COVID-19 Immunity Update

Apart from the established risk factors—advanced age, obesity, and health conditions, like diabetes and heart disease—nobody knows why one person would be unaffected by COVID, while another person becomes seriously ill. Discovering how to avoid serious illness is right at the center of every important question about the disease. Everyone wants to know how people become immune and what can we do to increase the number of immune people—fast. Science is revealing something new almost daily. Here’s the latest on COVID and immunity.

Can you get COVID-19 twice?
Most scientists think that a COVID infection is similar to other coronaviruses, in regard to how long immunity is likely to last, reportedly as long as 34 months. The University of Washington published a study that reported that immunity seems to persist for at least 3 months after symptoms subside and likely longer.  At the same time, last month, scientists in Hong Kong reported that they had confirmed reinfection in a 33-year-old man who had first gotten COVID in March.  This would lead us to believe that it is possible, if uncommon, for people to be re-infected with COVID-19. It is likely that immunity could only protect against serious illness. In any case, the CDC advises people who recover from the coronavirus to behave as if they haven’t had it. They should still keep 6 feet from others, wear facemasks, and wash their hands frequently.

Can you tell if someone is immune?
Scientists are working on determining specific measurements of antibodies that would indicate when a person is immune. This would be valuable in deciding whether to return to work or school, for instance, and whether a vaccine has worked, without exposing the recipient to the virus. The difficulty is in the fact that antibodies don’t stick around all the time; they come and go, as the need arises. Someone may be pretty well immune to COVID-19, for instance, without much evidence of COVID-19 antibodies at all. At the same time, the presence of COVID-19 antibodies does not indicate complete immunity. So, the amount of neutralizing antibodies you would need to be immune to COVID-19 is still uncertain.

Then what are antibody tests for?
Some people are interested in knowing if they have been exposed to COVID-19. Antibody tests, which are available with a blood draw at SVMC’s lab and many other hospitals, can tell you if you have been exposed in the past, up until 2 weeks ago. The antibody response takes a few weeks, so people exposed in the last 2 weeks might not show any antibody activity. Maybe one day antibody tests will be able to reveal important information about immunity, but we just don’t have the baseline measurement yet.

Can convalescent plasma help?
Convalescent plasma is a part of the blood taken from someone who has recovered. It is being studied as a way to inoculate those in high-risk groups and as a treatment. It usually includes some antibodies, but like we said, it’s still really hard to know how many antibodies we need to have an effect.

How close are we to getting a vaccine?
The first large study of the safety and effectiveness of a COVID-19 vaccine started at the end of July. Thirty thousand volunteers were divided into two groups. Half received two shots of the vaccine 28 days apart and the other half received two shots of saltwater placebo. Nobody in the study, neither the patients nor the staff administering the doses, knew which they are getting or giving. They are looking to see if there are side effects, whether the vaccine works to prevent COVID entirely or decrease the severity of illness, and whether one dose is enough. Since July, two more potential vaccines have entered into the final phase of testing. The New York Times Coronavirus Vaccine Tracker is a good source of up-to-date information.

How often are we likely to need to be re-vaccinated?
As you likely know, doctors recommend getting a flu shot every year. That’s because the flu mutates very quickly. Last year’s vaccine would not be very effective against this year’s illness. Coronaviruses are much slower to mutate. It seems as if we will need to be vaccinated less often for coronavirus than for the flu.

What is herd immunity?
Herd immunity is when spread is slowed, because most people are immune. It is usually achieved when most of the population receives an effective vaccine. This is how we have managed some of the world’s killer diseases, including the measles and polio. Loosening restrictions in an aim to achieve herd immunity to COVID without a vaccine could relate to tremendous loss of life. Most public health and infectious disease experts are against an attempt at herd immunity without a vaccine. For now, our best defense is widespread and consistent masking, distancing, and handwashing. 

How long will COVID be with us?
Even once we get a vaccine, it is likely to be mostly, but not entirely, effective. So COVID-19 is likely to be with us for a very long time. I would estimate its impact on humanity to last in the hundreds of years. The good news is that with a vaccine, COVID-19 is likely to be far less serious and far less deadly in the future.

Marie George, MD, FIDSA, of SVMC Infectious Disease, is an infectious disease specialist.