The Path of COVID-19

It’s easy to see a mask and understand how it works. Facemasks help limit the spread of the COVID-19 by inserting a physical barrier between the virus and where it needs to go. This alone greatly reduces risks of contracting COVID-19. But what about the vaccine? How can we visualize how the vaccine works to limit serious illness, hospitalization, and death? Here’s a tour of an infected body, including what the immune system does and what the virus does, in vaccinated and unvaccinated people.

Day 1: The virus enters the body through the eyes, nose, or mouth. It begins to enter healthy cells in the lining of the nose, sinus cavity, and mouth. Right away, it begins to make copies of itself. Even at this early stage, regardless of vaccination status and before symptoms arise, the infected person could be infectious to others.

Day 2 – 5: The immune systems of vaccinated people have been provided with an early warning that the virus is coming. They can respond quickly and, potentially, illuminate the threat before it has an opportunity to cause symptoms.

Some vaccinated people may begin having symptoms at this point and can test positive for COVID-19 at this stage. Most commonly, their symptoms remain mild and the person recovers completely within a few days.

Day 5 – 14: Where the virus really wants to be is in the lungs. This is where it is best equipped to latch its spiky surface proteins on healthy cells. In fact, the lower airways have more ACE2 receptors than the rest of your respiratory tract, so COVID-19 is more likely to flourish there.

Note that the vaccine doesn’t work as well in people whose immune systems are compromised. Even though they had the vaccine, the immune system may not catch the virus until it gets further into the respiratory tract, where it can do more damage.

This is when the immune systems of people who are unvaccinated and those who are immunized but immune compromised jump into action. This group is very likely to develop a fever and a cough. Their lungs can become inflamed, which makes it difficult to breathe.

In many cases, unvaccinated and immune-compromised people remain at home and slowly get better. Some continue to have symptoms for many months.

Sometimes, people develop pneumonia, a lung infection, and may need hospital care. Some people go on to develop acute respiratory distress syndrome (ARDS). In the body’s attempt to cope with the infection, the tiny air sacs that transfer oxygen to your blood start to fill with mucous. An imaging test of the lungs would show the places where parts of the lungs are no longer getting any air. The oxygen levels in the blood fall, and the person may need a ventilator to breathe. 

The virus can also replicate in blood cells and affect the blood’s ability to work effectively. This disrupts healthy levels of critical elements like oxygen, nitrogen, iron, and others. These changes can decrease the body’s ability to transfer oxygen from the lungs into the bloodstream and from the bloodstream into other organs, which can result in harm to blood vessels, the heart, the brain, kidneys, liver, gut, eyes, and pancreas.

Beyond Day 14: A small percentage of people will not be able to recover from their COVID infection. Others will begin to feel better but may continue to feel the after effects of COVID for many months.

We don’t yet know what the long-term effects of COVID are for any group—vaccinated, unvaccinated, immune compromised, young, or old—but we can be certain that those who are vaccinated will fair better than those who are not.

Marie George, MD, FIDSA, is an infectious disease specialist at SVMC Infectious Disease and Southwestern Vermont Medical Center in Bennington.