A third dose of both the AstraZeneca and Pfizer-BioNTech COVID-19 vaccines significantly increased the immune response to the omicron variant, according to a new study by University of Oxford researchers. The laboratory study, which hasn’t been peer reviewed yet, compared antibody levels in blood samples from people who received two doses of vaccine with samples from those who had received a third dose. While two doses provided much less protection against omicron than earlier variants, levels of neutralizing antibodies rose sharply after a third dose, the study found. Also read: Boosters key to fight omicron, lot still to learn “In summary, neutralization titres against omicron are boosted following a third vaccine dose, meaning that the campaign to deploy booster vaccines should add considerable protection against omicron infection,” the researchers wrote. The study also found that unvaccinated people who had recovered from COVID-19 probably have “little protection from reinfection with omicron,” though they may have some protection against serious illness. Also read: Moderna: Initial booster data shows good results on omicron

The new omicron variant took only a few weeks to live up to dire predictions about how hugely contagious it is but scientists don’t yet know if it causes more severe disease even as the world faces exploding cases just before Christmas. “Everything is riskier now because omicron is so much more contagious,” said Dr. S. Wesley Long, who directs the testing lab at Houston Methodist Hospital — and over the past week has canceled numerous plans to avoid exposure. Omicron now is the dominant variant in the U.S., federal health officials said Monday, accounting for about three-quarters of new infections last week. The speed that it's outpacing the also very contagious delta variant is astonishing public health officials. In three weeks, omicron now makes up 80% of new symptomatic cases diagnosed by Houston Methodist’s testing sites. It took the delta variant three months to reach that level, Long said. Also read: Moderna: Initial booster data shows good results on omicron The mutant's ability to spread faster and evade immunity came at a bad time — right as travel increased and many people let down their guard. But what the omicron wave will mean for the world is still unclear because so many questions remain unanswered. Here’s the latest on what’s known and what’s still to learn about omicron. HOW MUCH PROTECTION DO VACCINES OFFER? Vaccines in the U.S. and around the world do not offer as much protection against omicron as they have against previous versions of the coronavirus. However, vaccines still help — a lot. Lab tests show while two doses may not be strong enough to prevent infection, a booster shot of either the Pfizer or Moderna vaccine produces virus-fighting antibodies capable of tackling omicron. Antibody levels naturally drop over time, and a booster revved them back up again, by 25 times for Pfizer’s extra shot and 37 times for Moderna’s. No one knows exactly what level is high enough — or how long it will be before antibody levels begin dropping again. After a booster, the protection against an omicron infection still appears about 20% less than protection against the delta variant, said Dr. Egon Ozer of Northwestern University. But if the virus gets past that first line of defense, the vaccinated have additional layers of protection. “The vaccines are going to protect you against severe disease, hospitalization and death,” said Houston Methodist's Long. “And that’s really the most important thing.” Those extra defenses include T cells that mobilize to beat back the virus, plus memory cells that, once reactivated, race to make more and stronger antibodies. WHAT ABOUT NATURAL IMMUNITY? A prior infection doesn’t seem to offer much protection against an omicron infection although, like with vaccination, it may reduce the chances of severe illness. In South Africa, where omicron already has spread widely, scientists reported a jump in reinfections that they hadn’t seen when two previous mutants, including delta, moved through the country. In Britain, a report from the Imperial College of London on Friday found the risk of reinfection from omicron was five times higher compared to the earlier delta variant. Health experts say anyone who’s survived a bout of COVID-19 still should get vaccinated, because the combination generally offers stronger protection. WHY ELSE DOES OMICRON SPREAD SO FAST? Scientists are trying to decode the dozens of mutations that omicron carries to figure out what else is going on. Researchers in Hong Kong recently reported hints that omicron may multiply more quickly in the airway than delta did, although not as efficiently deep in the lungs. What scientists can't measure is human behavior: Many places were relaxing restrictions, winter forced gatherings indoors and travel has jumped right as omicron began spreading. IS OMICRON CAUSING MILDER ILLNESS? It’s still too early to know — especially given that if the vaccinated get a breakthrough infection, it should be milder than if omicron attacks the unvaccinated. Early reports from South Africa suggested milder illness but doctors were unsure whether that’s because the population is fairly young — or that many retained some protection