We need to discuss COVID-19 immunity these days. The reason is that there are a lot of unanswered questions.

A recent study out of King’s College in London prompted the most depressing headlines this year when they announced antibodies to COVID-19 may only last a few months. Stories then began to emerge that the hopes of a vaccine fade in light of the latest research. The headline needs clarity.

The concern is if antibodies that defend us from the disease evaporate then herd immunity is impossible to achieve. Vaccines will not work and the pandemic will never go away. While the study seems dire, immunologists shrugged it off. The reason they were less concerned requires us to review a bit of immunology.

The King’s College study only examined one side of our complex immune system. The part they studied were B-cells that bind invading virus. They examined this side because B-cell antibodies are easier to measure.

It isn’t unusual for antibodies to decline after an infection. Smallpox antibodies can decline as much as 75 percent, but still last for years. The reason is the antibody level doesn’t always need to be very high to confer immunity in some diseases. We still don’t know how much of an antibody response is needed to confer immunity to COVID-19.

The other factor is even though antibodies decline, they signal that an immune response occurred and that our immune system has a memory of the exposure. This memory engages other parts of the immune system beyond B-cell mediation. What is the other part?

One of the other sides of the immune system are T-cells. The most simplistic description of T-cells is they attack and destroy infected cells. T-cells are the first cells that are lost in HIV infection and the big problem with HIV. There is also evidence that these T-cells provide the longest and strongest immunity to COVID-19.

There is emerging evidence that family members in close contact with COVID-positive patients never mounted much of a B-cell antibody response, but mounted a larger T-cell response when T-cell mediation was tested. The most convincing study was done in France and found recovering COVID victims demonstrated strong T-cell responses with no detectable antibodies.

There is also this idea that cross immunity occurs. If someone has strong immune responses to other coronaviruses such as the common cold, then they may have some immune memory to combat COVID. This may be why children seem to be less susceptible to COVID. Their immune systems are teeming with emerging immune responses to coronaviruses that are new to their young bodies.

The research is still evolving. There is still a lot we don’t know. There are also exceptions to every one of these findings. But we need to know a minimum of things over time.

We need to understand the antibody levels needed to achieve some level of protection. If boosters are needed — fine. We are accustomed to yearly flu vaccines that are updated annually.

We also need to know the T-cell response over time. This is an issue separate to the King’s College study that is being researched. We lastly need to know what a protective profile looks like. There are other vaccines that seem to confer cross immunity. There are exposures to other viruses that seem to confer cross immunity. Age, co-morbidities and immune status are complex combinations that need to be considered when developing an immunity profile.

The CDC now says that available data suggests persons with mild COVID symptoms remain infectious for up to 10 days. Those with severe symptoms may be infectious for 20 days. Some people who have recovered seem to still shed detectable virus on testing for several months, but in concentrations that make transmission unlikely. This is why the CDC adjusted their stance to a symptom-based detection strategy for ending isolation.

The science is still evolving and there is much we still don’t know. But things are still looking bright on the horizon as well.