Covid vaccines can only affect menstrual cycles of women on contraception, study finds


Covid vaccines can only affect the menstrual cycles of women on contraception, suggests the first British study on the phenomenon.

Thousands of vaccinated women have complained of irregular periods after receiving the vaccine, with some postmenopausal women even claiming that it triggered vaginal bleeding.

But there has been no clear evidence of a link, although similar problems can arise with vaccines for other diseases.

Now researchers at Imperial College London believe they might have an answer after studying 1,200 women.

They found no definitive link between women receiving the jab and experiencing changes in the menstrual cycle.

But women who took birth control such as the pill were more likely to have heavier or lighter periods than normal, compared to those who did not.

This was the case with the three vaccines used in the rollout in Britain – AstraZeneca, Pfizer and Moderna.

The graphs above show the proportion of women who reported that their period was early, one-time, or late after receiving a Covid vaccine (blue bars) and that it was heavier, the same, or lighter than usual (bars red). Groups are divided by menstrual cycles in women who were not using contraception (marked as cycle) and using contraception (marked as hormonal contraception). They suggest that women who used contraception were more likely to have heavier or lighter periods after being vaccinated compared to those who were not.

The graphs above show the proportion of women who reported the timing (blue bars) or flow (red bars) of their menstrual cycle by medical condition.  It shows that those with endometriosis may be more likely to have an earlier period than usual, and those with PCOS may be more likely to have a later period than usual.

The graphs above show the proportion of women who reported the timing (blue bars) or flow (red bars) of their menstrual cycle by medical condition. It shows that those with endometriosis may be more likely to have an earlier period than usual, and those with PCOS may be more likely to have a later period than usual.

The results showed that among people on contraception, 42% said their periods were heavier than usual and 19% found it was lighter.

For comparison, for those who don’t use the devices, 32% said they were heavier and 14% said they were lighter. The difference was statistically significant.

Anthropologist says her period came soon after Moderna’s Covid jab

Anthropologist Dr Kate Clancy, from the United States, is one of many women who say they have had period problems after receiving the Covid vaccine.  She said that after receiving her first dose of Moderna, her period came a day earlier and was stronger than normal.

Anthropologist Dr Kate Clancy, from the United States, is one of many women who say they have had period problems after receiving the Covid vaccine. She said that after receiving her first dose of Moderna, her period came a day earlier and was stronger than normal.

Dr Kate Clancy, a medical anthropologist from Illinois, is one of many women who say they had period problems after receiving the Covid vaccine.

She said in February that after receiving her first dose of the Moderna vaccine, her period came a day earlier.

“I am on the third day of my period and still exchange extra long sanitary pads several times a day,” she wrote on Twitter.

“What is typical for me right now is maybe one or two regular pads (albeit extra absorbent, the ones from Always Infinity) for the whole day.”

The results also showed that patients with endometriosis – a disease in which the tissue lining the uterus grows in the ovaries – were much more likely to have an earlier-than-normal period compared to those who did. no disease.

And those with polycystic ovary syndrome (PCOS) – when the ovaries stop releasing eggs – were more likely to have a later period than others.

Dr Victoria Male, the immunologist who led the study, admitted that it was “difficult” to suggest a biological reason why women on contraception were more likely to have period problems.

She said the results may actually be due to women taking the pill monitoring their menstrual cycles more closely than others.

The pill can also trigger period changes.

Dr Male told MailOnline: “A lot of people who take hormonal contraception want to at least partially control their periods.

“They may be more likely to report the change because contraception normally makes their periods very regular – so this is particularly unusual for them.

‘The other possibility [that vaccines are changing periods] are we seeing a weak signal that some with PCOS may be more likely to have a late period.

The study – published as a pre-print on medRxiv – requested data from 1,273 women who kept a record of their menstrual cycle when they were vaccinated.

The group was between 29 and 39 years old.

The Pfizer vaccine was given to most participants (61 percent), followed by the AstraZeneca jab (27 percent) and the Moderna vaccine (10 percent).

Some 134 volunteers used hormonal contraception during the study, and 1,117 said they did not. The types of contraception deployed included the pill, implants, a patch, and a vaginal ring.

Some 87 participants suffered from PCOS and 60 from endometriosis.

Experts said the sample size was large enough to determine whether the vaccines affect the menstrual cycle.

But they added that larger studies in the United States would be able to observe rarer impacts vaccines have on menstruation, which their study was too small to detect.

Experts have already suggested that the immune response triggered by vaccines could also affect periods because the two systems are strongly linked.

Some pregnant women and those who wish to have a baby have been reluctant to come forward because of concerns about vaccines and fertility.

But experts insist the changes are transient in nature and there is no evidence that they are causing the problem.

Dr Male added: “Most women don’t seem to see an effect and most potentially vulnerable people should still get the jab because, in the short term, we know getting a Covid infection affects menstruation as well.

“In this study, some 36 women got pregnant out of the 2,000 involved, so that’s a lot.”

Separate studies have also been published in America to determine if Covid jabs could be the cause of changes in the menstrual cycle.

But they have also so far been unable to detect an impact on the periods that vaccines might have.

More than 41,000 menstrual changes have been reported by women to the country’s vaccine regulatory body after their inoculation.

The MHRA says it is reviewing the reports, but there is not yet strong evidence that these are certain side effects of the vaccine.


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