COVID-19 vaccine: Everything to know about your 2nd Pfizer or Moderna shot

SAN FRANCISCO -- Over the past few weeks, California has rapidly expanded its vaccine eligibility, meaning millions of people are getting a dose of the COVID-19 vaccine for the first time. That also means that millions of people are about to need their second dose of the COVID-19 vaccine pretty soon. If that's you, here's everything you need to know about getting your second dose.

When should I get my second dose?

If you received Pfizer as your first shot, you should schedule your second dose three weeks later. For Moderna, it's four weeks between doses. You can't mix and match; if you received the first dose of Pfizer, you need to get Pfizer for your second dose. The same goes for Moderna.

Is it too late to get my second dose?

You should try and stick to the recommended schedule as closely as possible (i.e. three weeks for Pfizer, four weeks for Moderna). According to the CDC, second doses administered four days earlier than the recommended timeframe are still considered valid. This is not recommended, however.

If your three-week or four-week window has expired, it might not be too late to get that second dose. The CDC still suggests getting your second dose up to six weeks (or 42 days) after your first dose. After that, it's not recommended at this time -- not because there's evidence it would be harmful, but rather there's not enough information on how effective it would be at that point.

If it's been longer than six weeks, the CDC does not advise you start the whole process over. The agency says more guidance on this is forthcoming.

How do I schedule a second dose?

If you scheduled an appointment on California's MyTurn site, you'll typically schedule both doses at the same time. You may also receive information on how to schedule your second dose on site while receiving the first shot.

If you still need a second appointment, reach out to the provider of your first dose, whether that be a pharmacy, health care provider or a county clinic.

Is the second dose of the COVID-19 vaccine the same as the first?

Yes, the contents of your second dose are the same as what you received in the first dose.

Do I need to get my second dose at the same location as my first dose?

For those of you that trekked far from home just to score that first dose, you're not required to do that again the second time around. "There is no requirement to return to the same location of the first dose for the recipient's second dose," said Sam Gallegos, a spokesperson for California's COVID-19 vaccine task force.

Gallegos said she hasn't heard of anyone being turned away because they didn't get their first dose at that same site. Just remember that if you don't plan to return to a vaccination site for your second dose, cancel your appointment so someone else has a chance to take that spot.

How effective is just one dose?

One CDC study of nearly 4,000 medical workers found that one dose of the vaccine was about 80% effective at preventing COVID-19 infection after two weeks.

Why does the second dose cause more side effects?

Fever, chills and body aches are all normal side effects from the COVID-19 vaccine. They are often stronger after the second dose because your body's immune response is stronger.

"The way I think about them is it is a sign that it's working," UCSF's Dr. Bob Wachter told ABC7. He said young people seem to have even stronger side effects than older people because young people have a "stronger, more exuberant immune system" that can kick into overdrive.

If you don't have side effects, does that mean the vaccine isn't working? No, says Dr. Wachter. "Not having side effects, you should consider yourself lucky, but the vaccine seems to work as well in people who didn't have side effects."

What do I do if I missed my second dose appointment?

You should contact the provider and reschedule an appointment as close as you can to the suggested time frame (three weeks for Pfizer, four weeks for Moderna).

What do I do if I lost my vaccination card?

First off, you should try contacting the vaccine provider of your first dose to see if they can access your vaccination record and get you another copy. If you can't get a hold of them, you should contact the California Department of Public Health. If you've done everything you can to get a copy and are still unsuccessful, the CDC suggest contacting a vaccination provider directly so you can still get your second shot.

When am I considered fully vaccinated?

The CDC considers you fully vaccinated when it has been two weeks since your second dose of Pfizer or Moderna, or if it's been two weeks since you received the single dose Johnson & Johnson vaccine.

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