Israeli scientists have discovered that the proportion of women who reported side effects after receiving their first, second, or third dose of the Pfizer vaccination is almost twice as much as men.
The findings were uncovered by researchers from the School of Public Health at the University of Haifa and published in the journal Vaccines.
The researchers examined the differences between men and women in the reporting of side effects after receiving the Pfizer vaccinations in Israel. Women were found to have 1.9 times as many side effects as men, according to the study.
“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 the immune system in women responds more strongly than in men to foreign antigens,” commented Prof. Manfred Green, the study’s principal investigator.
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 the production of antibodies against the virus and to protect the recipient against disease. The vaccination is sometimes accompanied by side effects that are manifested in pain at the vaccination point or in the entire arm, or through fever, weakness, fatigue, and paresthesia in various parts of the body.
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.
While the results showed that reporting side effects following three vaccinations were higher among women than among men, it also showed the highest frequencies of side effects were reported among participants following the second vaccination.
Side effects were generally mild, according to the study.
An analysis of the findings shows that the proportion of women reporting pain in the entire arm after receiving the vaccination was seven 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 nine 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.
This isn’t the first time it has been reported that women have more side effects than men from a COVID-19 vaccine. In April, USA Today reported that among nearly 7,000 reports processed through the Centers for Disease Control and Prevention’s Vaccine Adverse Event Reporting System from December 14 to January 13, more than 79 percent of them came from women. The most frequently reported side effects were headache, fatigue, and dizziness.
Women were also more likely to experience some of the vaccine’s more unusual side effects, such as an itchy red rash at the injection site. Women accounted for 77 percent of the Moderna vaccine’s reported side effects.
Why do women exhibit more side effects to vaccines than men? The USA Today article chalked it up to a great immune response to vaccines.
“From a biological perspective, women and girls produce sometimes twice as many infection-fighting antibodies from vaccines,” said Rosemary Morgan, a research scientist at Johns Hopkins Bloomberg School of Public Health.
“I am not at all surprised,” said Sabra Klein, a microbiologist, and immunologist at the Johns Hopkins Bloomberg School of Public Health, told The New York Times three months later. “This sex difference is completely consistent with past reports of other vaccines.”
Last year, The Ministry of Health (MOH) released information on side effects recorded close to coronavirus vaccinations in Israel. At the time, 3.1 million people in Israel received the first dose of the vaccine, and 1.87 million received both doses. The side effects that appeared were more or less as expected from the clinical trials by Pfizer, maker of the vaccine that most Israelis who have been vaccinated have received. The side effects were mostly been light and transient, but there have also been some more severe cases, Globes reported. Side effects were more common among young people, and slightly more common among women than among men, MOH said.