Jerusalem, Feb 14 (IANS): The proportion of women who reported side-effects after receiving their first, second or third dose of the Pfizer vaccination is almost twice (1.9 times) than among men.

The Pfizer vaccines are based on the injection of a nucleic acid (mRNA) that codes one of the proteins of the virus. The goal is to stimulate production of antibodies against the virus and to protect the recipient against the disease.

The vaccination is sometimes accompanied by side-effects, manifested, for example, in pain at the vaccination point or in the entire arm, fever, weakness, fatigue, and paresthesia in various parts of the body.

"We don't know what mechanism is involved, but it may be related to differences between the sexes in the immune system or in the perception of the side-effects," said Manfred Green, from the School of Public Health at the University of Haifa in Israel.

"One possibility is that immune system in women responds more strongly than in men to foreign antigens," he added.

In the study, published in the journal Vaccines, the team examined the differences between men and women in the reporting of side-effects after receiving the Pfizer vaccinations in Israel.

The study was based on the collection of data from four different sources -- reports forwarded to the Ministry of Health concerning side-effects in individuals above the age of 16 during the period December 2019 through June 2021; a survey of 923 participants over the age of 30 conducted in June 2021; and two additional surveys with 560 participants aged 20-65 conducted in places of work in September 2021.

The results showed that the proportion of women reporting pain in the entire arm after receiving the vaccination was 7 times higher than men following the first vaccination, 4.2 times higher following the second; and 4.1 times more after the third jab.

The proportion of women who reported weakness was 30 times higher than men after the first dose, 2.6 times higher after the second dose, and 1.6 times higher after the third dose.

Women suffered from headaches 9 times higher than among men after the first dose, 3.2 times higher after the second dose, and 2.45 times higher after the third dose.

The study emphasises the need to report vaccine side-effects disaggregated by gender.

Meanwhile, the European Medicines Agency's safety committee is looking into reports of problems with women's menstruation tied to the use of mRNA-based Pfizer and Moderna's Covid vaccines.

Its safety committee is investigating both cases of heavy bleeding, as well as missed periods.