A new study reveals the two-dose COVID-19 vaccine developed by Pfizer and BioNTech is 90% effective at keeping someone from being hospitalized from the virus up to six months after receiving the second dose. Researchers from Pfizer and U.S.-based health care consortium Kaiser Permanente observed the records of about 3.4 million people who were members of Kaiser’s Southern California health insurer and provider program between December 2020 and August of this year. The study, published Monday in The Lancet medical journal, also revealed the vaccine was 93% effective against the highly contagious Delta variant for at least six months after the second shot. But the researchers also found that the vaccine’s effectiveness against infection dropped from 88% one month after completing the regimen to 47% after six months. The new study was published on the same day the European Union’s drug regulator approved the use of booster shots of the Pfizer-BioNTech COVID-19 vaccine for those aged 18 years and older, but left it to individual countries to decide whether or not to recommend the shots for widespread use. The European Medicines Agency said in a statement Monday that a booster dose of the Pfizer vaccine “may be considered at least 6 months after the second dose for people aged 18 years and older.” The agency said people with a severely weakened immune system should be given a third dose of the Pfizer or Moderna vaccine at least 28 days after they have received their second shot. The guidance comes as some EU member states have already begun administering booster shots, while others are still debating how broadly to use boosters in their populations. Meanwhile, the New York Times newspaper said Monday that Johnson & Johnson will ask the U.S. Food and Drug Administration to approve a booster shot of its single-dose COVID-19 vaccine. The U.S. drugmaker announced last month that clinical trials show a second shot of its vaccine increased its effectiveness against the virus to 94% about two months after the first dose, which provided about 70% effectiveness. Johnson & Johnson said the company is submitting the results of its studies to the FDA, the U.S. Centers for Disease Control and Prevention, the European Medicines Agency and other health authorities for potential use of the vaccine as a booster eight months or later after the primary single-dose vaccination. Johnson & Johnson’s request comes less than two weeks after the FDA authorized a third shot of the Pfizer-BioNTech two-dose COVID-19 vaccine for Americans 65 years old and above and adults at high risk of severe illness. The FDA is currently considering whether to approve a third shot of the two-dose Moderna vaccine. Some information for this report came from the Associated Press and Reuters.