The updated coronaviruses vaccine targeting the Omicron variant is Moderna's lead candidate to be used as a U.S. booster shot in the fall.

A booster dose combining the original vaccine with one specifically against Omicron was tested by researchers. The combination produced 1.75 times the amount of neutralizing antibodies against Omicron as the existing Moderna vaccine did alone.

While those results seem encouraging on their face, many experts worry that the virus is evolving so fast that it is out pacing the ability to modify vaccines, at least as long as the US relies on human clinical trials for results.

Moderna found that the updated vaccine produced a stronger immune response than the existing vaccine a month after it was given. There were three earlier shots of Moderna's vaccine.

Some vaccine experts say what matters is how well a new booster would protect against the latest subvariants, not Omicron itself. The two subvariants that were first detected in South Africa are now accounting for 13 percent of new cases in the United States. They could out compete the two other Omicron subvariants within a month.

The updated vaccine did not work against BA.4. Researchers are still gathering data on those and other subvariants, according to the firm's president.

He said that a very small sample, together with isolated other studies, suggested that the levels of neutralizing antibodies triggered by the updated vaccine were two to three times lower against the BA.4 and BA.5 subvariants.

Moderna's researchers can't say if the new vaccine will offer more protection than the old one.

The newer versions of Omicron seem to spread more quickly and may be better at evading the immune system. They are not certain if they cause more severe disease. The chief medical adviser to the White House said in an interview Tuesday that there had been a slight increase in hospitalizations in South Africa.

Some vaccine experts say it makes sense to target the most recent versions of the virus rather than the ones that will be overtaken soon.

Moderna and Pfizer, the makers of the other main coronaviruses vaccine in the United States, do not have enough time to run more human clinical trials and still make shots before the fall, when the Biden administration is hoping to be able to offer an updated vaccine to counter what

It could force regulators to use data from laboratory tests and trials involving animals instead of robust human trials. It is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556 is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556

The Food and Drug Administration's outside advisers are scheduled to meet on June 28 to discuss which vaccine formula would work best as a fall booster.

The final decision is always left to the F.D.A. The F.D.A. will probably keep as many irons as possible. They may need to use laboratory data and possibly animal data as alternative pathways of decision.

He said that people who are very concerned about protecting themselves will accept a booster with no long human trials.

The trial of the vaccine targeting Omicron started in February. The participants were all older than 57. After receiving two shots of Moderna's existing vaccine, all volunteers were given a booster dose eight months later.

The first booster was given to 377 volunteers and the second booster was given to 437. The updated booster produced a stronger immune response among those who had been exposed to the virus and those who hadn't.

According to data released by Moderna, the people who got the updated booster had a higher level of neutralizing antibodies than the people who got the existing booster. Antibodies are the first line of defense against infections from the coronaviruses. The tests that defend against Covid-19 disease were not measured.

The results were described as encouraging by Dr. Paul Burton. He said that this is a turning point in the fight against the virus because they can adapt to a variant. It works, that's what I say.

A less than twofold increase in neutralizing antibodies over the existing vaccine is only a small benefit according to John Moore.

He asked if that justified changing vaccine composition given the cost and the logistical aspects of it. The argument will be about that.

Results from Pfizer and BioNTech's vaccine testing are expected soon.

Moderna released preliminary results on a vaccine retooled to attack theBeta variant. The combination provided a stronger defense against the Delta and Omicron variant. An Omicron vaccine was expected to be a better candidate.