Can We Become Immune to Covid-19?
By: Andy Chan
Tags: Health, World, Science, Healthcare, Coronavirus

Consider this: there’s a jam jar with mold on top. You scrape off the surface and now, it looks like it’s mold-free—until you realize that the jar may still have mold that continues to grow.

That’s an analogy by Dr. Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health, when asked about negative tests for coronavirus.

“A negative test is not a definitive that there is no more virus in that person,” he said in an article on the New York Times.

That has been supported by a study on JAMA, published on the follow-up of recovered patients. After conducting PT-PCR tests on the four recovered patients (who were medical professionals) after they were discharged, the test came up positive for the coronavirus despite them being asymptomatic. This could explain why there were reinfection cases in Japan and China.

Although we might get reinfected with the cold—caused by coronaviruses—the current strain that’s causing Covid-19 is vastly different in terms of epidemiology and genetic structure. Judging by the current numbers, the reinfections seem to be occasional.

For the most part, we can expect that we’ll get some form of immunity for Covid-19. However, thinking of the immunity in this one-sided manner is not enough. We must understand whether this immunity exists, and if so, how long does it last, and whether we can still spread the disease even after recovering.

Let’s tackle that one by one.

The short answer is that we’re likely to gain some form of immunity to Covid-19 after we recover. Our body’s immune system is built this way: once bitten, twice shy, and it will be poised to take on the same virus should it attack our body again. Is it safe to assume that it’s the same for the coronavirus?

First, we need to address the reinfection cases—are they isolated cases, or are they suggestions that it’s unlikely for us to be immune? Besides Japan and China, other reinfections cases also appeared in South Korea and on the Diamond Princess, the cruise ship that was moored at Yokohama port.

The most worrying one comes from Guangdong, with about 14% of patients being retested as positive. The Guangdong CDC also had no clear conclusion on why this happened.

Researchers offer varying explanations as to why there are reinfection cases. For that, testing errors are a main focus:

The over-sensitivity of the PCR diagnostic test, which may be picking up fragments of the virus. One example would be how it could detect remnants of the measles virus, despite recovered patients not shedding the infectious virus.

Throat swab likely missed the virus hiding elsewhere in the body.

False negatives where patients are being discharged too early, likely due to improper storing of swab samples.

“Excessive” testing and follow-ups on discharged cases in China might be contributing factors, according to Dr. Dale Fisher.

What about other possibilities not related to testing methodologies? Some speculate that it might be a new version of the virus (after the virus has mutated in someone else). However, the most likely explanation would be that such viruses persist at low levels in the body even after someone recovers—we see this with Zika and Ebola, which are known to stick around for months.

Hence, the current stand is that there is immunity. Some researchers have noted that patients develop a protective antibody after being cured. The term ‘reinfection’ wouldn’t be apt, but instead more of a ‘relapse’. We can look at MERS-CoV, which is a strain of the coronavirus: recovering from it gives us potential antibody response in the future (although this depends on where the virus has attacked).

Unfortunately, this is still all up for speculation. For the aforementioned protective antibody, that might only last for a short time. The U.S. CDC has no clear conclusion on the immune response to Covid-19 as well as other researchers.

With all that said, there’s still hope. A promising study appeared in medRxiv in a joint study between the University of Melbourne and Doherty Institute. It offered the first pieces of evidence of an immune response, and it lasted at least 7 days before full resolution of symptoms.

Another hope comes from the mild cases, which take up a majority proportion of the current confirmed case total. Most people who are infected by the coronavirus look like they contracted the flu. Since it’s unlikely to be fatal, these people will likely have antibodies—something that Chinese authorities are asking donations for in hopes that they could use the antibodies to treat other patients.

In sum, it’s better not to bank on the immunity.

There’s a definition of what constitutes a full recovery by the CDC. However, going back to Dr. Lipsitch’s analogy, having no symptoms can mean that we are still asymptomatic since the virus persists in our body at unknown levels (despite needing to be tested negative twice for it before being discharged).

It sounds dangerous, but it’s likely that the virus won’t be as contagious as before. A study on Macaque monkeys showed that these monkeys could not contract an infection a second time, which is a great initial study in understanding the immune response to Covid-19.

Another study also showed that we might not be infectious, even if we are shedding high levels of the coronavirus after recovery, which explains why some patients even tested positive for weeks despite recovering.

That said, it’s way too early to set any conclusion.

One of the biggest challenges right now is that the amount of extant research is still not enough for us to understand Covid-19 to its core. There is an impetus for full-scale studies of follow-up patients to understand post-recovery infection rates, and whether there is any immunity at all. For now, it’s best not to bet on our immune systems and assume the worst, while we patiently wait for treatment and vaccines to be developed.