Young women more susceptible to 'long COVID,' vaccinations effective: Japan, int'l study

A patient suffering from COVID aftereffects, or “long COVID,” sees a doctor in Osaka’s Kita Ward in April 2022. (Mainichi/Maiko Umeda)

TOKYO — Research within and beyond Japan is bringing into focus several key points of COVID-19 aftereffects, including that young women are particularly susceptible and vaccines are an effective tool for prevention.

The World Health Organization (WHO) defines post-COVID condition, or “long COVID,” as symptoms that appear three months after infection and persist for at least two months.

A study by Yokohama City University Hospital, published in February 2023, analyzed data on 74,690 people from countries including Norway, Switzerland, Japan and the United States. Of patients infected with the omicron variant, as many as 11% experienced long COVID.

Given a checklist of symptoms, 50% of long COVID patients felt groggy and 41% felt muddled thinking or “brain fog.” Other symptoms included headaches (29%), memory loss (28%), an impaired sense of smell (26%) and depression (23%).

The tendency for women to be likely to develop symptoms came to light in a study by the University of Washington researchers published in the October 2022 Journal of the American Medical Association. Their analysis of 1.2 million patients from 22 countries including the U.S., Germany and Italy found that many women in their 20s to 40s experienced long COVID. Both men and women were more likely to show symptoms in their 20s.

How long do the aftereffects persist? According to a paper published in The BMJ (formerly the British Medical Journal) in 2023, 28.9% of patients still had symptoms after six months, falling to 20.3% after one year. Because 18.1% did not recover even after two years, the research team concluded that if symptoms persist more than six months, they will continue for two years in a majority of cases.

The mechanisms behind long COVID are gradually becoming clear. According to a preprint paper published by researchers at Harvard University in October of last year, a wide range of neurological disorders had developed in the brains of 12 people with post-COVID conditions compared to 43 healthy individuals. Inflammation is thought to be the cause.

Another paper points to persistent infection and reactivation of the virus that remains in the body as a cause of inflammation. The infection is also said to trigger abnormalities in the immune system that make it attack the body.

Many studies report vaccinations as an effective way to prevent long COVID.

In a study of mice published in a sister publication to the English journal Nature, vaccinations suppressed brain inflammation. Since the effect persisted even after reinfection, inoculation is thought to protect against post-COVID.

Vaccines’ effectiveness at preventing long COVID was detailed by researchers at Sweden’s University of Gothenburg in the BMJ. Compared to the unvaccinated, those who had received a shot had a 21% lower incidence of symptoms, improving to 59% for those with two doses and about 73% with three or more.

Gifu University’s professor Takayoshi Shimohata emphasized, “I want more people to know that vaccination is more effective in controlling aftereffects than imagined.”

Aichi Medical University professor Takahiro Ushida, a member of the editorial board for the country’s COVID-19 guidelines, explained, “It is often difficult to see clear differences in blood samples and other data, making the choice of treatment tricky for patients with post-COVID symptoms. These signs are diverse and fundamental treatments have not been established.” He added, “To return to their jobs and social activities while experiencing the aftereffects, patients need shorter working hours and support from industrial physicians. Inability to return to society could lead to a vicious circle of further worsening symptoms.”

(Japanese original by Ryo Watanabe, Lifestyle, Science & Environment News Department)