A recent case-control study in South Africa reveals that regular physical activity improves the effectiveness of the vaccine against Covid-19. While the positive impact of regular physical activity against severe Covid-19 outcomes is well understood, the association between regular physical activity and vaccine efficacy is underexplored.
The study primarily used physical activity data from 196,444 participants and concluded that increased levels of regular physical activity enhanced the protective effects of vaccination against Covid-19 hospitalization and exhibited a dose- answer.
The researchers conducted a negative case-control study and a retrospective analysis using data collected by Discovery Health and Vitality. A negative case-control is commonly used to assess the effectiveness of the annual influenza vaccine; the studies would calculate the odds ratio of a positive test when vaccinated against specific pathogens and a negative test when vaccinated against a specific pathogen. In this case, the researchers were interested in estimating hospital admission for Covid-19 among those who are vaccinated and unvaccinated based on their “regular” levels of physical activity.
Colley et al. used anonymized data from Discovery Health and Vitality and derived information from members who had a partnership from mid-February to the end of October 2021. Participants were at least eighteen years old and were categorized into one of three levels of physical activity according to their average monthly physical point allocation two years before the study: light activity (less than 60 minutes of at least moderate intensity activity per week), moderate activity (those who practice 60 and 149 minutes of activity of at least moderate intensity per week) and vigorous activity (people engaged in at least 150 minutes of at least moderate activity per week). To qualify for the study, participants had to submit proof of Covid-19 infection at the start of the study, given that they had tested positive up to 3 months previously.
Vaccinated participants were healthcare professionals who were vaccinated following a separate study. The unvaccinated participants were a mix of health and non-health professionals who are members of Discovery Health and Vitality. Using stratified random sampling, roughly proportional ratios of unvaccinated to fully vaccinated participants within each physical activity group. There was a slight difference in biological sex between the three groups: 64.1% of the low activity group were female, compared to 56.4% and 50.9% of the moderate and high intensity physical activity groups . Participants in the moderate and high activity groups also had slightly higher Covid-19 risk factors on average compared to the low action group.
Collie et al conducted three sensitivity analyzes to investigate vaccine effectiveness among and within the three groups in relation to their physical activity levels. In the first sensitivity analysis performed, the effectiveness of the vaccine among fully vaccinated participants in each group compared to the general population. No statistical difference was found, suggesting that the sample was representative of the population.
Collie et al performed a unique multinomial Poisson regression model, which estimates the relative risk of hospitalization given the level of physical activity. Compared to unvaccinated individuals with low physical activity, vaccine efficacy was 91.5% for vaccinated individuals with high physical activity. Additionally, using unvaccinated individuals with low physical activity as a baseline, there was a difference in vaccine efficacy between vaccinated individuals in high-intensity physical activity and vaccinated individuals in exercise. moderate intensity of about 28.1%. This sensitivity measure also found the difference between hospitalization vaccine effectiveness between those who were vaccinated at least 28 days before the study with low physical activity and those who were vaccinated at least 28 days before the study. with high physical activity at 25.8%, consistent with the findings of the main study.
In a third sensitivity analysis, Collie et al used Bayesian modeling, allowing testing of hypothetical causal relationships between vaccine efficacy and physical activity levels. This analysis determined a 25% difference in vaccine effectiveness between vaccinated participants performing high-intensity physical activity and vaccinated participants performing moderate-intensity physical activity, compared to unvaccinated participants performing low-intensity physical activity. It also showed that the main difference was 25.8%, which confirms the results of the multinomial positional regression analysis and the results of the main study.
Collie et al found that vaccine efficacy and physical activity appear to have a dose-response relationship, where increased regular physical activity improves vaccine efficacy against Covid-19 hospitalization. Among fully immunized people, the vaccine was most effective among those with high activity levels (85.8%), which was significantly higher than those with low physical activity (60%). The 25.8% difference was supported by both sensitivity analyses, and these results further validate the World Health Organization’s recommendation of regular physical activity (150-300 minutes of moderate-to-vigorous activity per week), as it can have significant health benefits, such as preventing serious illness.
Collie et al’s findings align with existing literature focusing on increased vaccine effectiveness with regular physical activity. One study measured antibody levels in 898 patients with autoimmune rheumatic disease about two months after being fully vaccinated with the CoronaVac vaccine. After adjusting for covariates, active patients had higher antibodies and geometric mean titers (GMTs) than their counterparts with sedimentary or very low physical activity. The researchers also noticed a dose-response relationship between physical activity and the presence of Covid-19 antibodies and GMT: patients performing at least 350 minutes of physical activity per week had more Covid-19 antibodies and a higher GMT compared to the least active group exercising no more than 30 minutes per week. This study suggested that a lifestyle incorporating greater physical activity may help protect immunocompromised communities by improving the immunogenicity of the Covid vaccine. In a separate study, physical activity was associated with an increased presence of antibodies up to 6 months after vaccination in immunocompromised patients. Through logistic regression analysis, higher rates of seroconversion and neutralizing antibodies were found in patients with higher levels of regular physical activity.
Although Collie et al encourage increased regular activity to maximize protection from the Covid-19 vaccine, it is important to recognize that the study is not without limitations. This study was carried out before the emergence of Omicron. Additionally, the sample participants are likely to have a higher socio-economic status, which is an inadequate representation of the entire population of South Africa. A healthier diet and better sleep habits may also contribute to greater vaccine effectiveness in highly active participants compared to their low-activity counterparts. Finally, the biological mechanism behind the vaccine’s efficacy and physical activity remains unclear, largely due to the lack of immunogenicity and cell-mediated response analyzes in the study. Further studies are needed to validate the main results of the study.