A new rapid review finds that full vaccination may reduce the odds of post-COVID-19 condition (PCC) by 27%, though more research is needed—especially in children and immunocompromised groups.

Study: Does COVID-19 vaccination reduce the risk and duration of post COVID-19 condition? Image Credit: KomootP/Shutterstock.com

A recent rapid review published by the European Center for Disease Prevention and Control (ECDC) explores the benefit of vaccination in avoiding or shortening adverse events following acute infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Introduction

The coronavirus disease 2019 (COVID-19) pandemic shook global healthcare systems, with hundreds of millions of cases and over seven million deaths over less than three years.

The rapid development and rollout of the nucleic acid vaccine against this virus led to a marked reduction in the risk of severe illness and death following infection while allowing economies and social institutions to reopen.

However, millions of cases of long Covid have been reported following acute, often asymptomatic, SARS-CoV-2 infection. This term refers to symptoms of new onset or persisting after the acute infection, irrespective of disease severity or duration of illness, and may last for weeks, months, or years.

These may include brain fog, fatigue, or breathlessness, typically affecting daily life. They occur within three months of the infection and last for two or more months.

Long Covid has been variously described based on the symptom criteria, the duration of symptoms, and the delay from infection to the appearance of symptoms. This hinders direct comparison between studies.

To overcome this hurdle, the World Health Organization (WHO) released a clinical definition for various forms of long-term COVID-19, clubbing them together as ‘post-COVID-19 condition (PCC)” in 2020.

About the review

The current study sought to quantify whether COVID-19 vaccination reduced the risk, duration, or both of PCC. It used rapid review methodology, using comparable studies published after October 2021.

All studies were based on vaccines authorized by the European Medicines Agency (EMA). The researchers compared fully vaccinated people with unvaccinated individuals.

The review included 12 studies. Most of the studies explored the risk of PCC in adults, while two looked at the risk in immunocompromised adults. One study examined the risk in children or adolescents.

Of the adult general and immunocompromised studies, one each, along with the child/adolescent study, was considered likely to be biased.

These studies failed to adjust for confounding factors, did not mention loss to follow-up, or had inadequate sample sizes. Several studies did not report the time lag from vaccination to SARS-CoV-2 infection. 

Risk of PCC

The results reflected a reduced risk of PCC in the fully vaccinated group vs the unvaccinated group. The participants in the six low-bias studies in general adult patients were recruited both from the community and from hospitals over different periods during the pandemic. Thus, the infecting strains were likely to be diverse, as well as the severity of the disease.

For the low-bias immunocompromised adult study, comprising adults living with human immunodeficiency virus (HIV), vaccination was not associated with an observable protection against PCC.

Comparable studies were then pooled, and a meta-analysis was carried out on general adult participants.

This included four studies with a low risk of bias. The pooled analysis suggested a 27% reduction in the odds of PCC with full COVID-19 vaccination compared to no vaccination.

Duration of PCC

None of the studies included longitudinal follow-up of PCC symptoms. A single adult study including hospitalized participants classified PCC as either major physical symptoms (MPS) or major neuropsychological symptoms (MNS).

MPS included the presence of two or more of the following symptoms: fatigue, fever, cough, or breathlessness. MNS included anxiety or depression, brain fog, and brain fade.

Symptoms were asked for at 12 and 18 months from hospital discharge. The results showed that MPS might be reduced in duration following vaccination, but not MNS. However, these findings are based on a very small sample and need to be carefully verified.

Conclusions

The study’s results indicate that vaccination may be protective against PCC, reducing but not eliminating its risk following SARS-CoV-2 infection.

This agrees with earlier studies and indicates that vaccination not only protects against severe outcomes of acute COVID-19 but may reduce the risk of PCC in adults.

A similar statement cannot be made about children and adolescents or immunocompromised adults because of the inadequate samples available.

The impact of COVID-19 vaccination on PCC duration could not be assessed due to the lack of proper studies in this area. “This review highlights the ongoing need for further studies evaluating PCC that consistently apply the WHO case definitions.”