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- One of the oldest vaccines to exist, BCG, may offer protection against the world's newest infectious disease, Covid-19
- In addition to this vaccine, the MMR vaccine is also currently being trialled globally to see if it offers the same benefit
- According to two independent studies recently published, MMR reduced Covid-19 severity in participants, while BCG reduced the chances of contracting Covid-19
Scientists have been looking at existing vaccines to see whether they could also induce protection against Covid-19, the disease caused by SARS-CoV-2. Among them are the measles-mumps-rubella (MMR) vaccine, as well as the decades-old tuberculosis vaccine, Bacillus Calmette-Guérin (BCG).
In a new study published in mBio, an open-access journal of the American Society for Microbiology, researchers provide evidence that in the MMR vaccine, mumps IgG titers (also known as levels of IgG antibody) are inversely correlated with severity in recovered Covid-19 patients previously vaccinated with the MMR II vaccine produced by Merck.
And, according to a new study by Cedars-Sinai, BCG is associated with reduced likelihood of contracting Covid-19. The study was published in the Journal of Clinical Investigation.
Why the MMR vaccine?
The MMR vaccine has been looked at as a possibility to work against Covid-19 since the early months of the pandemic, as it is known to protect against viruses that are similar to the coronavirus.
The World Health Organization (WHO) states that the vaccine is widely used for the immunisation of children in certain regions of the world due to its advantages over individual vaccines.
The vaccine, which was developed almost 50 years ago, has since been received by hundreds of millions of people worldwide.
Countries involved in a study launched earlier this year include Canada, Ghana, Ireland, South Africa, Uganda, the UK, the US, Zambia and Zimbabwe, Health24 reported.
“... This type of vaccine, which contains small amounts of very weakened measles, mumps and rubella viruses, appears to strengthen the body’s immune response to infections in general, not just to the viruses in that particular vaccine,” said Sinead Delany-Moretlwe, one of the SA trial’s national principal investigators, and a research professor at the Wits Reproductive Health and HIV Institute (Wits RHI).
Another reason it may be effective is that there are similarities between the weakened viruses in the vaccine and the Covid-19 virus, Delany-Moretlwe explained.
The researchers commented that all of these viruses have similar proteins on their surfaces that are involved in infecting cells in the body, and they therefore hypothesise that antibodies made in response to the MMR vaccine may also recognise and fight SARS-CoV-2.
About the more recent study, lead study author Jeffrey Gold, president of World Organization in Watkinsville, Georgia, said: "We found a statistically significant inverse correlation between mumps titer levels and Covid-19 severity in people under age 42 who have had MMR II vaccinations.
"This adds to other associations demonstrating that the MMR vaccine may be protective against Covid-19. It also may explain why children have a much lower Covid-19 case rate than adults, as well as a much lower death rate.”
The majority of children get their first MMR vaccination around 12 to 15 months of age and a second one from 4 to 6 years of age, commented Gold.
Co-author David Hurley, professor and molecular microbiologist at the University of Georgia, also commented: "The MMR II vaccine is considered a safe vaccine with very few side effects. If it has the ultimate benefit of preventing infection from Covid-19, preventing the spread of Covid-19, reducing the severity of it, or a combination of any or all of those, it is a very high reward low risk ratio intervention.
“Maximum seropositivity is achieved through two vaccinations at least 28 days apart. Based upon our study, it would be prudent to vaccinate those over 40 regardless of whether or not they already have high serum MMR titers."
TB vaccine linked to lower risk of contracting Covid
The BCG vaccine was developed between 1908 and 1921 and is given to more than 100 million children around the globe every year.
Researchers have been studying BCG’s potential to curb illnesses other than TB for several years, in part because of a concept scientists call “trained immunity”, explains this article by Bhekisisa.
Researchers think that immunisations such as BCG and measles, the article explains, help reprogramme our immune cells to better respond to infections later.
A 2014 research review published in the Journal of Clinical Infectious Disease, for instance, found that BCG worked effectively to protect children against TB in northern countries, which typically have lower burdens of TB.
Researchers of the Cedars-Sinai study tested the blood of more than 6 000 healthcare workers in the Cedars-Sinai Health System for evidence of antibodies to SARS-CoV-2. Participants were also asked about their medical and vaccination histories.
The findings reveal that those who had received BCG vaccinations in the past (nearly 30% of participants) were significantly less likely to test positive for SARS-CoV-2 antibodies in their blood or to report having had infections with coronavirus or coronavirus-associated symptoms over the previous six months, compared to those who had not received BCG.
These effects were not related to whether workers had received meningococcal, pneumococcal or influenza vaccinations.
However, the reasons for the lower SARS-CoV-2 antibody levels in the BCG group were not clear, according to Moshe Arditi, MD, director of the Paediatric and Infectious Diseases and Immunology Division at Cedars-Sinai and co-senior author of the study.
"It appears that BCG-vaccinated individuals either may have been less sick and therefore produced fewer anti-SARS-CoV-2 antibodies, or they may have mounted a more efficient cellular immune response against the virus," said Arditi.
"We were interested in studying the BCG vaccine because it has long been known to have a general protective effect against a range of bacterial and viral diseases other than TB, including neonatal sepsis and respiratory infections."
Based on their study results, co-author Susan Cheng, associate professor of Cardiology and director of Public Health Research at the Smidt Heart Institute at Cedars-Sinai, believes that large, randomised clinical trials are urgently needed to confirm whether BCG vaccination can induce a protective effect against SARS-CoV2 infection.
"It would be wonderful if one of the oldest vaccines that we have could help defeat the world's newest pandemic," commented Arditi.
READ | What the latest science says about a TB vaccine and Covid-19
WATCH | Why are scientists testing a TB vaccine to see if it protects against Covid-19?
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