COVID-19 really does seem less deadly when you give people the...

This is suggested by a study conducted in Mexico in which 255 people with an increased risk of COVID-19 were given the vaccine.

Of the 255 people, 36 actually contracted the corona virus. And all of them developed symptoms that were much milder than you would expect based on their health status and age. Researchers write this in the magazine Allergy.

Trained immunity
It may seem a bit strange that a vaccine that has not been developed to protect against COVID-19 does anyway. But it’s not as far-fetched as it sounds. After years of research, we now know that there is such a thing as ‘trained immunity’. It actually means that you can give the immune system extra protection against a disease by exposing it to a completely different, unrelated pathogen.

What seemed a controversial idea in the 1980s – when researchers showed that African children vaccinated against measles also developed greater resistance to other infectious diseases – is in 2020 – partly due to the efforts of the Dutch researcher Mihai Netea – has become an accepted idea. By exposing people to a (weakened) pathogen through vaccination, you can ensure that the immune system also reacts much faster and more effectively when exposed to a completely different pathogen, making the disease progression milder. And so some vaccines – such as the measles vaccine – can not only prevent people from contracting the disease being vaccinated against, but also help people to cope with other pathogens.

BCG and BMR
That idea – which has since been proven, partly thanks to Netea – came back to the center of attention when the coronavirus SARS-CoV-2 quickly spread across the world at the beginning of this year. There is no vaccine. And so researchers started looking for ways to give our immune system an extra boost, so that it could better cope with the virus in the event of an encounter with SARS-CoV-2. Netea is currently experimenting in the Netherlands with the BCG vaccine, for example, which has been developed to protect against tuberculosis, but may also lead to a milder course of COVID-19 by means of the trained immunity described above. And in Mexico, under the leadership of Dr Desiree Larenas-Linneman, originally from the Netherlands and very familiar with Netea’s work, they focused on the MMR vaccine.

The research
This vaccine – which is also part of the national vaccination program in the Netherlands – originally offers protection against mumps, measles and rubella. But earlier this year, researchers already suggested that the vaccine may also be used to boost our immune system, so that it can act quickly when exposed to SARS-CoV-2 and the infectious disease progresses more gently. Research led by Larenas-Linneman now seems to endorse this.

The study took place in Mexico, where the rise of SARS-CoV-2 coincided with a sudden increase in the number of people who got measles. The Mexican Ministry of Health therefore called on people to have themselves vaccinated against measles again, which actually created the ideal conditions for testing the idea that the MMR vaccine could protect against COVID-19. From March, the researchers recommended that all their patients get vaccinated against measles.

Results
Subsequently, 255 of these measles-vaccinated individuals were closely monitored. This mainly concerned people who – because they were related to or cared for COVID-19 patients – were much more likely to contract COVID-19. 36 of the vaccinated people contracted the corona virus in the following months. Thirteen of them had an increased risk of a serious disease course because they had high blood pressure, diabetes, smoked or were obese, for example. Nevertheless, the viral infection was mild in all subjects. And no subject needed supplemental oxygen. “We were relieved that the MMR vaccine – usually seen as a vaccine for children – also appears to be helping older adult patients weather the storm,” said Larenas-Linneman.

Follow-up research
While the results are promising, more research is needed to determine with certainty that the vaccine really offers protection. But that is being worked on. A so-called randomised trial set up among first aid and care providers. Some of the subjects will receive the measles vaccine and another part will serve as a control group, and then it will have to be shown over time whether viral infections in the group that received the MMR vaccine are significantly milder than in the control group. Researchers also plan to set up a study in nursing homes.

BCG versus BMR
In the meantime, research is continuing in the Netherlands into the BCG vaccine. In September, a major study started in 22 hospitals where the vaccine is offered to vulnerable elderly people. The research must show whether this target group – who has an increased risk of dying from COVID-19 – will benefit from the vaccine. If so, it could possibly be administered preventively to risk groups and caregivers. Vaccinating everyone seems to be difficult. Tuberculosis – with about 1.5 million deaths per year – is still the most deadly infectious disease on earth and the vaccines are therefore desperately needed to protect children worldwide against the disease. For Larenas-Linneman and colleagues, it is one of the reasons to look further and to focus on the MMR vaccine.

Of course, worldwide work is also underway on a vaccine that is specifically intended to prevent infection by SARS-CoV-2. However, it is still very uncertain when a proven effective and safe vaccine will become available. And so researchers are also continuing to look at the possibilities that existing vaccines offer. Much to the delight of Peter Aaby, a pioneer in the field of trained immunity: “Now that the corona crisis is urgent, it is very good to see that the potential of non-specific immune effects is also being taken seriously.”

Share