An emerging and complex health problem that remains poorly characterized and understood is long coronavirus disease 2019 (Long COVID). The rapid outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the ongoing coronavirus disease 2019 (COVID-19) pandemic.

Study: Association between vaccination status and reported incidence of post-acute COVID-19 symptoms in Israel: a cross-sectional study of patients infected between March 2020 and November 2021. Image Credit: Ralf Liebhold/Shutterstock

Long COVID is a post-infection condition in which individuals do not recover completely for several weeks or months after the acute episode. The effectiveness of COVID-19 vaccines against long-term symptoms of COVID19 is not well understood.

In a recent study published on the medRxiv* preprint server, scientists examined whether vaccination was associated with reporting long-term symptoms post-SARS-CoV-2 infection. Within the subgroup of individuals previously infected with SARS-CoV-2, researchers compared those who were vaccinated and those who were not in terms of self-reported long-term symptoms.

Long COVID and SARS-CoV-2 vaccination

The World Health Organization (WHO) defined long COVID as “A condition which occurs in individuals with a history of probable or confirmed SARS-CoV-2 infection, usually three months from the onset of COVID-19 with symptoms that last for at least two months and cannot be explained by an alternative diagnosis. Common symptoms include fatigue, shortness of breath, and cognitive dysfunction but also others involving the musculoskeletal, cardiac and central nervous systems, which generally have an impact on everyday functioning”.

Vaccination against SARS-CoV-2 is one of the most important interventions deployed to mitigate the pandemic. To date, over 58% of the global population has received at least one dose of the COVID-19 vaccines, accounting for 9.2 billion doses. In Israel, approximately 63.6% of the entire population have received a priming, two-dose course, and 45.6% have received a third dose. However, risk factors for developing long COVID have not been fully explored, and little is known about the impact of COVID-19 vaccination on long COVID.

A new study

The current study invited individuals at participating hospitals between March 2020-June 2021 to fill an online questionnaire. The participants had been PCR tested for COVID-19 infection. A total of 30,262 invitations were sent out. Two thousand three hundred forty-six individuals responded to the survey and agreed to participate. Of these, 951 individuals had tested positive for SARS-CoV-2, and these were the individuals who were included in the study.

The details sought included baseline demographics, details of their acute infection episode, the number of doses of the vaccine (and when administered), and information about symptoms they were currently experiencing. Some of the common symptoms were fatigue, headache, weakness in the arms of legs, persistent muscle pain, etc. Next, a binomial regression technique was used to contrast vaccinated and unvaccinated individuals regarding self-reported symptoms post-acute infection.

Main findings

Researchers observed that full vaccination (two or more vaccine doses) overall led to a significant fall in reporting the most common post-COVID-19 symptoms and an increase in full recovery. This was specifically more prominent in individuals aged above 60 years. The above result was not observed among individuals who received a single dose of the vaccine. About a third of the participants continued to report symptoms post-COVID-19. The fact that the associations were stronger for senior individuals was inconsistent with previous research. 

The vaccinated and unvaccinated groups were similar concerning sociodemographic characteristics, except for age. This is consistent with the COVID-19 vaccination strategy implemented by the Israeli Ministry of Health, which targeted the older population first. Some chronic conditions might have been present in the vaccinated (older) group, which were not considered in this study. However, scientists claimed that the results would get even stronger if these differences were considered because these conditions were more prevalent in the older, fully vaccinated group.

Concluding remarks

Long-COVID is a complex health problem that remains poorly characterized and understood. The current study provides novel insights into the effectiveness of COVID-19 vaccination on the long-term effects of SARS-CoV-2 infection. The main vaccine used in Israel was the one manufactured by Pfizer-BioNTech (BNT162b2 mRNA vaccine). The results reported in this study suggest that besides preventing severe disease and death, the vaccines (or at least BNT162b2) could play a vital role in mitigating long-term outcomes COVID-19, particularly among older individuals. 

More research is needed to objectively measure the long-term health outcomes in COVID-19 patients in a clinical setting. The authors of the current study are continuing to recruit participants and, in the future, hope to report with greater precision whether the Pfizer-BioNTech vaccine’s protective effect is sustained or not. The researchers will also consider the effects of different SARS-CoV-2 variants and vaccination on post-COVID symptoms in further research.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.