Proportion of women reporting side-effects after the 1st, 2nd or 3rd dose of the Pfizer vaccination almost twice (1.9 times) that among men

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) that among men. This finding emerges from a new study undertaken in the School of Public Health at the University of Haifa and published in the journal Vaccines. “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. One possibility is that immune system in women responds more strongly than in men to foreign antigens,” commented Prof. Manfred Green, the principal investigator of the study.

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 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. The researchers 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 of the study show that reporting of side-effects following the first, second, and third vaccination is about 1.9 times higher among women than among men. The highest frequencies of side-effects reported among all the participants were those following the second vaccination. The side-effects were generally mild, including pain at the vaccination point, fever, headaches, weakness, and paresthesia in the arm.

An analysis of the findings shows that the proportion of women reporting pain in the entire arm after receiving the vaccination was 7 times higher than among men following the first vaccination and 4.2 times higher than among men following the second vaccination; the proportion of women suffering from this side-effect after the third vaccination was 4.1 times higher than among men. 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. The proportion of women suffering from headaches was 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 results of the study emphasize the need to report vaccine side-effects disaggregated by gender.

The current study was undertaken by Prof. Green of the School of Public Health at the University of Haifa together with Dr. Dorit Nitzan, emergency director of the European Region of the World Health Organization; Dr. Rania Abdullah and Dr. Victoria Peer of the School of Public Health at the University of Haifa; Dr. Avi Magid of the Jezreel Valley College; Dr. Neta Hagani of Rambam Hospital; and Prof. Emilia Anis of the Ministry of Health.