Rachel Strohm

Rachel Strohm was an active hiker, cycler and rock climber before long COVID felled her in December, 2021.

As a researcher in international development, travel vaccines for low-income countries are a typical part of my life. But I never expected that once I developed Long COVID, a travel vaccine for Japanese encephalitis might help me make a rapid recovery. Could similar vaccines hold clues to fighting Long COVID?

Long COVID: Fatigue and Frustration

My Long COVID journey began in December 2021, when I tested positive at the height of the first Omicron wave. Thanks to my previous Johnson & Johnson vaccination, it was a mild case, with the only real symptom being fatigue. After isolating for ten days, I went back to work. But I quickly found that I was struggling to re-engage.

I’d previously balanced full-time work with an active schedule of hiking, cycling, and rock climbing, but now I was pushing myself through one workday and feeling too tired to get out of bed the next. The fatigue and brain fog quickly worsened, and soon I could only stand up or focus for about an hour per day. No amount of rest, dietary changes, or supplements was helping. By March 2022, I had to go on leave from my job.

At the time, there weren’t any Long COVID specialists in Kenya, where I’ve lived since 2017. So I traveled back to Chicago to stay with my family there and enrolled at the Long COVID clinic at Northwestern Memorial Hospital. However, they couldn’t offer much for the fatigue. I left my first appointment feeling quite dejected.

The Japanese Encephalitis Vaccine

Separately from the Long COVID issue, I also needed to update some of my travel vaccines. In April 2022, I got boosters for meningitis; typhoid; tetanus, diphtheria, and pertussis (Tdap). I also got a new-to-me vaccine against the Japanese encephalitis virus (JEV), the first of a two-dose series. Despite the name, JEV is found across Asia, and I’d been planning a trip to India before I got sick. I decided to get the vaccine as long as I was at the travel clinic, just in case I ever recovered enough to travel.


Rachel received an array of vaccines – one of which was new to her.

The days after that first travel clinic appointment passed in the usual haze of fatigue and brain fog. Then I went back for my second dose of the JEV vaccine the following week. Within hours of the second dose, I felt my energy levels starting to improve. That was the first day in months that I hadn’t needed an afternoon nap.

I woke up the next day absolutely buzzing with energy. I had another appointment at Northwestern that morning, and afterwards I went across the street to an art museum and walked around for hours. I didn’t even take a nap when I got home later.

The buzzing feeling lasted for almost 10 days. I woke up early, completed my tasks for the day, started taking longer walks, and didn’t even crash the next day. I subsequently got appendicitis in late April, which killed the buzz, but I was back on my feet just days after surgery and had an easy recovery.

For ten months since then, my energy levels have consistently been about 90% of what they were pre-pandemic. I do need to rest more than I did before COVID-19, and I’ll still sometimes have a bad fatigue day if I push too hard during a workout, but thankfully this is rare. My cognition is totally back to normal, and I’m planning to finish some Ph.D. research that I’d paused earlier in the pandemic. It’s been a huge relief to be able to pick up my career again.

Vaccines and Trained Immunity

Innate immune system in action

Innate immune system in action (Danijela Petrovic, Mariana Seke, Branislava Srdjenovic, Aleksandar Djordjevic, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons).

Did the JEV vaccine really help me to recover from Long COVID, or was it just a quirk of timing in a recovery that I might have made anyway? I can’t make any causal claims about this from a single case study. But after reading a great deal of additional medical literature, I’ve come to believe that the vaccine may have helped my body clear viral reservoirs of SARS-CoV-2 which were likely contributing to my Long COVID fatigue (Choutka et al. 2022, Davis et al. 2022).

While this precise phenomenon has not been documented for the JEV vaccine and post-viral illnesses before, there’s a large amount of evidence showing that certain types of vaccines can help the body fight off unrelated viruses, in a process called trained immunity.

To understand trained immunity, let’s note that the human immune system is made up of two parts: the innate (general) and adaptive (specialized) immune systems. The innate immune system responds quickly to all foreign substances or germs. If the innate immune system can’t fight off a germ, this activates the adaptive immune system, which can respond to a specific bacteria or virus. The adaptive immune system may take some time to identify a new bacteria or virus, but once it has done so, it is able to remember that stimulus and respond quickly in the future.

