疫苗制造商争先恐后地改变新冠疫苗

Vaccine makers are racing to make changes to their COVID-19 shots. They hope to make sure their vaccines are effective against the newest coronavirus threat even before it is clear a change is needed.

Experts doubt that current COVID-19 vaccines will become useless. But they say it is critical to see how fast companies can produce a new vaccine and prove it works. The newest version of the virus, omicron, appeared just a few weeks ago. But, scientists know it will not be the last.

Omicron "is pulling the fire alarm," said E. John Wherry. He is an immunologist at the University of Pennsylvania.

Wherry added, "Whether it turns out to be a false alarm, it would be really good to know if we can actually do this -- get a new vaccine rolled out and be ready."

It is too soon to know how vaccines will perform against omicron. Early data have been mixed: Lab tests suggest two Pfizer doses may not prevent an omicron infection but they could protect against severe illness. And a third booster shot may provide enough protection to do both.

The World Health Organization has appointed an independent scientific group to advise about possible vaccine changes. But officials have not directly said what conditions might necessitate making such changes.

Ugur Sahin is chief of BioNTech, Pfizer's vaccine partner. He said shortly before omicron's discovery that a company could propose to market a newer vaccine, "but what happens if another company makes another proposal with another variant? We don't have an agreed strategy."

If vaccines are to change, there is still another question: Should there be a separate omicron booster or a combination shot? And should a combination shot target the first version of the virus along with omicron, or the currently dominant delta variant plus omicron?

Companies are not starting from the beginning

COVID-19 vaccines work by causing production of antibodies that recognize and attack the spike protein that surrounds the new coronavirus. Many of the vaccines are made with new technology that is relatively easy to update, or change. The Pfizer and Moderna vaccines can be changed the fastest. Those vaccines include genetic material that directs the body to make harmless copies of the spike protein. That "messenger RNA" can be changed based on new versions of the virus.

Pfizer expects to have an omicron-specific vaccine candidate ready for the Food and Drug Administration to consider in March.

Moderna is predicting 60 to 90 days to have an omicron-specific candidate ready for testing. Other manufacturers that make COVID-19 vaccines, including Johnson & Johnson, also are working on possible updates.

Pfizer and Moderna already have successfully created experimental doses to match delta and another variant named beta. Those shots have not been needed. But the experiments offered valuable information.

Unclear if changes are needed

So far, the original vaccines have offered major protection against earlier variants. Pfizer's early lab testing, released Wednesday, suggests that might be the case with omicron, too.

Antibodies are not the only line of defense. Vaccines also cause the growth of T cells that can prevent serious sickness from infection. Pfizer's first tests showed, as expected, T cells do not seem to be affected by omicron.

Also, memory cells that can create new and somewhat different antibodies form with each dose.

How to tell if updates work

The U.S. FDA has said companies would not need massive studies of updated vaccines. Instead, they would only need small studies to measure if people given the updated shot have immune reactions comparable to the original, highly effective shots.

Wherry does not expect data from volunteers testing experimental omicron-targeted shots until at least February.

What about combination shots?

Flu vaccines protect against three or four different kinds of influenza in one shot. If a vaccine update is needed for omicron, officials will have to decide whether to make a separate omicron booster, add it to the original vaccine, or follow the flu model and try a combination.

There is some evidence that a COVID-19 combination shot could work. In a small Moderna study, a so-called bivalent booster containing the original vaccine and a beta-specific dose caused a bigger antibody jump than either an original Moderna booster or its experimental beta-specific shot.

And scientists already are working on next-generation vaccines that target parts of the virus less likely to change.

I'm Ashley Thompson.

And I'm Bryan Lynn.

The Associated Press reported this story. Ashley Thompson adapted it for VOA Learning English. Caty Weaver was the editor.

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doubt - v. to be uncertain about (something) : to believe that (something) may not be true or is unlikely

alarm - n. a warning of danger

immunologist - n. a doctor who treats health issues brought on by the immune system problems (immune system: the system that protects your body from diseases and infections)

booster (shot)- n. an extra amount of a substance (called a vaccine) that is injected with a needle into a person or animal to help protect against a particular disease

original - adj. happening or existing first or at the beginning