What Happens If I Skip My Second COVID-19 Vaccine Shot?

Since December 2020, over 500 million doses of the COVID-19 vaccines have been administered in the U.S. Over 60% of the population is now fully vaccinated, but there are still people who may have who have skipped their second dose — meaning that they’re only partially protected.

For some, it may have been a bad experience with their first dose. For others, it may be the perception that one dose is enough because they caught COVID-19 between shots. Either way, you won’t get the full benefit of the two-dose series if you skip your second shot.

Here we’ll cover what you need to know if you’ve skipped your second shot and what steps you can take to get back on track.

Why do COVID-19 vaccines require two shots?

For the mRNA (messenger RNA) vaccines, the first vaccine dose is meant to prime your immune system. It works by instructing your cells to make the coronavirus spike protein — an important part of the virus that helps it infect our cells. If you haven’t been exposed to the virus before, this will be the first time your body sees the protein, and your immune system will be alerted to take care of it.

But when you get your second dose, your body already knows that the spike protein is something that doesn’t belong. This causes an even stronger reaction, resulting in a higher level of protection against COVID-19. 

It isn’t unusual for vaccines to require multiple doses for us to get the full benefit. In fact, many of the vaccines recommended during childhood require at least two doses. And like the COVID-19 vaccines, each dose is spaced apart safely so we get optimal protection.

Why is the second shot worse?

As your immune system is mounting a response after your first dose, you might get a headache, feel tired, or even develop a low fever. This is typical — it’s called reactogenicity, and it can be a sign that the vaccine is working. But if you feel fine after your dose, that doesn’t mean that the vaccine isn’t doing its job. 

When you get your second shot, your body recognizes the spike protein from before and reacts quickly. Because of this, the side effects from the second shot can be stronger in some people. 

If you’ve already had COVID-19, you might actually react more strongly to the first dose because your body has already seen the spike protein from your previous infection. In this case, your first dose is acting like your second dose. That said, it’s still recommended that you get the second shot.

So if you’re concerned about side effects, keep in mind that they can be a sign that the vaccine is working and will typically resolve within a few days. And some people don’t have any side effects at all. 

Do all available COVID-19 vaccines require two doses?

The FDA has approved the Pfizer and Moderna COVID-19 vaccines for use in the U.S. They’ve also authorized the Johnson & Johnson COVID-19 vaccine. The CDC currently recommends the Pfizer and Moderna vaccines over the Johnson & Johnson vaccine in most situations.

The mRNA vaccines, Pfizer and Moderna, both require two doses for full protection. The main difference is timing — you’ll wait 3 weeks before your second Pfizer dose and 4 weeks before your second Moderna dose.

The Johnson & Johnson vaccine, on the other hand, only requires one shot for the primary vaccine series. But a booster dose is recommended at least 2 months later.

How long after receiving the second dose are you protected?

According to the CDC, you’re considered to be fully vaccinated 2 weeks after your second dose. But if you have a weakened immune system, you may need an additional dose 28 days after your second shot to be fully vaccinated.

Once you’ve completed your primary vaccine series, it’s important to keep up-to-date with your shots. This may include booster doses as you become eligible for them. Getting your recommended boosters can help keep you better protected against COVID-19.

What happens if you don’t get the second dose?

If you skip your second shot, the short answer is that you aren’t getting the best protection from the two-dose series. All of the clinical trial data that measured effectiveness is based on people getting both doses. So, we don’t know the level of protection you’ll get from only one shot.

Scientists continue to track how well the vaccines work over time, especially as new COVID-19 variants are identified. The data continues to show that being fully vaccinated makes a difference in protecting against serious illness from COVID-19. And if you’ve already had COVID-19, getting both of your shots provides even more protection. 

In other words, whether or not you’ve had COVID-19 in the past, you’ll want to complete the full two-dose series.

Can you get COVID-19 after the first or second dose?

While the two-dose vaccine series can help provide protection against COVID-19, there are a few things to keep in mind about your infection risk at different points in the vaccination process.

You can get COVID-19 before you’re fully vaccinated

While your immune system is building up protection against the disease, it’s possible to get COVID-19 at any point before 2 weeks after your second dose. You can get infected, and even sick, in between doses or right after your second shot.

Plus, COVID-19 symptoms can take a while to show up — even 14 days after you’ve been exposed to the virus. If you get sick during this time, that means it’s also possible that you were infected before you got your first shot.

If this happens, you’ll still want to get your second shot. However, you’ll need to make sure that your symptoms have resolved and that you’ve met quarantine requirements first.

You can get COVID-19 even if you’re fully vaccinated

Yes, this is true. That’s because none of the vaccines will prevent 100% of COVID-19 cases. When a fully vaccinated person tests positive for COVID-19, it’s called a breakthrough infection.

But getting vaccinated is still worth it. While you still might get sick, there’s less of a chance of ending up in the hospital or dying from COVID-19.

What should you do if you miss your second COVID-19 shot?

Perhaps you’re outside of the recommended second shot window and assume that there’s no longer a benefit. You’ll want to get it as close to the window as possible, but you can receive it at any time after and still be considered fully vaccinated.

Although we don’t have information about how effective the vaccine will be outside of the window, it’s better to get it late than not at all. And you don’t need to start your doses over, either. The bottom line is that if you didn’t get your second shot on time, you’ll want to get it as soon as possible. 

If you didn’t get your second shot because you developed COVID-19 at some point during the vaccination process, it’s still recommended that you get your second dose. As mentioned above, you’ll need to wait until you’ve recovered from your illness and have met quarantine requirements before making your appointment.

However, if your provider instructed you to skip the second shot due to an allergic reaction, you should follow their instructions.

How do I schedule an appointment for my second shot?

If you’ve been trying to get a second shot but you’re having difficulty finding a site with your vaccine brand, there are resources to help. 

To start, you can reach out to your local health department for assistance. You can also search for the product you need within your state here and browse by pharmacy to see appointment openings in your area.

Should I get a booster shot?

Once you’ve completed your two-dose series, you may be debating whether or not to get a booster shot. Keep in mind that protection from vaccines can go down over time, and the COVID-19 vaccines are no exception. And greater amounts of protection may be needed against new variants, too. Booster shots help “boost” your level of protection.

A booster shot is currently recommended for everyone who’s eligible. This depends on your age and when you finished your primary vaccine series. Getting your booster shot on time can help lower the risk of serious illness from COVID-19.

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Written by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. A pulmonologist and hospitalist, she practiced and taught clinical medicine at hospitals in London for a decade before entering a career in health education and technology.

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