Researchers used to believe that only the adaptive immune system had this type of immunological memory. However, recent studies have shown that the innate immune system can also improve its response to new types of viruses if it’s previously been exposed to a similar virus – often delivered through a vaccine. This is referred to as “trained immunity” of the innate immune system (Naik & Fuchs 2022, Netea et al. 2020).

In other words, getting a vaccine against one virus can help the innate immune system respond more efficiently to other viruses in the future. This may lower the risk of getting sick or reduce the severity of symptoms if one does get sick. Vaccines that can generate this type of trained immunity are also referred to as having non-specific or heterologous effects.

BCG Vaccine

One of the vaccines that have been most widely documented to generate trained immunity is the Bacillus Calmette-Guérin (BCG) vaccine. BCG is the live attenuated vaccine used against tuberculosis in many countries. Many studies have observed that children who are given this vaccine are also less likely to die of other respiratory illnesses (Aaby & Benn 2019, Arts et al. 2018, Lobo et al. 2021, Sohrabi et al. 2020). Similar effects have been found for the live attenuated measles, mumps, and rubella (MMR) vaccine and the live attenuated oral poliovirus vaccine (OPV) (Hutson 2022, Sørup et al. 2015).

While the trained immunity generated by these vaccines does offer an important source of protection from other viral illnesses, it also has its limitations. The vaccines don’t consistently generate trained immunity for everyone (Hutson 2022). The amount of non-specific protection offered by the vaccine may depend on whether or not it’s co-administered with other vaccines, which is particularly common for children (Aaby & Benn 2019). And the protective effect wanes over time, although it can be improved by boosters which are given to adolescents or adults (Sohrabi et al. 2020).

Trained Immunity for Post-Viral Illnesses?

Viruses and bacteria

Getting vaccinated against a different virus may have helped Rachel fight off the coronavirus.

If some cases of Long COVID are generated by viral reservoirs of SARS-CoV-2, then it certainly seems plausible that an unrelated vaccine that generates trained immunity might help the body fight off the lingering virus. Research on the specific topic of trained immunity for post-viral illnesses is limited, but there is some intriguing evidence around BCG, JEV, and acute COVID-19 infection which suggests that this hypothesis warrants further research.

Here are some key questions and answers on the topic.


Is there any evidence that vaccines like BCG or JEV can help people recover from Long COVID, or other post-viral illnesses?

Because dysfunction of the innate immune system is implicated in many post-viral illnesses, including myalgic encephalitis/chronic fatigue syndrome (ME/CFS) (Brenu 2014), a vaccine that helped train the innate immune system might help. At present, though, there do not seem to be any studies addressing this specific question. Most of the existing research looks at whether these vaccines can help to prevent a novel infection with an unrelated virus, rather than clearing an existing infection. Therefore, the impact of trained immunity might not be the same for acute vs. post-viral illness (Hirschenberger et al. 2021).

Notarte et al. (2022) review the experimental literature on whether people with Long COVID benefit specifically from COVID-19 vaccines, but find that some people improve and others worsen after receiving the vaccine, so the results are not conclusive. And Renz-Polster (2022) summarizes some of the pathways by which the BCG vaccine might affect individuals with Long COVID or ME/CFS. Renz-Polster reports that BCG vaccination has documented anti-viral effects on human herpesviruses and that several studies have found BCG vaccination slowed or prevented progression in multiple sclerosis – a disease associated, like ME/CFS, with Epstein-Barr virus (EBV) reactivation.

Given the lack of evidence on Long COVID, do we know if vaccines like BCG or JEV offer protection from acute infection with SARS-CoV-2?

The evidence on the effects of non-COVID-19 vaccines is mixed. Two observational studies from July-August 2020 found that higher national rates of childhood BCG vaccination were associated with fewer COVID-19 deaths per million people, although it’s not clear if this finding would have held for later variants like Delta or Omicron (Berg et al. 2020, Escobar et al. 2020).

An experimental study in Greece showed that elderly people who received a BCG booster were less likely to contact COVID-19 (Tsilika et al. 2021). However, studies in the Netherlands and South Africa found BCG boosters for adults had no effect on the likelihood of contacting COVID-19 (Bonten et al. 2021, Upton et al. 2022). A number of other studies of BCG and acute COVID-19 infection are ongoing, as summarized by Lobo et al. (2021). Looking beyond BCG, a study in Qatar suggests that the flu vaccine also offers protection against acute COVID-19 infection (Tayar et al. 2022). There are no studies of the JEV vaccine and COVID-19 infection.

