The risk of serious illness or death associated with an infection increases with age. The body’s mechanisms that resist infections begin to weaken, on average, at age 50.

The risk to seniors associated with SARS-CoV-2 (the coronavirus that causes COVID-19) is primarily associated with a compromised immune system. Fatality rates associated with COVID-19 begin to increase significantly for patients in their 50s and become particularly high for patients in their 80s.

Averages only tell us about group populations. Some younger individuals may suffer from diseases that impair their immune systems while some older individuals may retain a strong ability to fight infection. In fact, data from Israel suggests that people between the ages of 50 to 59 recover from mild to moderate COVID-19 infections less quickly than people over the age of 60, although the differences in recovery times are slight.

Families should not lose hope when a senior acquires COVID-19. Ada Zanusso, an Italian who survived the Spanish Flu in 1918, made a full recovery from COVID-19 at the age of 104. Several other seniors over the age of 90 shine as beacons of hope after recovering from the infection. Most patients in their 80s have recovered from COVID-19.

Why some people of all ages suffer from only mild or moderate symptoms after becoming infected while others are hospitalized is unclear. Still, the impairment of the body’s immune system with aging does place seniors, as a group, in greater danger than younger people.

Immunity and Susceptibility to COVID-19

According to the Gerontological Society of America, the impairment of several bodily systems that fight infection accounts for the association between age and the risk of developing severe symptoms from COVID-19. Those systems include:

• Weakening of the hairs that push mucus out of the lungs, resulting in a prolonged exposure to viruses that are trapped in the mucus
• Deterioration of cells that prevent infection
• Reduction in antibody production
• The prevalence in older people of “chronic diseases such as diabetes, obesity, hypertension, chronic obstructive pulmonary disease (COPD), heart disease, and dementia” that increase inflammation in the body
• Impairment of the body responses that fight inflammation

A healthy diet and exercise may help the body maintain its immune system. Other aspects of healthy lifestyle — not smoking, drinking only in moderation, and reducing stress — can also reduce the strain we place on our immune systems.

Unfortunately, it isn’t always possible to avoid diseases that compromise the immune system. The natural process of aging also tends to impair the immune system, although the rate of impairment varies widely.

The Benefit of Vaccines

Vaccines protect against developing a disease after exposure to a virus. By imitating an infection — in this case, by imitating SARS-CoV-2 — a vaccine stimulates the body’s immune response system. Believing that it is under attack by a virus, the immune system begins to develop antibodies to fight it off. Ideally, those antibodies protect against illness if the vaccinated individual is exposed to the actual virus.

Most vaccines are made from a component of the virus, such as a protein, rather than exposing the vaccinated individual to the virus itself. For that reason, vaccines rarely trigger the infection that they guard against.

Some vaccines (such as the one that guards against meningitis) require multiple doses to become effective. Some (including tetanus shots) wear off after a period of time.

Since vaccines trigger a response to a specific virus, they might provide no protection against a similar virus. A new flu vaccination, for example, is needed each year because flu viruses tend to be different from year to year.

Developing a Vaccine Against COVID-19

Unfortunately, it takes time to develop an effective vaccine. The first step is to identify a molecule known as an antigen that acts as a target for the immune response. Identifying the antigen target typically takes two to four years.

Researchers then try to develop a vaccine that develops an immune response in animals. Since most attempts fail, that process usually takes another year or two.

When a promising vaccine is discovered, it goes through a series of clinical trials that involve testing on humans. The first trial, involving a small number of volunteers, determines whether the vaccine is safe. The second trial, involving a few hundred volunteers, determines whether the vaccine effectively produces antibodies. Questions about the best dose to administer and whether the vaccine produces short-term side effects are answered during this stage.

The third trial involves testing on several thousand volunteers. A control group that receives a placebo is compared to a test group that receives the vaccine. The two groups are compared over time to determine whether members of test group are less likely to become ill than members of the control group.

Each of the first two trials is typically completed within two years. It often takes several years to complete the testing required by the third trial, followed by another year or two of data analysis.

When Will There Be a Vaccine to Prevent COVID-19?

While many politicians and some public health experts have expressed optimism that the time frame for developing a COVID-19 vaccine can be compressed, other scientists have been more pessimistic.

Some scientists doubt that a vaccine can be developed. The SARS-CoV-2 virus is only one form of the coronavirus. At least two hundred varieties of the coronavirus produce a common cold, for which no vaccine is available.

No vaccine has ever been approved for use against previous forms of coronavirus, in part because immunity to a coronavirus seems to wane fairly quickly. At this point, scientists are uncertain whether antibodies produced by people who have been infected will guard against a reinfection. If antibodies do not offer significant or lasting protection, it isn’t clear that a vaccine will offer effective protection against COVID-19.

An unprecedented worldwide effort has nevertheless been launched to develop a safe and effective vaccine in the near future. Attempting to shortcut the process carries risks, since the safety of any new drug only becomes clear when enough time has passed for adverse reactions to develop. There would, however, be an obvious benefit to a vaccine that protects against COVID-19, even if it requires periodic booster doses to maintain immunity.

In theory, if enough people either become infected or are immunized by vaccination, the virus will not find enough new hosts to survive and will no longer pose a serious threat to public health. Whether and when that day will come is uncertain. Until it arrives, the best protection against COVID-19 is to avoid crowds, wear a mask in public, wash hands frequently, and stay away from anyone who might be infected.