Coronavirus Vaccination May Impact Women’s Periods

Since the COVID vaccines started rolling out, women have been asking how the vaccine impacts their periods. In the months following vaccination, some women reported their periods were late, while others reported heavier bleeding. Still others noticed irregular periods. And some post-menopausal women said they started bleeding again. 

It’s a question that’s on the minds of many women. And rightfully so.

In September, 2021 the National Institutes of Health (NIH) selected five institutions to conduct research to explore the potential impacts of COVID-19 vaccination on menstruation.

A study released on January 5th by The American College of Obstetricians and Gynecologists (ACOG) reported that women’s cycles did indeed change following vaccination.

On average, the study reported women experienced a temporary delay in their period by one day. 

As a sub-analysis, the study separated individuals who received both vaccine doses in one cycle and found that, on average, these women reported a delay in their period by two days. 

The study looked at records from nearly 4,000 U.S. women (almost 23,754 menstrual cycles) who had meticulously tracked their menstruation in real time ranging in ages from 18-45 and who tracked their periods over at least six months.

The findings of this study do not apply to all women equally. This was the average change reported.  A smaller group experienced a change of at least two days, while another group had overall cycles that were eight days longer than usual.

A second institution funded by the NIH, Oregon Health & Science University, Portland, noted in their study that menstrual cycles typically vary a small amount from month to month and the increase they saw was temporary and well within the range of normal variability.

Here is some further research and resources sharing information regarding the impact of the COVID vaccine on your menstrual cycle:

Obstetrics & Gynecology: Association Between Menstrual Cycle Length and COVID Vaccination. Posted January 5, 2022

MedRxiv: Characterizing menstrual bleeding changes occurring after SARS-Co-V-2 vaccination. Posted October 12, 2021.

COVID-19 vaccination associated with a small, temporary increase in menstrual cycle length, suggests NIH-funded study.

National Institutes of Health: NIH Funds studies to assess potential effects of COVID-19 vaccination on menstruation.

While these studies show patterns and variations in women’s menstrual cycles, let’s take this as a reminder for why tracking your own cycles is important.  What’s “normal” for one woman may not be “normal” for you.  When you consistently track your cycles (be it on a tracking app or a simple piece of paper), month after month, you can identify your patterns, consistencies and anomalies.

Here’s a simple tracking form that you can print and keep by your bathroom sink to track your cycle. 

Menstrual Cycle Tracking Form

Keep in mind that if your cycles are  changing dramatically in length from one month to the next, if your cycles are shorter than 21 days or longer than 35 days for several consecutive cycles, if you haven’t had a period in three months or longer, or if you have considerable pain or other unusual symptoms that accompany your period, consult your doctor.