The Gist

  • An avid cyclist, hiker, and rock climber, international development policy specialist Rachel Strohm was in excellent shape before she went toe to toe with the coronavirus.
  • It began with a mild case of COVID-19 in December, 2021. Seemingly quickly recovering, she returned to work but faded quickly, and three months later, she was on leave and on a flight from her home in Kenya to Chicago to seek help.
  • She didn’t get any help from doctors but did from an unexpected arena. Rachel’s job left her no stranger to getting vaccinated against all sorts of diseases. Back in Chicago, she went to a travel clinic for booster shots for meningitis; typhoid; and tetanus, diphtheria and pertussis (Tdap) as well as the first of a two vaccine shots against the Japanese encephalitis virus (JEV).
  • A week later, she received a second JEV shot, and felt her energy levels start to improve within hours. She woke up the next day “absolutely buzzing with energy,” and was immediately able to return to normal activities, like a long day walking around museums without fatigue.
  • The buzzing feeling lasted for 10 days, stopped only by a case of appendicitis, from which she quickly recovered. In the 10 months since then, her energy levels have been about 90% of what they were pre-long COVID, and she’s been able to pick up her career again.
  • So how did a vaccine against a different virus almost totally cure Rachel’s long COVID? Her research suggests the answer may lie in something called “trained immunity”, which occurs when vaccines against one virus help to clear the body of other viruses.
  • Vaccines are targeted at boosting the adaptive immune response – the immune response that kicks in several days after the infection and zeros in directly on the pathogen. In trained immunity, though, vaccines against one pathogen appear to boost the early or innate immune system’s ability to fight off an infection.
  • Vaccination with the Bacillus Calmette-Guérin (BCG) vaccine as well as attenuated measles, mumps and rubella (MMR) vaccines have all been shown to enhance responses to other pathogens. The effect doesn’t show up for everyone and may be less powerful when one vaccine is administered with others. Nor has the “trained immunity” hypothesis been tested in diseases like long COVID where the virus may be lingering.
  • Still, studies suggest the innate immune response in post-infectious diseases like ME/CFS is impaired, and anything that helps it work better could help clear an unresolved infection. Plus, the BCG virus does appear to help knock down herpesvirus reactivation – possibly a key factor in both ME/CFS and long COVID.
  • Neither BCG nor JEV has been tested against long COVID, but BCG’s ability to impact COVID-19 is mixed with some studies saying yes, and others no. With regard to the JEV vaccine Rachel received, several mouse studies suggest it may help protect against other viruses.
  • The JEV vaccine’s effect on any one person with long COVID, though, is unclear and could be impacted by a number of factors, including what viruses and vaccines they’ve been exposed to in the past, and whether the coronavirus is actually persisting in them.
  • It’s possible that Rachel caught a lucky break with the JEV vaccine. The fact that she’d never been exposed to the vaccine before and had not been ill long may have helped.
  • The JEV vaccines’ rapid and striking effect on her long COVID, though, and the ready availability of other vaccines like BCG, oral polio vaccine (OPV), measles, mumps and rubella (MMR) – some of which have been shown to induce trained immunity – suggests that further investigations into whether vaccine-induced trained immunity can clear up long COVID in some people are warranted.

Of the various vaccines which can generate trained immunity, which ones might be most useful for treating acute or Long COVID?

Vaccines that can generate trained immunity have not been directly compared to each other. Generally speaking, the evidence suggests that live attenuated vaccines have a stronger protective effect than inactivated vaccines (Aaby & Benn 2019).

The JEV vaccine (Ixiaro) is inactivated. Why do you think it seemed to help you?

There’s a limited evidence base on trained immunity from the JEV vaccine. Two studies show that this vaccine can protect mice against novel viruses including Dengue and Zika (Li et al. 2016, Tarbe et al. 2020), but there’s no evidence in humans yet. A separate study shows that an inactivated vaccine made up of five types of bacteria offers protection against the flu virus in humans (Brandi et al. 2022). So there is some suggestion here that even inactivated vaccines can generate trained immunity, but much more research would be needed to document this conclusively.

