We're nearly three years in and continuing to discover fallout. Recent studies suggest that menstrual cycles have been affected in women who have contracted Covid-19 or been vaccinated against it.

Anecdotally, women who have been vaccinated against Covid-19 have said that they've had an impact on their periods and symptoms that go with it they attribute to the vaccine. In some cases, this anecdotal reporting has been from those who have also/or contracted Covid-19 organically.

Reports of longer, heavier periods are widespread, and research is beginning to back that anecdotal reporting up.

Recent studies suggest that a woman's menstrual cycle can increase by up to a day immediately after they've been vaccinated, with a study of nearly 4,000 women finding that varied slightly on how many doses were given.

Though the cycles seemed to be longer overall, give or take a day, the research has found that the number of days a woman's period lasted has not seemed to change.

In the United Kingdom, a study of almost 20,000 women also noted a similar effect in cycle length but found that it was extended for longer in people who got both doses of the vaccine within the same menstrual cycle time period. The average cycle length was 3.7 days in those people.

Earlier this month, a paper published in the Journal of Infection and Chemotherapy appeared to reinforce those findings. Looking at predictions made on the menstrual cycle length of women in Japan before and after a Covid-19 vaccination, tye found the difference was about 1.9 days longer, being as high as 2.5 days longer in cycle length in women who had two doses in that same cycle.

The average length of cycle extension difference was 3.9 days.

Obviously variables like how long a period typically is or whether it's regular or not may play into this observation. The research finds that most people's cycles appear to go back to their normal after a couple of cycles.

Research also suggests that women may be more likely to experience varying period symptoms after they've been vaccinated. A study published in late December the journal Influenza and Other Respiratory Viruses, looked at data from over 5,000 women from six different Arab countries and found that those who were vaccinated appeared to have more frequent period symptoms. These included back pain, tiredness, nausea, pelvic pain, loose stools, and the need for unprescribed analgesics to cope with symptoms. The data also suggested vaccinated people had heavier flows with more days of bleeding, though the authors of the paper note that there is clearly the need for more data to continue to confirm those findings.

The study was based on long-term data from the Nurses' Health Study and showed that Covid-19 infection didn't affect cycle length. However, other studies with smaller sample sizes have found a small percentage of people who've contracted Covid-19 may experience cycle changes.

Clinicians theorize these changes may be due to the way the immune system responds, and as it may affect sex hormones that may in turn affect menstrual cycles. Some who experience inflammatory responses to the vaccine (or infection) may also experience ovarian and uterine differences in cycles.

Studies continue to look at the effect of both the vaccine and infection on menstrual cycles and fertility. Worldwide organizations still suggest that the benefits of vaccination and protection still outweigh the risks when it comes to health, particularly for pregnant women. A review published in the Archives of Gynecology and Obstetrics suggests that outcomes for those who are pregnant but not vaccinated may be poorer, with higher rates of hospitalization and critical care admission being necessary than in their vaccinated peers. Another study, however, found this to be not significant.