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Will a COVID-19 vaccine work in people with underlying medical conditions?

woman receives vaccine in a clinic
Written by Paul Taylor

Question: I have an autoimmune disease and need to take drugs that suppress my immune system. Should I get a COVID-19 vaccine when it becomes available? I worry that the shot won’t protect me from getting infected. Or worse, I might actually catch COVID from the vaccine.

Answer: You can rest assured that a COVID vaccine won’t give you the illness that it is designed to prevent.

Consider, for example, that two of the leading vaccine candidates are based on a new type of vaccine technology using messenger RNA – or mRNA. To create immunity, the vaccines contain some of the genetic instructions for SARS-CoV-2, the novel coronavirus that causes COVID-19.

“It’s only one strand of RNA for making a part of the virus – not the entire virus – and it’s not infectious,” says Dr. Rob Kozak, a scientist and clinical microbiologist at Sunnybrook Health Sciences Centre in Toronto. And the other promising vaccines don’t contain infectious agents either. “So, there is no risk of these vaccines making you sick with COVID.”

However, he adds that it’s harder to predict how well the vaccines will work in people with underlying medical conditions.

Preliminary data from trials of healthy adults indicate some of the experimental vaccines are effective in 90 to 95 per cent of those who receive two doses.

An encouraging sign is that some of the trials included volunteers over the age of 65 who tend to have less efficient immune systems than younger folks.

Dr. Kozak notes that a new vaccine from AstraZeneca has produced a comparatively strong immune reaction in older adults.  “This suggests the vaccines will probably work to some degree in people who are immune compromised.”

Nonetheless, we won’t know the true protective capacity of the vaccines until there are results from trials involving a broader segment of the population, including individuals with various medical conditions.

Indeed, many questions remain unanswered.

The main goal of a vaccine is to get your immune system ready to fight off a specific microbial invader.

Traditionally, vaccines have used weakened or dead viruses – or parts of viruses – to train the immune system. When exposed to a harmless de-activated virus in this way, the body will produce antibodies and other immune cells that are primed for a rapid attack if they encounter the real live pathogen.

In recent months, the threat posed by the global pandemic has helped accelerate the development of new and innovative vaccine technologies – including mRNA.

Several pharmaceutical companies – such as Pfizer and Moderna – are banking on this approach. Their mRNA vaccines contain the genetic code for producing “spike” proteins – the distinctive protrusions that dot the surface of the coronavirus.

When delivered in a vaccine, the mRNA enters the body’s cells and instructs them to churn out spike proteins.  Human cells immediately recognize these are “foreign” proteins and alert the immune system to start generating protective antibodies.

The key advantage of an mRNA vaccine is that the synthetic raw materials can be produced faster than some traditional vaccines, like flu shots, which rely on viral samples grown in eggs.

But, on the downside, mRNA is inherently unstable. The Pfizer vaccine, for instance, must be stored at minus 70 degrees Celsius – creating huge challenges for distributing the doses.

The other promising vaccine is being developed by the University of Oxford and its pharmaceutical partner AstraZeneca. They are using a genetically-altered cold virus to deliver spike protein genes to trigger an immune response.

And there are still more vaccines in the pipeline. “No one expects that just a few companies will be able to produce enough vaccine to inoculate the entire world before next fall,” says Dr. Kozak. “So, we absolutely need more.”

Another uncertainty is that we don’t how long the vaccinations will last. Immunity may wane over time, requiring booster shots down the road.

But the more immediate question is whether the vaccines will actually block infection or just reduce the severity of the illness.

Even if a vaccine only minimizes symptoms, that may be sufficient to prevent a surge in COVID-19 cases from overwhelming the health-care system, says Dr. Chris Labos, an epidemiologist and cardiologist in Montreal.

“If the symptoms are reduced, then fewer people will need to be admitted to hospital, and fewer of them will be taking up ICU (Intensive Care Unit) beds and ventilators.”

On the other hand, if you are inoculated and only have partial immunity, you might later contract a mild case of COVID and still be capable of spreading it to others.  As a result, we may need to take protective measures to guard against infections until enough people are vaccinated to create collective “herd” immunity.

“Just because a vaccine is rolled out, it doesn’t necessarily mean we stop wearing masks or keeping our distance,” says Dr. Labos.

Dr. Kozak agrees: “I think masks are going to be with us for a while.”

About the author

Paul Taylor

Paul Taylor retired from his role as Sunnybrook's Patient Navigation Advisor in 2020. From 2013 to 2020, he wrote a regular column in which he provided advice and answered questions from patients and their families. Follow Paul on Twitter @epaultaylor