Could everyone with Long COVID benefit from getting a vaccine like BCG or JEV?

While there is evidence that these types of vaccines may offer the immune system some support in clearing the SARS-CoV-2 virus, it seems unlikely that they will benefit everyone equally. Long COVID appears to affect the body through a number of underlying biological mechanisms, not just viral reservoirs (Davis et al. 2022, Koc et al. 2022).

These vaccines do not consistently generate trained immunity for everyone who receives them, given that people vary quite a lot in the number of viruses to which they’ve previously been exposed, and vaccines they’ve previously received (Sohrabi et al. 2020). Furthermore, live attenuated vaccines can pose some risk to people who are already immunocompromised (Miller & Wodi 2021), although in general, the BCG vaccine seems safe for adults recovering from acute COVID-19 (Dionato et al. 2022) and is well-tolerated in the broader population (Sohrabi et al. 2020). It may be worth discussing these vaccines with your doctor or your local travel clinic, but there’s no guarantee this is a cure for Long COVID.


To return to my own case for a moment, I personally feel that I caught a lucky break. By chance, I got a vaccine that appears to have generated some trained immunity and helped me recover from Long COVID. I suspect that part of this effect was due to the fact that the JEV vaccine was completely new to me, and I’ve often wondered if I would have received the same benefit from a booster for OPV or MMR, which I had already been exposed to as a child. I also had a limited range of symptoms compared to many Long COVID patients and had only been dealing with the illness for four months, so this may have facilitated a faster recovery once the viral reservoirs had been treated.

With these caveats noted, I do think that there’s huge potential in studying the use of existing vaccines to treat Long COVID. Vaccines such as BCG and OPV are safe and widely available in many countries outside the US, and the MMR and JEV vaccines are also available in the US. The lack of existing therapeutic options for Long COVID and other post-viral illnesses means that finding any accessible treatments should be a high priority.

About the Author

Rachel Strohm is the director of Social Policy Insights, a research consultancy based in Nairobi, Kenya. She holds an MA in political science from the University of California, Berkeley; an MA in international relations from Johns Hopkins University; and a BA in geography and French from Dartmouth College.


Aaby, P., and C.S. Benn. 2019. ‘Developing the Concept of Beneficial Non-Specific Effect of Live Vaccines with Epidemiological Studies’. Clinical Microbiology and Infection 25(12): 1459–67.

Arts, Rob J.W. et al. 2018. ‘BCG Vaccination Protects against Experimental Viral Infection in Humans through the Induction of Cytokines Associated with Trained Immunity’. Cell Host & Microbe 23(1): 89-100.e5.

Berg, Martha K. et al. 2020. ‘Mandated Bacillus Calmette-Guérin (BCG) Vaccination Predicts Flattened Curves for the Spread of COVID-19’. Science Advances 6(32): eabc1463.

Bonten, Marc, Mihai Netea, Frits Rosendaal, and Maurice van den Bosch. 2021. ‘Tuberculosis Vaccine Does Not Protect Vulnerable Elderly against COVID-19’. UMC Utrecht. https://www.umcutrecht.nl/en/over-ons/nieuws/details/jan-18-tuberculosis-vaccine-does-not-protect-vulnerable-elderly-against-covid-19 (February 7, 2023).

Brandi, Paola et al. 2022. ‘Trained Immunity Induction by the Inactivated Mucosal Vaccine MV130 Protects against Experimental Viral Respiratory Infections’. Cell Reports 38(1): 110184.

Choutka, Jan, Viraj Jansari, Mady Hornig, and Akiko Iwasaki. 2022. ‘Unexplained Post-Acute Infection Syndromes’. Nature Medicine 28(5): 911–23.

Davis, Hannah E., Lisa McCorkell, Julia Moore Vogel, and Eric J. Topol. 2023. ‘Long COVID: Major Findings, Mechanisms and Recommendations’. Nature Reviews Microbiology.

Dionato, Franciele A.V. et al. 2022. ‘BCG Vaccine Safety in COVID-19 Convalescent Adults: BATTLE a Randomized Controlled Trial’. Vaccine 40(32): 4603–8.

