Several reports show women are experiencing stronger side effects to the vaccine than men and it isn't unique to COVID-19.
“This has been observed time and time again,” said Dr. Monica Gandhi, an infectious disease expert and professor of medicine at the University of California San Francisco. “Serologic responses in women to hepatitis B vaccine, to hepatitis A vaccine, to measles vaccines are more prominent in women than men. So, this has been totally seen.”
Dr. Gandhi says because women have a stronger immune response to vaccines, it also means they're more likely to clear viral infections through their own immune systems. That can help explain why we've seen more severe cases of COVID-19 in men.
Dr. Gandhi says part of it comes down to the different hormones men and women produce. Estrogen and progesterone, for example, stimulate cell-mediated immunity. That's the body's own response that doesn't use antibodies.
“I think hepatitis C is the classic example,” said Dr. Gandhi. “Many people are exposed to hepatitis C, but our immune system determines the eventual course of hepatitis C, because we can clear it, or we cannot clear it, and that can go on to become chronic and women are just much more likely to clear hepatitis C infection.”
Dr. Gandhi says it would be useful for vaccine trial data to be split up by gender. She adds this would be valuable information for COVID-19 vaccine-makers moving forward.
Research published in JAMA and the Lancet Medical Journal also talk about how people who have recovered from COVID-19 are generating more antibodies from just one dose of the vaccine than someone who has never had COVID-19. That's regardless of gender.
But until we know more, Dr. Gandhi says everyone should stick to the recommended two doses of the COVID-19 vaccine.