from a recent delta infection. And that British study found no evidence that omicron has been milder than delta in Britain, even with young adults — who would be expected to have milder illness — having higher rates of infection with omicron. "There’s a hint, and I think many of us are hopeful, that omicron will be less severe. But I don’t think we can bet the farm on that. We’re still talking about SARS CoV-2, a virus that has killed millions of people,” said Dr. Jacob Lemieux, who monitors variants for a research collaboration led by Harvard Medical School. Also read: Booster at least 80% effective against severe Omicron WHO’S MOST AT RISK? Based on the behavior of other variants, “if you’re older, if you have underlying conditions, if you’re obese, you’re more likely to have severe disease. I don’t think it’s going to be any different” than other variants, said Dr. Carlos del Rio of Emory University. But even if you don’t get very sick, an omicron infection could certainly ruin the holidays. Experts agree that in addition to getting vaccinated and boosted, it's wise to get back to the basics of protection: Wear masks indoors, avoid crowds and keep your distance.

The U.S. on Friday opened COVID-19 booster shots to all adults and took the extra step of urging people 50 and older to seek one, aiming to ward off a winter surge as coronavirus cases rise even before millions of Americans travel for the holidays. Until now, Americans faced a confusing list of who was eligible for a booster that varied by age, their health and which kind of vaccine they got first. The Food and Drug Administration authorized changes to Pfizer and Moderna boosters to make it easier. Under the new rules, anyone 18 or older can choose either a Pfizer or Moderna booster six months after their last dose. For anyone who got the single-dose Johnson & Johnson vaccine, the wait already was just two months. And people can mix-and-match boosters from any company. READ:  Pfizer asks FDA to OK COVID-19 booster shots for all adults “We heard loud and clear that people needed something simpler — and this, I think, is simple,” FDA vaccine chief Dr. Peter Marks told The Associated Press. The Centers for Disease Control and Prevention had to agree before the new policy became official late Friday. CDC Director Dr. Rochelle Walensky endorsed a recommendation from her agency's scientific advisers that — in addition to offering all adults a booster — had stressed that people 50 and older should be urged to get one. “It’s a stronger recommendation,” said CDC adviser Dr. Matthew Daley of Kaiser Permanente Colorado. “I want to make sure we provide as much protection as we can.” The CDC also put out a plea for those who had previously qualified but hadn't yet signed up for a booster to quit putting it off — saying older Americans and people with risks such as obesity, diabetes or other health problems should try to get one before the holidays. The expansion makes tens of millions more Americans eligible for an extra dose of protection. The No. 1 priority for the U.S., and the world, still is to get more unvaccinated people their first doses. All three COVID-19 vaccines used in the U.S. continue to offer strong protection against severe illness, including hospitalization and death, without a booster. But protection against infection can wane with time, and the U.S. and many countries in Europe also are grappling with how widely to recommend boosters as they fight a winter wave of new cases. In the U.S., COVID-19 diagnoses have climbed steadily over the last three weeks, especially in states where colder weather already has driven people indoors. And about a dozen states didn't wait for federal officials to act before opening boosters to all adults. “The direction is not a good one. People are going inside more and, ‘oops,’ next week happens to be the largest travel week of the year, so it probably makes sense to do whatever we can here to try to turn the tide,” Marks told the AP. READ:  Are COVID-19 boosters the same as the original vaccines? Vaccinations began in the U.S. last December, about a year after the coronavirus first emerged. More than 195 million Americans are now fully vaccinated, defined as having received two doses of the Pfizer or Moderna vaccines or the single-dose J&J. More than 32 million already have received a booster, a large proportion — 17 million — people 65 or older. Experts say that's reassuring as seniors are at particularly high risk from COVID-19 and were among the first in line for initial vaccinations Teen boosters aren't yet under discussion, and kid-sized doses of Pfizer's vaccine are just now rolling out to children ages 5 to 11. The Biden administration had originally planned on boosters for all adults but until now, U.S. health authorities — backed by their scientific advisers — had questioned the need for such a widespread campaign. Instead, they first endorsed Pfizer or Moderna boosters only for vulnerable groups such as older Americans or those at high risk of COVID-19 because of health problems, their jobs or their living conditions. This time around, the experts agreed the overall benefits of added protection from a third dose for any adult — six months after their last shot — outweighed risks of rare side effects from Moderna's or