Thinking about skipping the second dose? You should reconsider

Last Modified: 9/13/2021


This post was written by Lisa Hatcher, MD, PPG – Family Medicine.

The COVID-19 vaccine is proving to be a promising tool in restoring our pre-pandemic activities and behaviors. While there is a single-dose option for those who wish to receive the vaccine, most of the vaccines being administered are given in two doses. It is imperative that those who receive the latter complete the entire vaccine series. Let’s explore why this is so important.

Why are some COVID vaccines two doses?

No vaccine is 100% effective. As vaccines are developed, they are tested for effectiveness. As the mRNA vaccines (Pfizer and Moderna) were tested, it was found that one dose provided some short term protection, but a second dose increased the effectiveness and durability of the vaccines.

How much time can pass between the first dose and the second dose?

Time between first and second doses varies by type of vaccine. It is important to follow the manufacturer’s recommendations, as they are based on the performance of the vaccine in research and development studies, which include clinical trials. 

The Pfizer-BioNTech COVID-19 vaccines should be spaced at a three-week interval and the Moderna vaccine at a four-week interval. If you miss the date for your second dose, reschedule as soon as possible. The current recommendation is that you should receive the second dose within at least six weeks.

Why is it important not to skip the second dose?

If you skip the second dose, you will not achieve the maximum vaccine efficacy and will be at higher risk for vaccine failure and contracting the virus. The Pfizer vaccine effectiveness in a fully vaccinated person (two weeks after the second dose) is 95%. The Moderna vaccine effectiveness in a fully vaccinated person is 94%.

What if I experienced side effects after the first dose?

It depends on what those side effects were, but if someone had symptoms severe enough that they felt they could not work, I would recommend scheduling the second vaccine on a day when you could take a couple days off from work. For instance, if you typically have the weekend off, you may want to schedule the vaccine on a Friday so that you have a couple days to recover. I would also recommend that you hydrate well the days before, during and after the vaccination and that you plan to get a full eight hours of sleep each of those nights. It is fine to treat any symptoms with acetaminophen (Tylenol®) or ibuprofen (Advil®/Motrin®). I do not recommend pre-treating.

How effective or how much protection will I get from just the first dose alone?

The first dose of a two-dose COVID-19 vaccine does provide some protection. Clinical trials showed this might be as high as 75%. However, as more of the population is vaccinated, real world statistics may give us different results.

Are there any instances when someone should not get the second dose?

You should not receive the second dose if you have a severe (anaphylactic) reaction to the first dose. A severe reaction is one that requires a visit to the Emergency Room for medical intervention or the use of epinephrine.

You should not receive the second dose if you have an immediate reaction to any component of the vaccine. An immediate reaction is defined as one that occurs within four hours of receiving the vaccine. This might include hives, swelling or wheezing.  

Is it ever too late to get the second dose?

Probably. At this time, all efforts should be made to get the vaccine in the recommended timeframe and at least by six weeks after the first dose. As real world statistics accumulate, a new (better) answer may be available.


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