Women receiving Covid booster shots have reported symptoms similar to early signs of pregnancy.
Delayed or disrupted menstrual cycles, sore breasts and nausea are usual early signs of pregnancy, with some women reporting similar symptoms after receiving a Covid vaccine.
While these signs were not reported during clinical trials, they are becoming more common in women receiving a second vaccine, or booster shot.
Doctors said while a first menstrual cycle post vaccine could be disrupted, symptoms were short-lived and should not deter women from getting protected against coronavirus.
“It has been found some women experienced heavy flows or bleeding at an unexpected time in their menstrual cycle after taking the vaccines,” said Dr Zarqa Noreen Shah, an obstetrician and gynaecologist at Burjeel Specialty Hospital in Sharjah.
“Only a few women would experience this sort of reaction to the vaccines, with the majority not experiencing any changes to their menstrual cycle.
“For those who experience these signs, it doesn’t mean any harm to them. The vaccines are safe and it is just a temporary reaction of a body to the vaccine.
“It is usually a short-lived disruption to menstruation lasting only for a couple of cycles.”
It is not known if the symptoms are unique to a particular vaccine, or common to all types of Covid inoculations.
Thousands of people reported similar symptoms after taking a vaccine in the US, but researchers and gynaecologists have yet to establish a link between the vaccines and the reported changes.
Research led by Dr Kathryn Clancy, a human reproductive ecologist at the University of Illinois, asked vaccinated women about their symptoms after she experienced an unusually heavy period after her Covid jab.
More than 140,000 women reported similar disrupted menstrual cycles after taking a vaccine, via an online survey.
Doctors believe the reaction could be related to immunity.
Immune cells help in building up, maintaining and breaking down the lining of the uterus. When a person receives a vaccine shot, immune cells are activated.
These immunity changes could affect or influence menstruation, which might manifest as early menstruation, spotting, cramps and heavy bleeding.
“Menstrual cycles could be altered due to various reasons and can vary from one person to another,” said Dr Shah, who encouraged all women to continue their vaccination programmes.
“Stress could be another factor and can result in lighter or heavier periods.
“Just a few women who take the vaccine are likely to develop this kind of a reaction. And it has only been very brief.
“There are no long-term reactions or adverse effects. Vaccines are safe and are a must.
“People should outright reject other arguments that do not have scientific basis - it doesn’t cause loss of pregnancy or affect fertility.”
Both first and second doses of the Pfizer-BioNTech vaccines are the same, but each can trigger slightly different reactions in some people.
In a two-dose mRNA vaccine, some taking a second shot reported flu-like symptoms, nausea or a slight fever lasting a day or two due to their immune system ramping up.
After a first dose, the body’s defence is offered a key protein from the SARS-CoV-2 virus to enable it to develop a robust blockade against future infections.
Once it recognises the virus again when a second dose is administered, it triggers a similar response to the virus.
A more common sign associated with taking a vaccine is soreness around the injection site, usually the upper arm, but some women have reported painful breasts.
Doctors said women should not be concerned or confuse the feeling with breast cancer.
“Some women experienced pain at the injection site and after some hours, may feel pain in the axilla (an anatomical region under the shoulder joint where the arm connects to the shoulder),” said Dr Mohamed Khalafallah, a consultant in obstetrics and gynaecology at Bareen International Hospital in MBZ City, Abu Dhabi.
“This led some women to think that it may be breast cancer.
“It is important to understand that the enlarged lymph nodes are painful, while in breast cancer, it is without pain.
“If it is breast cancer, there are changes in the breast tissue, which is hormonal in nature and we can diagnose.
“Overall, the benefits of a Covid-19 vaccine far outweigh the temporary side effects.”