Pfizer's vaccine, such as a type of heart inflammation seen mostly in young men. Several other countries have discouraged use of the Moderna vaccine in young people because of that concern, citing data suggesting the rare side effect may occur slightly more with that vaccine than its competitor. Pfizer told CDC's advisers that in a booster study of 10,000 people as young as 16, there were no more serious side effects from a third vaccine dose than earlier ones. That study found a booster restored protection against symptomatic infections to about 95% even while the extra-contagious delta variant was surging. Britain recently released real-world data showing the same jump in protection once it began offering boosters to middle-aged and older adults, and Israel has credited widespread boosters for helping to beat back another wave of the virus. While the vaccines spur immune memory that protects against severe disease, protection against infection depends on levels of virus-fighting antibodies that wane with time. No one yet knows how long antibody levels will stay high after a booster. But even a temporary boost in protection against infection may help over the winter and holidays, said CDC's Dr. Sara Oliver. Some experts worry that all the attention to boosters may harm efforts to reach the 47 million U.S. adults who remain unvaccinated. There’s also growing concern that rich countries are offering widespread boosters when poor countries haven’t been able to vaccinate more than a small fraction of their populations. “In terms of the No. 1 priority for reducing transmission in this country and throughout the world, this remains getting people their first vaccine series,” said Dr. David Dowdy of Johns Hopkins Bloomberg School of Public Health.

Johnson & Johnson asked the Food and Drug Administration on Tuesday to allow extra shots of its COVID-19 vaccine as the U.S. government moves toward expanding its booster campaign to millions more vaccinated Americans. J&J said it filed a request with the FDA to authorize boosters for people 18 and older who previously received the company's one-shot vaccine. While the company said it submitted data on several different booster intervals, ranging from two to six months, it did not formally recommend one to regulators. Last month, the FDA authorized booster shots of Pfizer’s vaccine for older Americans and other groups with heightened vulnerability to COVID-19. It’s part of a sweeping effort by the Biden administration to shore up protection amid the delta variant and potential waning vaccine immunity. Read:FDA adds warning about rare reaction to J&J COVID-19 vaccine Government advisers backed the extra Pfizer shots, but they also worried about creating confusion for tens of millions of other Americans who received the Moderna and J&J shots. U.S. officials don't recommend mixing and matching different vaccine brands. The FDA is convening its outside panel of advisers next week to review booster data from both J&J and Moderna. It’s the first step in a review process that also includes sign-off from the leadership of both the FDA and the Centers for Disease Control and Prevention. If both agencies give the go-ahead, Americans could begin getting J&J and Moderna boosters later this month. J&J previously released data suggesting its vaccine remains highly effective against COVID-19 at least five months after vaccination, demonstrating 81% effectiveness against hospitalizations in the U.S. But company research shows a booster dose at either two or six months revved up immunity even further. Data released last month showed giving a booster at two months provided 94% protection against moderate-to-severe COVID-19 infection. The company has not yet released clinical data on a six-month booster shot. FDA's advisers will review studies from the company and other researchers next Friday and vote on whether to recommend boosters. The timing of the J&J filing was unusual given that the FDA had already scheduled its meeting on the company's data. Companies normally submit their requests well in advance of meeting announcements. A J&J executive said the company has been working with FDA on the review. Read: To launch J&J Covid shot in India, Biological E begins talks with govt lab to test vaccine “Both J&J and FDA have a sense of urgency because it’s COVID and we want good data out there converted into action as soon as possible,” said Dr. Mathai Mammen, head of research for J&J's Janssen unit. The vaccine from the New Brunswick, New Jersey, company was considered an important tool in fighting the pandemic because it requires only one shot. But its rollout was hurt by a series of troubles, including manufacturing problems at a Baltimore factory that forced J&J to import millions of doses from overseas. Additionally, regulators have added warnings of several rare side effects to the shot, including a blood clot disorder and a neurological reaction called Guillain-Barré syndrome. In both cases, regulators decided the benefits of the shot still outweighed those uncommon risks. Rival drugmakers Pfizer and Moderna have provided the vast majority of U.S. COVID-19 vaccines. More than 170 million Americans have been fully vaccinated with the companies’ two-dose shots while less than 15 million Americans got the J&J shot.

