A study from international vaccine alliance organisation Gavi has suggested that Covid-19 antibodies reduce faster in men than women
Medical research historically has often taken a one-size-fits-all approach, lumping women and men together despite growing evidence that the sexes differ in how they catch and fight disease. Covid-19 seems to be a case in point, with women more likely to be infected but men thought to be up to twice as likely to die from the virus, the study found.
The study, which has not yet been peer-reviewed, tracked for nearly six months 308 members of staff at Strasbourg University hospitals in France who had a confirmed Covid-positive test. Most of the recruited patients had mild disease.
Different antibodies were measured using three different tests at two points over a 172-day period. At the first blood sampling, men older than 50 and those with a body mass index (BMI) of more than 25 exhibited the highest antibody levels.
At the second sampling, levels of antibodies - including neutralising proteins designed to thwart the virus from latching on to human cells, had fallen further in men than in women, regardless of age and BMI, the researchers said.
"Other studies have shown that men have a higher antibody response than women in the acute phase – but we're showing that even though men have a higher response in the beginning, their fall in antibody levels is much quicker over time, while women seem to have more stable levels," said Samira Fafi-Kremer, head of virology at Strasbourg University hospitals and one of the authors of the study.
"I call this the new manifestation of girl power," she joked.
Olivier Schwartz, another of the authors and the head of the Pasteur Institute's virus and immunity unit, said the decline appeared to depend on how high antibody levels reached to begin with.
"So if you have more antibodies, you will have a more rapid decline, but we don't know exactly why," he said.
Dr Sabra Klein, a co-director of the Johns Hopkins Center for women's health, sex, and gender research, said vaccine developers should analyse data to compare male and female responses over time because it was likely that the male-biased decline in antibodies would occur following vaccination as well.
"If functional antibody responses decline to a greater degree in males than females following vaccination, then it may be that males need another booster vaccine to maintain immunity," she said.
Understanding of coronavirus immunity is far from complete. Scientists have cautioned that while antibodies – generated by B-cells – are key to the human defensive arsenal, they are not the only weapons deployed by the immune system. T-cells, which are tasked with stimulating B-cell production as well as annihilating respiratory cells the virus has inhabited, are equally crucial.
"I am not surprised that there might be differences in the intensity of the immune response, as this is in line with other infections, but … we need more research," said Dr Sabine Oertelt-Prigione, chair of sex and gender-sensitive medicine at Radboud University in the Netherlands.
"It is likely that memory T-cells might be preserved after infection (or vaccination) and be able to support an immune response in case of a secondary infection, as is the case in many other viral infections, but we have no proof of this yet."
In November, an 100-patient study led by the UK coronavirus immunology consortium found that T-cell immunity is likely to be present within most adults six months after primary infection.
A separate 185-patient study, which is yet to be peer-reviewed, has shown that at eight months after infection, most people who have recovered still have enough immune cells to prevent disease.