over-80-year-olds after a first dose of either shot, scientists said on April 14.

Pfizer and BioNTech on March 31 announced data from a Phase III study which showed 100 percent efficacy and robust antibody responses in patients ages 12-15 years old who received the BNT162b2 vaccine.

Moderna believes the company’s Covid-19 vaccine protects against new variants found in Britain and South Africa, although it will test a new booster shot aimed at the South Africa variant after concluding that the antibody response could be diminished.