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Introduction
In March 2020, the world was faced with the declaration of a global pandemic - covid-19. By June, the world had just over 767 million cases reported to the WHO. Vaccines against the disease were rapidly developed and the first dose in Sweden was administered less than a year after the pandemic began. The effectiveness of the COVID-19 vaccination against the various strains of COVID-19 is shown in this Swedish study. Soon after the pandemic started, even people who recovered from the infection had persistent symptoms. This was called post-COVID-19 condition (PCC) or long COVID. 2% of adults with COVID-19 in Sweden had PCC, but these diagnoses were based on self-reported systems, so there may have been a higher incidence rate than known. Symptoms of PCC include fatigue, cognitive impairment, headache, muscle pain, chest pain and palpitations. There are four types of PCC; chronic fatigue-like syndrome, respiratory syndrome, chronic pain syndrome and neurosensorial syndrome (a decrease in sensitivity in the nervous system). PCC occurs in individuals who had a history of a specific strain of COVID-19, SARS-CoV-2 infection, three months after the onset of COVID-19 with symptoms that lasted over two months. There is little information to ascertain how effective the COVID-19 vaccines are against PCC. This study investigates the effectiveness of the primary COVID-19 vaccine (first two doses and the booster dose within the recommended time frame) against PCC.
Summary
The study was a Swedish study, and participants were over the age of 18. Individuals were followed from their first infection of COVID-19 until either emigration, vaccination, reinfection or until they passed away. The primary outcome was a clinical diagnosis of PCC, which had to be 28 days after the first COVID-19 diagnosis. The researchers obtained information on age, sex, education level, employment status and other required knowledge from the Swedish database for health insurance.
Conclusion
The researchers found that there was a strong association between vaccination before the first diagnosis of COVID-19 in patients and a reduced risk of diagnosed PCC. Unvaccinated individuals had almost four times the PCC diagnoses as compared to those who had vaccines before they were infected. There was a 58% effectiveness of the vaccine against PCC, and the effectiveness increased with each dose. The strengths of this study were the large sample size, the fact that the researchers used high-quality databases to obtain information on the patients, and that it was mandatory for each vaccine dose to be registered in the national vaccination register. This means that the exposure data was accurately measured. Secondly, the researchers had access to previous health data of each individual, which strengthened their study. However, there were some limitations to this study as well. The first is that the PCC may have been overdiagnosed or underdiagnosed, which means that there were more or fewer diagnoses than actual occurrences of the condition. This is because the condition was fairly new, and its manifestations were not yet clear to healthcare workers. Additionally, it is possible that the effectiveness of the vaccine differs in patients who experience different symptoms of PCC within a given spectrum. In conclusion, this study highlights the importance of being vaccinated against COVID-19 in order to reduce the likelihood and severity of PCC in the future.
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