A British study assessing whether Covid vaccines can disrupt periods may not find anything because it is too small, scientists say.
Reproductive experts based at Imperial College London are currently monitoring the menstrual cycles of 250 women before and after inoculation.
But lead researcher Dr Victoria Male said the tiny number of participants means the study won’t pick up a potential link unless it is ‘really common’ — affecting more than one in ten women.
To prove a link, scientists need to untangle normal period changes from those which may have been sparked by inoculations.
But because period issues, which are often transient, affect approximately one in ten women every year, thorough investigations are needed to spot whether the jab may really be to blame.
Nearly 36,000 women have reported experiencing period issues after receiving the Covid vaccine. But experts fear this is only the tip of the iceberg because many women who experienced the changes likely did not report them.
Period issues reported after getting the Covid vaccine include heavy bleeding, missing periods, and periods being earlier or later than usual.
Some postmenopausal women have also said they experienced vaginal bleeding after being vaccinated.
Dr Male said they aimed to establish whether there was a link and, if there is, get this listed as a side effect of Covid vaccines to allay any concerns over being jabbed.
She said that by ‘brushing it under the rug’ regulators were not acknowledging fears over jabs.
Some 35,700 women have now come forward to say their periods were disrupted after getting a Covid vaccine, it was revealed (stock image)
Experts only honed in on a connection between the AstraZeneca vaccine and blood clots after noticing more cases than expected among recipients.
And the same happened for Pfizer’s jab when it was linked to heart inflammation, or myocarditis.
But both issues were spotted in data collected from real-world roll outs because the complications were rare enough to disentangle the link.
Britain’s medical regulator has refused to accept or deny a link to disrupted cycles, and says most menstrual problems appear to be ‘transient’ in nature.
But period issues have previously been linked to other vaccines, such as the HPV jab.
However, there is no evidence that Covid vaccines affect fertility, top doctors insist.
Women asked to report periods after getting the Covid vaccine
Dr Victoria Male has asked women to report their menstrual cycles before and after they were vaccinated against Covid.
She is looking for women who regularly keep track of their periods to participate in the study.
For the study, they will need to submit data on their menstrual cycle and when their Covid vaccinations took place.
To take part in the study, click here.
Britons are encouraged to report any suspected side effects of the Covid vaccines to Britain’s medical regulator’s yellow card system.
This can be accessed here.
Dr Male told MailOnline the first batch of data is expected by the end of September, with the study to be published later in the year.
She said: ‘If we don’t find anything, all we can conclude is if there is a link between periods and vaccines it is less common than the stdy can pick up.’
Dr Male said she was only able to recruit 250 women for her study because when she started looking for participants most had already been inoculated.
The participants come from countries including the UK and Australia and have either already received one dose or not been vaccinated.
They are all asked to record at least three menstrual cycles and note down how they changed, if at all, after being vaccinated compared to normal.
In a second arm of the study, which has already received more than 1,800 responses, women who normally track their periods are asked to report whether they changed after Covid vaccination.
Dr Male said women who did experience changes are far more likely to report to this arm of the study those than those who did not, which may skew the figures.
She is running the study in her spare time because there is no money available for trials investigating how vaccines may affect periods in the UK.
Explaining why the trials are needed, she said: ‘There is an argument that well if it quickly go away and do not do permanent harm, why bother studying it? Definitely people have made that point.
‘There are two reasons. The first is that a lot of people are concerned about this and they are particularly concerned because of this misinformation around fertility.
‘I think that by saying this is not something important enough to look into we are not allaying fears. By brushing it under the rug we are not acknowledging these worries.
‘The other reason is a lot of people rely on knowing when they are ovulating. If your period does come on early that is a horrible mess that you have to clean up.
‘We want to be able to say that this month you might want to be sure that you have a tampon in your purse, for example.’
She added the aim is to establish whether there is a link between Covid vaccines and period changes, and then list this as a side-effect to allay concerns.
‘Imagine if you went and got your vaccine and the next day you got a fever,’ she said. ‘You might reasonably go “oh my god I don’t know what is wrong with me” if that was not listed as a possible side effect.
‘We would like to be able to do the same thing with periods. Say, for example, five per cent of women may get a late period after being vaccinated.’
In the US authorities have pumped $1.6million (£1.1million) into four studies looking into whether Covid vaccines could trigger period issues.
They are involving thousands of women, with results expected to be published ‘before the winter’ this year.
Other countries — including the UK — will use this to help decide whether period issues should be listed as potential side effects of the vaccines.
Evidence that Covid vaccines may be triggering changes to menstrual cycles is ‘purely anecdotal’ at present. There is no clear sign whether there is a difference in changes after the first and second doses.
Covid itself — like other diseases such as HIV — is also known to trigger period issues.
Scientists have said it is possible the vaccines could be behind period problems because the immune system is involved in the menstrual cycle.
Many factors including stress and minor illness can trigger period issues. Some women also often have irregular cycles.
Dr Alison Cave, from the Medicines and Healthcare products Regulatory Agency, said: ‘We are closely monitoring reports of suspected menstrual disorders following Covid vaccination.
‘Based on our current rigorous safety monitoring, women can be reassured that the current evidence does not show a link with any changes in women’s periods or symptoms, nor is there any evidence to suggest that Covid vaccines will affect fertility.
‘This is also the conclusion of our expert scientific advisory committee, the Commission on Human Medicines.
‘While uncomfortable or distressing, period problems are extremely common and stressful life events can disrupt women’s periods. Changes to the menstrual cycle have also been reported following infection with Covid and in women affected by long-Covid.
‘Our advice remains that the benefits of vaccination outweigh the risks for most people.’
More than 85 per cent of women aged between 18 and 55 in Britain have already received at least one dose of a Covid vaccine.