Two of the currently approved COVID-19 vaccines, the Pfizer and Moderna vaccines, provide strong protection against COVID-19, but gaining the full protective benefit of either vaccine requires getting two shots — and the timing between these doses is important.

The recommended interval between the first and second dose is:

• Three weeks (21 days) apart for Pfizer-BioNTech
• Four weeks (28 days) apart for Moderna
  
  

And while it's best to get your second dose on time...stuff happens.

Maybe you got COVID-19 shortly after your first dose and need to recover before getting your second one. Maybe you even received monoclonal antibody therapy or convalescent plasma while ill and need to wait 90 days before your second dose. Or maybe a personal crisis or natural disaster prevented you from making it to your appointment for your second dose.

So, what happens if your second COVID-19 vaccine dose is delayed due to something unavoidable?

Here's what you need to know if you miss your second COVID-19 vaccine dose

If a situation that's out of your control arises and causes you to miss your second dose, don't panic.

"It's best to get your second dose as close to the recommended interval as possible. But, if a delay is unavoidable, missing this window doesn't mean you've missed your only chance of getting your second dose. It also doesn't mean you need to start your vaccination plan over completely," says Dr. Ashley Drews, medical director of infection prevention and control at Houston Methodist.

According to the CDC, when following the recommended guidelines isn't feasible, the second dose of either the Pfizer or Moderna vaccine can be administered up to six weeks after the first one.

"What we don't know is how effective either vaccine is when delayed beyond six weeks, but getting your second dose is still recommended and likely to be beneficial," Dr. Drews says. "Even if your second dose is significantly delayed, you do not need to start the vaccine series all over. You should just get the second dose to complete the series as soon as possible."

The bottom line: If you missed your appointment for your second dose, contact the vaccine distributor to reschedule as soon as possible.

When it comes to getting your second dose on time, take steps to avoid the avoidable

There will always be things in life you can't control, so it's important to take control of the things that you can.

Since the timing between COVID-19 vaccine doses may impact the vaccine's effectiveness, it's important to take steps to help ensure you get your second dose on schedule.

Here are three things you can do to help make sure you get your second dose on time:

1. Check your calendar before scheduling your first dose. When making your appointment for your first dose, be sure that in three weeks' time (Pfizer) or four weeks' time (Moderna) you're actually available to come in for your second one. You may not know which vaccine you're getting ahead of time, so be sure you're free and available both three and four weeks out.
   
   
2. Leave your first appointment with your second appointment scheduled. The process for scheduling your second dose will vary depending on where you get vaccinated, but don't hesitate to ask questions about the process if it's not already made clear to you. Ideally, don't leave your first appointment without having your second one scheduled.
   
   
3. Know which vaccine you received. The Pfizer and Moderna vaccines have different recommended dosage intervals in the initial series. While at your appointment, don't forget to ask which vaccine you're receiving. This information will help you stay on top of the timing for your second dose, especially if your vaccination site doesn't allow you to schedule your second dose immediately.