U.S. experts are expected to recommend COVID-19 vaccine boosters for all Americans, regardless of age, eight months after they received their second dose of the shot, to ensure lasting protection against the coronavirus as the delta variant spreads across the country. Federal health officials have been actively looking at whether extra shots for the vaccinated would be needed as early as this fall, reviewing case numbers in the U.S. as well as the situation in other countries such as Israel, where preliminary studies suggest the vaccine’s protection against serious illness dropped among those vaccinated in January. An announcement on the U.S. booster recommendation was expected as soon as this week, according to two people familiar with the matter who spoke to The Associated Press on the condition of anonymity to discuss internal deliberations. Doses would only begin to be administered widely once the Food and Drug Administration formally approves the vaccines. That action is expected for the Pfizer shot in the coming weeks. READ: US okays Covid booster dose for those with weak immune systems Last week, U.S. health officials recommended boosters for some with weakened immune systems, citing their higher risk of catching the virus and evidence that the vaccines’ effectiveness waned over time. The director of the National Institutes of Health, Dr. Francis Collins, said Sunday the U.S. could decide in the next couple weeks whether to offer coronavirus booster shots to Americans this fall. Among the first to receive them could be health care workers, nursing home residents and other older Americans, who were some of the first Americans to be vaccinated once the shots received emergency use authorization last December. Since then, more than 198 million Americans have received at least one dose of a COVID-19 vaccine according to the Centers for Disease Control and Prevention, with more than 168 million fully vaccinated. Still, the country is experiencing a fourth surge of virus cases due to the more transmissible delta variant, which is spreading aggressively through unvaccinated communities but is also responsible for an increasing number of so-called “breakthrough infections” of fully vaccinated people. Israel, which exclusively administered the Pfizer shot, has been offering a coronavirus booster to people over 60 who were already vaccinated more than five months ago in an effort to control its own surge in cases from the delta variant. READ: Why might COVID-19 vaccine boosters be necessary? For months, officials had said data still indicated that people remain highly protected from COVID-19, including the delta variant, after receiving the two-dose Pfizer or Moderna regimen or the one-shot Johnson & Johnson vaccine. But U.S. health officials made clear Sunday they are preparing for the possibility that the time for boosters may come sooner than later. “There is a concern that the vaccine may start to wane in its effectiveness,” Collins said. “And delta is a nasty one for us to try to deal with. The combination of those two means we may need boosters, maybe beginning first with health care providers, as well as people in nursing homes, and then gradually moving forward” with others, such as older Americans who were among the first to get vaccinations. He said because the delta variant only started hitting the U.S. hard in July, the “next couple of weeks” of case data will help the U.S. make a decision. Officials were continuing to collect information as well about the J&J vaccine, which was only approved in the U.S. in late February, to determine when to recommend boosters, one of the officials said. The White House has said that even though the U.S. has begun sharing more than 110 million vaccine doses with the world, the nation has enough domestic supply to deliver boosters to Americans should they be recommended by health officials. Global health officials, including the World Health Organization, have called on wealthier and more-vaccinated countries to hold off on booster shots to ensure the supply of first doses for people in the developing world.