Immunity, here we go again


Dr. Raymund W. Lo

Amid the rising number of Covid cases, people are starting to feel anxious again, if not panicking outright. Sure, there’s a definite upward trend, but we’re still not seeing the number of hospitalizations and ICU occupancy that we saw in the initial and Delta surges. The Omicron surge was milder, though it was so infectious that almost everyone I knew had Covid. That didn’t lead to a rush to hospitals, though it overloaded our testing labs, whose personnel was also hit by a proportionately large number of infections, causing some labs to close or temporarily reduce the number of samples they tested.

Today, we’re still seeing mainly Omicron circulating, and even the new variants are actually Omicron with a minor difference, the so-called sub-variants. It is expected that though one may get infected again, the immunity gained from previous infections still prevents serious disease.

A big factor is the high vaccination rate overall, especially in the urban areas, where crowding is expected. This, coupled with the huge number of cases during the Omicron wave, may have led to a semblance of herd immunity, which is what we really want.

Is this wishful thinking? Well, based on preliminary information from researchers investigating immunity from Covid vaccinations, it appears that almost all samples tested, from vaccinated persons or not, have high levels of antibodies as well as vigorous T-cell responses. Antibody levels did not appear to wane several months after vaccinations or boosters. It’s either that the vaccines are very effective in inducing prolonged immune response or that intervening infections boosted immunity, or a combination of both. But I’m getting ahead of the researchers, so I’ll let them fill in the rest when they finish up their studies.

To better understand all this jazz, we need to know the workings of our immune system better. We have innate and acquired immunity. Innate immunity is the initial defense we have against infections. The soldiers we call on for this are the neutrophils, macrophages, and natural killer cells. On contact with foreign invaders, neutrophils and natural killer cells produce substances called cytokines that damage the foreign invaders’ cell walls, causing the invader to rupture. Macrophages engulf the invaders, which are then digested by enzymes within these cells. Either way, the intruders are vanquished.

Not all invaders are recognized immediately as foreign, so the innate mechanism will not apply in all instances. This is where acquired immunity steps in, being a later development in the evolution of the immune system, since only higher organisms are equipped thus. The main actors are the T and B lymphocytes. T cells are involved in repulsing invaders: helper T cells aid B cells in producing antibodies, and cytotoxic T cells directly attack the foreign organisms in concert with the macrophages, which “educate” them by presenting bits and pieces of the organisms to them (resulting in cellular immunity). B cells, on the other hand, secrete antibodies that bind to and neutralize the virus, causing them to be attacked by the macrophages (humoral immunity).

SARS-CoV-2 (the virus that causes Covid-19) evades the innate immune system, so that we didn’t have any defenses against it when the pandemic first started. Before we could rely on our acquired immunity, we must first encounter the virus directly as an infection or indirectly through vaccines, which introduce bits and pieces of the virus as inactivated (dead) virus, fragments, or even specific genetic codes (RNA), as in the RNA vaccines.

What’s great about our immune system is that it “remembers” the encounter for a very long time by producing memory B cells, which can persist in the body in a dormant state until it encounters the virus again. Then it rapidly ramps up antibody production to high levels compared to the initial encounter, where it may take a while to build up antibody levels effective enough to combat the infection. This is true whether it’s through natural infection or vaccination. Of course, we’d rather not encounter the virus directly but should opt to get the immunity through vaccines, which are proven to be very safe and effective.

Vaccines were developed to prevent severe disease and not necessarily infections. That’s why we may have breakthrough infections, which should be milder than if we are not vaccinated. If another surge does come, we should be able to deal with it confidently by being vaccinated. So, here we go again — or not? Most probably not, though it would be best if we can ramp up vaccinations further to definitely assure us that we do have herd immunity and Covid will just be another form of colds.