Escobar, Luis E., Alvaro Molina-Cruz, and Carolina Barillas-Mury. 2020. ‘BCG Vaccine Protection from Severe Coronavirus Disease 2019 (COVID-19)’. Proceedings of the National Academy of Sciences 117(30): 17720–26.

Hirschenberger, Maximilian, Victoria Hunszinger, and Konstantin Maria Johannes Sparrer. 2021. ‘Implications of Innate Immunity in Post-Acute Sequelae of Non-Persistent Viral Infections’. Cells 10(8): 2134.

Hutson, Matthew. 2022. ‘Beyond the Booster Shot | The New Yorker’. The New Yorker. https://www.newyorker.com/science/annals-of-medicine/beyond-the-booster-shot.

InformedHealth.org. 2020. InformedHealth.org [Internet] The Innate and Adaptive Immune Systems. Institute for Quality and Efficiency in Health Care (IQWiG). https://www.ncbi.nlm.nih.gov/books/NBK279396/ (February 7, 2023).

Koc, Ho Cheng et al. 2022. ‘Long COVID and Its Management’. International Journal of Biological Sciences 18(12): 4768–80.

Li, Jieqiong et al. 2016. ‘Cross-Protection Induced by Japanese Encephalitis Vaccines against Different Genotypes of Dengue Viruses in Mice’. Scientific Reports 6(1): 19953.

Lobo, Niyati et al. 2021. ‘100 Years of Bacillus Calmette–Guérin Immunotherapy: From Cattle to COVID-19’. Nature Reviews Urology 18(10): 611–22.

Naik, Shruti, and Elaine Fuchs. 2022. ‘Inflammatory Memory and Tissue Adaptation in Sickness and in Health’. Nature 607(7918): 249–55.

Netea, Mihai G. et al. 2020. ‘Defining Trained Immunity and Its Role in Health and Disease’. Nature Reviews Immunology 20(6): 375–88.

Notarte, Kin Israel et al. 2022. ‘Impact of COVID-19 Vaccination on the Risk of Developing Long-COVID and on Existing Long-COVID Symptoms: A Systematic Review’. eClinicalMedicine 53: 101624.

Okafor, Chika N., Ayesan Rewane, and Ifeanyi I. Momodu. 2022. ‘Bacillus Calmette Guerin’. In StatPearls, Treasure Island (FL): StatPearls Publishing. 

Raddad, Laith Jamal Abu. ‘Effectiveness of Influenza Vaccination against SARS-CoV-2 Infection among Healthcare Workers in Qatar’.

Renz-Polster, Herbert. 2022. ‘BCG Vaccination as a Treatment Option for ME/CFS and Post Covid Syndrome?’ https://www.kinder-verstehen.de/wp-content/uploads/BCG_hypothesis_short_251222.pdf.

Sohrabi, Yahya et al. 2020. ‘Trained Immunity as a Novel Approach against COVID‐19 with a Focus on Bacillus Calmette–Guérin Vaccine: Mechanisms, Challenges and Perspectives’. Clinical & Translational Immunology 9(12). 

Sørup, Signe et al. 2016. ‘Oral Polio Vaccination and Hospital Admissions With Non-Polio Infections in Denmark: Nationwide Retrospective Cohort Study’. Open Forum Infectious Diseases 3(1): ofv204.

Tarbe, Marion et al. 2020. ‘Japanese Encephalitis Virus Vaccination Elicits Cross-Reactive HLA-Class I-Restricted CD8 T Cell Response Against Zika Virus Infection’. Frontiers in Immunology 11: 577546.


Upton, Caryn M. et al. 2022. ‘Safety and Efficacy of BCG Re-Vaccination in Relation to COVID-19 Morbidity in Healthcare Workers: A Double-Blind, Randomised, Controlled, Phase 3 Trial’. eClinicalMedicine 48: 101414.

World Health Organization. ‘Japanese Encephalitis’. https://www.who.int/news-room/fact-sheets/detail/japanese-encephalitis (February 7, 2023).



Like the blog you're reading? Don't miss another one.

Get the most in-depth information available on the latest ME/CFS and FM treatment and research findings by registering for Health Rising's free  ME/CFS and Fibromyalgia blog here.

Stay on Top of the News!

Subscribe To Health Rising’s Free Information on Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM), Long COVID and Related Diseases.

Thank you for signing up!

Pin It on Pinterest

Share This