Nearly half of the women who took part in a recent study and had regular periods at the time of the survey said their periods were heavier after they got the Covid-19 vaccine. 

This current study, the largest one of its kind to date, builds on previous research emphasizing the transitory effects of Covid-19 vaccinations on menstrual periods.

The new study began in April 2021 by the researchers at the University of Illinois at Urbana-Champaign and Washington University School of Medicine in St. Louis, when people started reporting unexpected bleeding and higher flow after receiving vaccinations. On the other hand, the reply to these tales at the time was that no data tied menstrual changes to vaccination.

The researchers analyzed data from three consecutive cycles before vaccination and from three cycles after that – including the cycle or cycles in which vaccination took place – to understand how vaccination’s periods were affected. The participants who had not been vaccinated had their data taken for six rounds in a row.

What Were the Most Important Findings?

When compared to women who were not vaccinated against COVID-19, women who received one dose of a COVID-19 vaccine during a single menstrual cycle had a slight increase in cycle length – meaning a longer time between bleeding – that was just over half a day longer, on average. This was in comparison to women who did not receive the vaccine.

This was found in comparison to women who were not vaccinated. Even while these alterations were statistically significant, the fact that there is a natural fluctuation in the cycles of unvaccinated women meant that a large number of them similarly experienced these changes from one month to the next. 

There was no difference in the proportion of persons who experienced a clinically relevant change in cycle length of eight days or more. Neither group experienced a difference.

Although 10% of these women saw a bigger shift in cycle length of eight days, those who received two vaccine doses within the same menstrual cycle experienced a slightly longer rise in cycle length, equivalent to two days. However, ten percent of these women experienced a larger shift in cycle length of eight days or more. The fact that these modifications went back to how they were so fast over subsequent cycles gives credence to the theory that they were just transient.

What is Their Theory About this Occurrence?

The chemical crosstalk between a person’s brain and ovaries controls the timing of their menstrual cycles. This chemical crosstalk can be interrupted by either physical or emotional stress. Because it is intended to provoke a robust immunological response, vaccination has the potential to act as a source of physical stress.

It has been reported in the past that the human papillomavirus (HPV) vaccine may have a temporary effect on menstrual cycles. In spite of this, there is no evidence to show that it has any impact on fertility.

What Do these Repercussions Mean?

The researchers noted that the increase they observed was well within the range of normal variability and that most women wouldn’t even notice if their period arrived half a day later than normal.

Menstrual cycles in women typically vary a small amount from month to month, and they pointed out that the increase they observed was well within the range of normal variability. The fact that women’s periods returned to normal within a few cycles suggests that this was only a temporary change; however, the researchers cautioned that they do not yet have sufficient data about subsequent cycles to say this with absolute certainty.

The fact that women’s periods returned to normal within a few cycles suggests that this was only a temporary change. Because the women in this study were predominantly White, college-educated, and had lower-than-average body mass indexes (BMIs). Only those women with consistently normal menstrual cycle lengths were chosen for analysis; the findings may not apply to the population as a whole in the United States or anywhere else in the world; similarly, the findings may not apply to women who have underlying health conditions that affect their menstrual cycles.

Despite this, the researchers felt that their findings provided a sense of comfort. They claim that their findings show that there is “no population-level clinically relevant difference in menstrual cycle length linked with COVID-19 immunization.