[News] Covid-19 Live Updates: What We Know About the C.D.C.’s Vaccine Plans

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In planning documents sent last week to public health agencies around the country, the U.S. Centers for Disease Control and Prevention described preparations for two coronavirus vaccines simply referred to as Vaccine A and Vaccine B.

But the technical details, including the time between doses and storage temperatures, match well with the two vaccines furthest along in U.S. clinical tests, made by Moderna and Pfizer.

Some experts are concerned about what they see as a rushed process. “It’s hard not to see this as a push for a pre-election vaccine,” said Saskia Popescu, an infection prevention epidemiologist in Arizona.

Still, public health experts agree that agencies at all levels of government should urgently prepare for what will eventually be a vast, complex effort to vaccinate hundreds of millions of Americans.

Here are some answers to some basic questions people may have.

How do these vaccines work?

Moderna and Pfizer are testing a new kind of vaccine that has never before been approved for use by people. It contains genetic molecules called messenger RNA that are injected into muscle cells, which treat them like instructions for building a protein.

How well do they work?

Once designed, vaccines go through four testing stages. In the preclinical stage, researchers test them on animals. For Covid-19, these include hamsters and genetically modified mice, both of which can experience some of the same symptoms as humans.

If these tests yield promising results, then the vaccines go into three phases of clinical trials in people.

Moderna and Pfizer are currently testing their candidates in Phase 3 trials. In their earlier human studies, neither vaccine produced serious side effects. Both vaccines provoked people’s immune systems to make antibodies that can neutralize the coronavirus.

Could a vaccine be approved before clinical trials are completed?

Some federal health officials have said a vaccine could be made available to at least some groups before clinical trials are completed. An independent Data and Safety Monitoring Board is charged with checking in on clinical trials to ensure there are no serious safety issues.

If the vaccine is harming participants, the trial may be ended early. But if it appeared to be working well, the board could decide that it would no longer be ethical to continue giving some participants a placebo and end the trial early.

What have companies said about when their vaccines may be ready?

Pfizer recently said it was “on track” for seeking government review “as early as October 2020.” Moderna has said it expects to complete enrollment in its Phase 3 trial in September, but has not provided an estimate about when the vaccine might be ready for the public.

Federal officials said in May that the first doses of a vaccine being developed by AstraZeneca, in partnership with the University of Oxford, could be delivered by October. But AstraZeneca, which recently began Phase 3 trials in the United States, is now saying it could supply the first doses by the end of 2020.

How would a vaccine reach the public?

Normally, vaccine makers would wait for clinical trials to yield definitive results before moving forward with manufacturing. This time, many manufacturers have begun preparing in advance for production, getting money from governments to buffer the risk.