COVID-19: Protecting vulnerable populations in a pandemic


14 October 2021

The last 18 months have seen incredible scientific advances in the fight against the global COVID-19 pandemic. Vaccines and other measures have had a significant impact in reducing the incidence of hospitalization and death from COVID-19.1 However, there remain groups of people, including those with compromised or suppressed immune systems, whose bodies may not mount a proper response to vaccines, including those for COVID-19.2-6 These vulnerable populations may need to take extra precautions, despite vaccination, and could benefit from additional protection.

How vaccines work

A vaccine uses inactivated virus or part of a virus to provoke an immune response within the body.7 This immune response, which starts within days and develops over a few weeks, involves the body’s own production of antibodies and T-cells which recognise the virus.8 The vaccine itself will not cause an infection, but if the person is later naturally exposed to a virus, the immune system is already primed and able to quickly work to neutralise and destroy the virus.8-9 This is what is referred to as active immunity.10

Vaccines and Vulnerable Populations

To work to their full potential, vaccines require a healthy immune system. However, millions of people around the world may be unable to mount an adequate response to a vaccine, due to an underlying health condition or medications they take that compromise or suppress their immune system.2-6,11In the case of COVID-19, this can leave them particularly vulnerable and without long-lasting protection against the disease, despite being fully vaccinated or having a previous SARS-CoV-2 infection.12-13 In addition, these immunocompromised individuals may already be at increased risk of poor outcomes from COVID-19 because their natural infection-fighting ability is diminished.14-15

Brian Koffman, MD, CM (retired), Co-Founder, Executive VP and Chief Medical Officer of the CLL (Chronic Lymphocytic Leukemia) Society, said: “Many people with blood cancers or people with other types of cancer being treated with chemotherapy do not produce the antibodies likely needed to prevent COVID-19 infection after vaccination. These patients, and others like them with weakened immune systems, will need something more than a vaccine in order to be fully protected and for them to feel confident and safe returning to their normal lives.”

Who May Need Additional Protection?

There are certain populations that are particularly vulnerable to having an inadequate or partial response to vaccination, meaning they remain susceptible to contracting a vaccine-preventable illness, including COVID-19. 2-6

Several health conditions and diseases can cause a person to be immunocompromised, including cancer, diabetes, kidney failure, lupus and rheumatoid arthritis.2-6,16 Some diseases like blood and bone marrow cancers affect the production or function of immune cells that can help prevent COVID-19 infection.15,17 Immunosuppressive drugs like chemotherapy may also deplete a variety of immune cells, including B-cells and inhibit the body’s natural ability to produce disease-fighting antibodies.15,18 Additionally, some medications or treatments for white-blood-cell cancers such as leukaemia and lymphoma, autoimmune diseases, and those used to help organ transplant patients can block the immune system from making protective antibodies.4,15,19 Certain infections such as HIV can also weaken immunity.2,16 You can also be born with a weak immune system (primary immune deficiency).20

Recent studies show that although immunocompromised patients represent less than 3% of the overall population, more than 40% of those hospitalised with breakthrough infections after vaccination are in people who are immunocompromised.12-13

Staying Ahead of COVID-19 and Ending the Pandemic

Currently, COVID-19 vaccination is generally recommended for those with weakened immune systems.15 In July 2021, the Centers for Disease Control and Prevention advised US health providers to counsel their immunocompromised patients about the potential for reduced immune response to COVID-19 vaccines and to continue to follow prevention measures until otherwise advised.15 In some countries, additional vaccine doses are now recommended for the immunocompromised.21 Emerging evidence for additional doses in this population suggests there is significant room to increase protection in these individuals.21

Accordingly, most health care professionals are still urging these individuals to take additional precautions, which can range from wearing masks, social distancing, working from home and, sometimes, still avoiding or minimising contact with other people.15 Research is underway to better understand immune responses after vaccination and how to best protect these vulnerable individuals. Scientists are also examining the role of other immune factors such as T-cells which could impact response to vaccination and severity of disease. While the active immune protection that comes from the vaccines is ideal, not everyone responds.2 Other options may be helpful for those who remain at high risk despite being fully vaccinated.

At AstraZeneca, we believe options that could offer long-lasting protection for the most high-risk populations are needed. Staying ahead of COVID-19 will help ensure as many people as possible around the globe are protected and help put the pandemic behind us.


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Date of preparation: September 2021