Story at a glance

  • Vaccines for tuberculosis and polio may provide some general immune benefits.
  • This effect hasn’t been widely studied yet, but there are some ongoing clinical trials.
  • The strategy could be helpful for boosting the immune systems of essential workers.

Researchers are exploring the possibility of giving existing vaccines to health care workers because of a nonspecific protection it may provide against infections. A few vaccines in particular are thought to give a short term boost to the immune system, though this has not been studied rigorously. Studies are now underway to examine whether there is a real benefit for giving these vaccines in the fight against SARS-CoV-2, the coronavirus that causes COVID-19, especially for essential workers.

Health experts have been aware of this potential side benefit of some vaccines for years. It has to do with innate immunity, which is the arm of the immune system that recognizes and attacks foreign particles. In particular, the Bacille Calmette-Guérin (BCG) vaccine for tuberculosis (TB) and the oral polio vaccine (OPV) for the poliovirus are the main vaccines that are being considered.

The BCG vaccine was in development for decades starting in the early 1900s and a safe strain of the vaccine was first tried in humans in 1921. It underwent many more years of research, and was more widely used starting after the 1950s. The BCG vaccine is not universally recommended in the U.S. but it is in many countries, including most of Asia and Africa.

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The OPV vaccine was first available in 1961 for the poliovirus that contains live attenuated, or less virulent, poliovirus. The different vaccine that is administered intravenously is called inactivated polio vaccine (IPV) and has been available since 1955. OPV is safe and effective, but IPV is preferable because the virus is inactivated. However, many countries still rely on OPV in the fight to eradicate polio because it is cheaper and easier to give to children.

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The boost to the immune system is called a nonspecific benefit because it isn’t particular to the pathogen that the vaccine was designed for. There is something that is happening with other aspects of the immune system that is helpful to the person dealing with infections. For example, this study suggests that the BCG vaccine induces a response that helps fight against an attenuated yellow fever virus vaccine. Some researchers have retroactively looked at SARS-CoV-2 infection rates in people who have received the BCG vaccine when they were infants compared to those who haven’t and didn’t find any statistically significant differences.


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This nonspecific vaccine approach would not be feasible to do on a large scale because there aren’t enough vaccine doses available to give to everyone. Another factor to consider is that the immune system boost, if there is one, may only last for a few months. Experts also don’t know if someone who has received the vaccine in the past would benefit from getting the vaccine again in the future.

While we are searching for an effective treatment and putting SARS-CoV-2 vaccine candidates through trials, this strategy could potentially help keep frontline workers healthy if it works. There are current clinical trials looking to find out. Health care workers could be given BCG or OPV vaccinations ahead of spikes in COVID-19 cases. It wouldn’t prevent them from getting exposed to SARS-CoV-2, but it could potentially help them fight off an infection if the coronavirus does get into their system.

For up-to-date information about COVID-19, check the websites of the Centers for Disease Control and Prevention and the World Health Organization. For updated global case counts, check this page maintained by Johns Hopkins University.

You can follow Chia-Yi Hou on Twitter.


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Published on Jun 26, 2020