Why Older People are Least Likely to Respond to COVID-19 Vaccine
Sat, April 17, 2021

Why Older People are Least Likely to Respond to COVID-19 Vaccine




The availability of a COVID-19 vaccine will be the biggest step in ending the pandemic. However, it may be the least effective among older people. This is because older people have an aging immune system, which unlikely to respond at best to vaccines.

The reconsideration of old age in vaccine creation was demonstrated in a preliminary report of a trialed COVID-19 vaccine. Researchers focused on healthy adults aged up to 55 years to determine the efficacy of the investigative vaccine. The objective was to stimulate the aging immune system to fight the SARS-CoV-2 virus. Fortunately, the results were a success in triggering immune responses across all participants. They published their findings in The New England Journal of Medicine.


The COVID-19 Vaccine and Older People

Among many parts of the human body, the thymus gland has been the last to be fully realized in terms of function. Before scientific evidence was uncovered, scientists had no idea that the gland would eventually shrink and be replaced by fatty tissue. The shrinkage would take place for years as a person ages. And by the time they reach the elderly, the gland had exhausted itself. But theoretically, the thymus gland would lose its entire function when the person reaches a little over 100 years old.

The consequence of the gland’s shrinking or thymus involution has been revealed 30 years after an older study, which identified the involution. Scientists finally discovered that the thymus gland is the source of T cells – a type of white blood cell capable of fighting different kinds of infections. The gland played a huge role in adaptive immunity or the last line of defense of the human body comprised of T and B cells, and antibodies. Without the gland, a person would not have mature T cells to protect the body from invaders.

Today, the role of the thymus in the fight against COVID-19 is highly correlated to vaccines. Vaccines are designed to induce natural immunity without risking a person from serious complications. But vaccines consist of either dead or alive, weakened pathogens to induce immunity. Oftentimes, live vaccines are easier to produce due to various reasons, such as cost-efficiency and low dependence on boosters. And for this pandemic, there is a chance that the first vaccine may be a live one.

The administration of a live vaccine has a risk of triggering an infection and complication. That risk is usually associated with specific population groups, including the elderly, people with chronic illnesses, and people with compromised immune systems. So, the best way to protect them is to vaccinate 70% to 90% of communities to form herd immunity. This begins by conducting vaccination programs among the youth.

If applied in COVID-19, the vaccine will be introduced to young, healthy individuals to stop the transmission and protect those who cannot receive the drug. But some researchers do not favor commercializing a vaccine that excludes older people.





Prototype mRNA Vaccine Tested Among Older People

According to the US Centers for Disease Control and Prevention, most cases of COVID-19 involved older people and individuals with pre-existing health conditions. In the case-based surveillance from February 12 to May 18, 2020, a total of 52,166 deaths from 47 jurisdictions in the US were laboratory-confirmed cases of COVID-19. Out of those deaths, 55.4% were male, 79.6% were aged at least 65 years, 13.8% were Hispanic or Latino, 21% were Black, 40.3% were White, 3.9% were Asian, 0.3% were American Indian or Alaska Native, 0.1% were Native Hawaiian or Pacific Islander, 2.6% were multiracial, and 18% were from unknown ancestries. An additional 10,647 COVID-19 deaths that occurred between February 12 and April 24, 2020, were included as supplemental surveillance. Out of that, 74.8% were aged at least 65 years.

In the supplemental surveillance, 74.1% of aged 65 years and older had at least one medical condition. About 51.8% had at least two medical conditions and 28.3% had at least three medical conditions. If scaled globally, hundreds of thousands of COVID-19 patients aged 65 years and older suffered from one medical condition. And if a vaccine was tailored for their age, their bodies might have a greater chance of overcoming the illness.

Recently, a clinical trial for an investigated drug included older people. A total of 45 healthy adults aged 18 to 55 years qualified in the trial. They were randomly assigned into three groups and received two doses of the drug 28 days apart. Each group of 15 participants received the mRNA-1273 in either dose of 25 micrograms, 100 micrograms, or 250 micrograms. More than 50% of the participants reported side effects like chills, fatigue, headache, myalgia, and pain at the injection site. But 21% of participants in the 250-microgram group reported more severe side effects.




Despite the adverse reactions, all participants expressed immune responses against SARS-CoV-2. The results supported the further development of the said vaccine. The findings showed that even older people could be vaccinated for COVID-19 provided the vaccine is determined safe for in-human use.

“Up until very recently most of the focus of the vaccine community has been on saving lives of young children. The people who need the vaccine the most may actually be the people in whom the vaccine might not work,” said Martin Friede, coordinator for vaccine product and delivery research at the World Health Organization, quoted American television network National Geographic.

In vaccine research, biomedical scientists have learned enough over the years the dysfunction in the human immune system associated with aging – immunosenescence. The dysfunction became apparent in older people who are prone to influenza, and in older people who received less protection from flu shots. Some vaccine makers formulated vaccines with more antigens to help stimulate an aging immune system. While others started making high-dose variants that are more effective than regular variants.

Any method to overcome immunosenescence is crucial in boosting vaccine benefits that older people can get. The reason is the dysfunction and the aging of the thymus gland contribute to the weakness of both adaptive and innate immune responses. On top of that, the aging immune system is constantly busy fighting off lifelong infections. The benign cytomegalovirus or CMV is one of those that the immune system contains round-the-clock. The constant engagement to that infection requires a percentage of the immune system, which means, it cannot fight a novel infection at 100%.

There are numerous challenges in developing the first COVID-19 vaccine. Most of the information scientists have learned are from the past months of this pandemic. Though, it does not mean they cannot utilize recognized information about viruses and immunity. Hopefully, the first vaccine will be compatible with all ages and affordable for everyone.