CME INDIA Presentation by Dr. Rajeev Jayadevan, MD DNB MRCP ABIM (Med/GE) Co-Chairman National IMA COVID Task Force.

Does Exercise Improve the Effect of Vaccines? Probably Not. Here is Why?

Conclusion from a recent study

Association between regular physical activity and the protective effect of vaccination against SARS-CoV-2 in a South African case–control study

  • “Regular physical activity was associated with improved vaccine effectiveness against COVID-19 hospitalisation, with higher levels of physical activity associated with greater vaccine effectiveness. Physical activity enhances vaccine effectiveness against severe COVID-19 outcomes and should be encouraged by greater public health messaging.”(Ref.2)
It is already known
Regular physical activity has protective effects against severe COVID-19 outcomes (such as hospital admission, intensive care unit admission, ventilation and death).
Previous studies have shown associations between physical activity levels and antibody levels in response to COVID-19 vaccines.
This study tells now
Objectively measured regular physical activity is associated with enhanced effectiveness of vaccination with Ad26.COV2.S against COVID19-related hospital admission and a possible dose–response is demonstrated.
Pondering what this study points
Public health messaging should encourage physical activity as a simple, cost-effective way of enhancing vaccine effectiveness to mitigate the risk of severe COVID-19 illness requiring hospital admission.
  • A recent study from South Africa published in the BMJ claimed that regular physical activity was “associated with greater vaccine effectiveness”. The authors go on to say that physical activity “should be encouraged as a simple cost-effective way of enhancing vaccine effectiveness”. This study has been widely quoted.
  • While there is no doubt that physical activity is a good thing, I do not believe this is a correct conclusion.
  • But why did those who did more exercise have less hospitalisation? Is it really because exercise “strengthened the immune response to vaccine?”
Does Exercise Improve the Effect of Vaccines? Probably Not. Here is Why?

Vaccine effectiveness across physical activity subgroups 28 or more days since vaccination. Credit: Collie S, et al. Br J Sports Med 2022;0:1–7. doi:10.1136/bjsports-2022-105734

Lesson: Correlation is not causation

  • In research we often find two factors occur together (association/correlation). But that doesn’t mean one caused the other.

There is a hidden variable involved here: it is called FRAILTY.

  • The most likely explanation is as follows.
  • Those who did less exercise were unable to do so because they were more frail. And that is independent of having “known diseases” like heart failure, diabetes or obesity, which were evenly matched between the high and low exercise groups.
  • To quote a common example I use in this context, if we find a Rolex watch on a person‘s wrist, there’s a good chance that this person is rich when compared to a person wearing a cheap watch. But if any random person goes and buys a Rolex watch, that does not make him a rich person.
  • In other words, the Rolex is a sign of (is associated/correlated with) being rich, but it is not the cause (or reason) of being rich.
  • Let’s look at people who do regular exercise with those who do not exercise, all other parameters like age being the same.
  • Exercising is a feature of robust, healthy, non-frail people. Robust people are able to survive COVID infection without hospitalisation.
  • But a frail (weak) person will need more support during the same infection. Thus they are more likely to be hospitalised. In that subgroup, the authors found “lower Vaccine Effectiveness”.
  • It wasn’t “because they did not exercise” but rather “because they could not exercise”. It is also true that not exercising at all will increase frailty.

What is frailty?

  • The presence of weakness, loss of muscular strength with sarcopenia (muscle loss), reduced speed of walking and reduced physical activity is termed frailty. This can happen from years of being sedentary, not eating healthy food, or not taking care of one’s health in general.
  • Although it is more common with older people, even younger people can be frail if they fulfil the above criteria. It is well-established that individuals with frailty get more complications even with minor illnesses.
  • Now, let’s look at the study results.
  • When the authors compared vaccinated people with unvaccinated, hospitalisations (as expected) were lower among vaccinated.
  • But among the vaccinated people, the authors spotted a difference between those who did regular exercise and those who did not do exercise.
  • It is quite likely that among the people who were not exercising were more individuals with frailty – who naturally required more support while having a bout of Covid 19. Thus they were hospitalised more, which was interpreted as lower vaccine effectiveness.


  • Correlation is not causation. Vaccination reduces need for hospitalisation from COVID. Among the vaccinated people who got COVID, those who were the healthiest at baseline did best – requiring least hospitalisation.
  • Seeing this study, some people might start exercising excessively after vaccination. Exercise is good for long-term health. But there is no need to suddenly start exercising upon receiving a vaccine dose, as the study seems to be suggesting.
  • Severe exercise immediately after vaccination might not be good for health, because the body is in a state of inflammation, many have muscle pains and fever. (We were the first to report the safety of COVID vaccination in India, and found that upto 2/3 individuals have transient symptoms that go away on their own).


  1. Measuring frailty in younger populations: a rapid review of evidence | BMJ Open
  2. Collie S, Saggers RT, Bandini R, et alAssociation between regular physical activity and the protective effect of vaccination against SARS-CoV-2 in a South African case–control studyBritish Journal of Sports Medicine Published Online First: 24 October 2022. doi: 10.1136/bjsports-2022-105734

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