Large UK study underpins role of COVID-19 vax in mental illness

In a cohort study of over 18 million individuals with up to 2 years of follow-up, the incidences of most mental illnesses were markedly elevated following COVID-19 diagnosis compared with before or without COVID-19, particularly among the unvaccinated and before COVID-19 vaccines became available.

The study was conducted in three cohorts: one before vaccine availability, followed during the wild-type/Alpha variant eras (January 2020 through June 2021), and two during the Delta variant era (June through December 2021). [JAMA Psychiatry 2024;doi:10.1001/jamapsychiatry.2024.2339]

The pre-vaccine availability cohort included 18,648,606 individuals (median age 49 years, 50.2 percent women), the vaccinated cohort had 14,035,286 participants (median age 53 years, 52.1 percent women), while the unvaccinated group included 3,242,215 individuals (median age 35 years, 57.9 percent men). The incidences of COVID-19 infection in the respective cohorts were 1,012,335, 866,469, and 149,745.

Depression was the most common mental illness, with 1,329,270, 352,944, and 57,810 diagnoses in the pre-vaccine availability, vaccinated, and unvaccinated cohorts, respectively. The corresponding diagnoses of serious mental illness in these cohorts were 397,368, 88,500, and 18,726.

In each cohort, day 0 saw tremendously high incidences of all outcomes. During the rest of week 1 through week 4 after COVID-19, the rates of most outcomes were higher than before or without COVID-19.

During weeks 1–4 after COVID-19, the adjusted hazard ratios (HRs) for depression and serious mental illness among the vaccinated were 1.16 and 0.91, respectively. The corresponding adjusted HRs were higher in the unvaccinated (1.79 and 1.45) and pre-vaccine availability cohorts (1.93 and 1.49).

“[The] attenuation of adverse effects of COVID-19 on mental illnesses in the vaccinated may be explained by reduced disease severity due to vaccination,” the researchers explained. “Potential mechanisms include reduced systemic inflammation and psychological benefits of vaccination, such as reduced concern about COVID-19 and increased social engagement.”

On the other hand, the higher incidence of mental illnesses in the pre-vaccine availability cohort may reflect the greater uncertainty and public concerns around COVID-19 outcomes and the efficacy of treatment during the start of the pandemic, they added.

Vaccination remains crucial

The effects of vaccination in preventing and reducing the severity of COVID-19 are well established, but data on its effects on other adverse COVID-19 outcomes, including mental illnesses, is lacking. [Infect Drug Resist 2021;14:3459-3476; BMJ 2022;377:e069317]

“[Our study shows that] the incidence of mental illnesses was elevated for up to a year following severe COVID-19 in unvaccinated people. These findings suggest that vaccination may mitigate the adverse effects of COVID-19 on mental health,” the researchers said.

Of note, the likelihood of having mental illnesses recorded may be higher among individuals with COVID-19, particularly those who have been hospitalized, given their greater contact with health services. This may not be the case for unvaccinated individuals, who may have had fewer health service visits and testing for COVID-19 infection, hence the potential for underestimated effects.

Nonetheless, the findings underline the importance of COVID-19 vaccination in the general population, specifically among those with mental illness who may be at higher risk of adverse outcomes following COVID-19. [Br J Gen Pract 2021;72:e51-e62; World Psychiatry 2022;21:153-154; Mol Psychiatry 2022;27:1248-1255]

“Our findings highlight the wider public health benefits of vaccination. Prior mental illness may influence vaccine uptake, highlighting the importance of actively encouraging vaccination of people with mental health difficulties,” they said.