Your questions about COVID-19 vaccines answered

Millions of people around the United States and the world have been vaccinated against COVID-19, and the number of people being vaccinated each day continues to rise. President Biden has said that there should be enough vaccine for every American adult by the end of May.

In the U.S., three vaccines have been authorized for emergency use by the Food and Drug Administration: One is made by Pfizer-BioNTech, one by Moderna, and the latest by Johnson & Johnson. In California, healthcare workers, residents of long-term care facilities, people over 65, grocery store workers, teachers and others are eligible to sign up to be vaccinated.

Naturally, we all have questions about these developments.

Times readers have sent us dozens of submissions. To answer when and how you might get the vaccine, we have created county-by-county guides to help you navigate the often-confusing process of getting a shot. Many of you wanted to know about vaccine safety and about the science behind them. There are sections below on those topics.

Thanks for writing to us, and thanks for reading. You can send us more questions by email.

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Timeline and logistics | Safety | Vaccine science | Individual health

California has set up phases and tiers, as well as a service called MyTurn, to help people understand when they are eligible. L.A. County is communicating which subsets are currently eligible on its health department’s website.

Vaccines are safe. The COVID-19 vaccine from Pfizer and BioNTech that has been authorized for emergency use was subject to well-established procedures to evaluate vaccine safety by scientists at the U.S. Food and Drug Administration and elsewhere. The same is true about the Moderna vaccine and the Johnson & Johnson vaccine. Serious side effects have been exceedingly rare for Pfizer and Moderna. Johnson & Johnson’s vaccine hasn’t seen any serious side effects yet.

The FDA has never approved or authorized a vaccine that uses mRNA (see the section on vaccine science below for more on mRNA) before. Nevertheless, Commissioner Stephen Hahn said the technology has been around long enough that regulators are “very comfortable� with the platform.

Scientists had a head start in creating vaccines during this pandemic, based on earlier advances made against the SARS and MERS coronaviruses, which are relatives of the virus that has upended 2020.

BNT162b2, as the Pfizer-BioNTech vaccine is officially known, was developed in a matter of months thanks to a new method that uses a piece of the coronavirus’ genetic code rather than the virus itself. The Moderna vaccine works similarly.

Once the vaccine is injected into the body, the genetic payload — called messenger RNA, or mRNA — instructs cells to produce specific coronavirus proteins. The immune system responds by creating antibodies that are primed to attack the real coronavirus, said Dr. Bruce Walker, an immunology and infectious diseases researcher at Harvard and MIT.

“The process lasts in the body for about 36 hours,� Walker said. “Then the vaccine is degraded and essentially gone.� But the crucial antibodies remain.

We aren’t doctors, so we can’t answer questions about specific circumstances. Your best course of action is to discuss your health and any concerns about vaccination with your doctor.