As the world grapples with the coronavirus disease (COVID-19) pandemic, scientists race to develop an effective vaccine to protect against the deadly SARS-CoV-2 virus. While potential vaccines are still being developed and tested, researchers propose that existing vaccines could give the immune system a temporary boost to ward off infection.
A team of researchers at the U.S. National Institutes of Health highlights the importance of repurposing vaccines, like the ones against polio and tuberculosis (TB), for other diseases, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.
Using old vaccines
Two tried-and-tested vaccines for polio and tuberculosis are being evaluated to see if they can offer limited protection against the coronavirus.
The Bacillus Calmette-Guerin (BCG) vaccine is given to infants and children in many countries across the globe. It protects against infection caused by Mycobacterium tuberculosis, which causes TB, a serious infection that affects the lungs and other parts of the body such as the joints, kidneys, and bones.
Mycobacterium tuberculosis is a pathogenic bacterial species in the family Mycobacteriaceae and the causative agent of most cases of tuberculosis. Image Credit: Tatiana Shepeleva / Shutterstock
Meanwhile, the polio vaccine comes in two forms – the inactivated polio vaccine (IPV) and the oral polio vaccine (OPV). The vaccine is given to children to reduce the risk of getting polio, which is a crippling and fatal disease caused by the poliovirus. The virus can attack the person’s brain and spinal cord, causing paralysis.
In the study, described in the journal Science, the team believes that the use of old vaccines may help curb the coronavirus pandemic. The team cited evidence that the polio vaccine has reduced mortality or sped up the recovery from other viral diseases, such as the flu and genital warts. Further, polio vaccination in children has been tied to lower rates of ear and respiratory infections, which are caused by bacteria or viruses.
Triggers a temporary immune system boost
The polio vaccine is a live vaccine, which means it is the weakened form of the virus. Live vaccines trigger an immune response that helps the body ward off invaders until the immune system has time to develop specific antibodies. The scientists think that using old vaccines can help boost the immune system’s power and could provide protection for viruses the vaccine was not designed to prevent, including the coronavirus.
“An increasing body of evidence suggests that live attenuated vaccines can also induce broader protection against unrelated pathogens likely by inducing interferon and other innate immune mechanisms that are yet to be identified,” the team wrote in the paper.
Attenuated bacterial vaccines, like the BCG against tuberculosis and the experimental live attenuated vaccine against whooping cough, have also shown effectiveness in protecting against heterologous infections.
Previous studies have shown that BCG activates the innate immune system, leading to enhanced responsiveness to other infections or triggers. This type of immunity is called “trained innate immunity.” The team also noted that BCG could induce a condition called emergency granulopoiesis within hours of being administered, leading to a marked increase in the number of circulating neutrophils, giving protection from sepsis.
“Recent reports indicate that COVID-19 may result in suppressed innate immune responses (15). Therefore, stimulation by live attenuated vaccines could increase resistance to infection by the causal virus, severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2). Clinical studies of this hypothesis could begin immediately,” the team said.
OPV over BCG
However, the team proposes the use of OPV over BCG to ameliorate or prevent COVID-19. The team explained that both the poliovirus and the coronavirus are positive-strand RNA viruses. This means that it is more likely to induce a temporary immune response against SARS-CoV-2.
Using OPV has many advantages, including a strong safety record, having more than one serotype that could be used for prolonged protection, easy availability, and affordability. In 140 countries, more than 1 billion doses of OPV are produced, while the BCG vaccine is limited.
Moreover, OPV is generally safe with a low risk of complications. On the other hand, up to 1 percent of BCG recipients develop adverse reactions.
“If the results of RCTs with OPV are positive, OPV could be used to protect the most vulnerable populations. However, OPV would be most effective if the entire population of a country or region is immunized synchronously,” the team explained.
“If proven to be effective against COVID-19, emergency immunization with live attenuated vaccines could be used for protection against other unrelated emerging pathogens,” the team added.
IPV vaccine for polio
IPV also called the Salk vaccine, is injected in the leg or arm, depending on age. IPV is given to a child at the age of 2, 4, and 6-18 months. A booster dose is needed at 4-6 years.
Adults usually do not need a polio vaccine if they have been vaccinated as children. However, those who are traveling to a place where there is a polio outbreak, those working with samples of poliovirus in a laboratory and those living in contact with a poliovirus infected person may need to be vaccinated.
Pregnant women, those with a suppressed immunity, and those with HIV require to be vaccinated with IPV. The adult regimen of vaccination is a 'first dose at any time' followed by the second dose 1 to 2 months later and a third dose 6 to 12 months after the second.
OPV vaccine for polio
OPV is also called the Sabin vaccine. It contains live but much-weakened poliovirus given as oral drops.
It helps the receiver’s immune system to recognize the virus and create antibodies against it so that when they are faced with the actual infection they may be able to fight it.
Another benefit of OPV is that children vaccinated with the drops excrete the vaccine virus that is much weakened.
The contacts of the child who are not vaccinated receive the dose of the vaccine virus second hand from them. This contains polio outbreaks and is important for the eradication of polio.
The coronavirus has infected more than 7.89 million people and has so far killed more than 432,000 individuals. While vaccines are still being developed and tested, using old vaccines for protection can help reduce the spread of the deadly virus.