Once infected with coronavirus, is it possible to be infected a second time? Do antibodies made against coronavirus give us complete protection? Or can it protect you from being attacked a second time? All these questions have been in everyone’s mind for so long. Although experts say that once infected, the chances of being infected a second time are very low, but there is no specific evidence to support this. This time, the first evidence of this was found in the blood test of a group of prisoners who went out to fish from Seattle, USA.
A research paper on this has been published this week in the preprint server MedrixV. The world-renowned science journal Nature has published a report on it. In this study, 122 fishermen were selected. Before going fishing, both RT-PCR and antibody tests were done by collecting samples from 120 members of the 122-member team. But unfortunately, the coronavirus infection started among the passengers soon after crossing the sea. After returning to shore, tests showed that 104 people, or 85 percent, were infected with the coronavirus. Genome sequencing of the coronavirus obtained from these patients proved that the virus was transmitted from one person to another.
The most important information that was found was that the three passengers who tested positive for antibodies before crossing the sea and who had neutralizing antibodies in their bodies to neutralize the virus later did not become infected. They were asymptomatic and their RT-PCR test results also came back negative. Since 75 percent of passengers are infected with the coronavirus, these three are not infected. So it was assumed that they were protected because they had antibodies against the coronavirus in their body.
Although the data are very basic, there are two very important aspects of this study. First, this study demonstrates that antibodies made against coronavirus can protect a patient from a second infection. Again, this information indirectly sheds light on the effectiveness of the coronavirus vaccine.
Coronavirus patient Divya has recovered but her RT-PCR result is not negative at all, even after two weeks have passed! Surely you can hear many such cases among your acquaintances? The explanation is important. Because, in most countries, those who are in quarantine after being infected with coronavirus, under the current rules, must be tested negative at least twice within 24 hours before being declared coronavirus-free. This is to ensure that the patient does not spread the disease among others.
In that case, the patient is forced to stay in quarantine even after many days of recovery. The same problem is with the patients being treated in the hospital. The patient is not going to be released even after he recovers. The bed is not going to be emptied to give others a chance. But the question is, does being RT-PCR test positive mean that the patient is infected? Recent research suggests that this is changing. But before we talk about this, let’s take a look at the principles of RT-PCR.
Reverse transcriptase polymerase chain reaction or RT-PCR is a type of nucleic acid amplification test. This means that a copy-DNA of a virus is first created in a test tube by following the RNA genome. It is then expected to identify a specific part of that copy-DNA, artificially multiplying it by the number. In the case of coronavirus, RT-PCR tests are performed on the patient’s respiratory sample to identify whether the patient is infected by identifying the virus’s RNA.
The chemical reaction, called PCR, is carried out by raising and lowering the temperature step by step. Each test usually has 40 such steps or cycles. The faster or shorter the cycle, the more likely it is that the RNA of the virus will be detected. And the unit to measure it is the bicycle threshold or CT value. The higher the CT value, the lower the sample virus or its RNA. So the PCR method is semi-quantitative and this test gives us some idea about how many viruses there are in our respiratory system or how many viruses there are, although not exactly accurate. But even then, CT value or viral load or number of viruses are not usually disclosed during test reporting.
Test positive or test negative, this is how it is reported. This is because it is not possible to determine the number of virus-infected human cells in a respiratory sample. Again, since test standards vary from place to place, qualitative results are given, not quantitative ones.
One thing you need to know is that RT-PCR only identifies the RNA of the virus, not the whole virus. So whether the virus in our respiratory tract is active or inactive, the results will be positive if the virus has RNA. To know whether the virus is active or inactive, it is necessary to cultivate the virus in the laboratory. But culturing the virus is quite difficult and time consuming. Moreover, coronavirus culture requires BSL-3 level facility. Culture methods are not used nowadays for routine diagnosis of the disease. Instead, the patient is considered to be infected with the coronavirus as soon as the RNA of the virus is detected through RT-PCR tests.
But whether a person infected with the coronavirus will spread the disease to others depends on the number of viruses active in the patient’s respiratory tract. The number of viruses is usually highest for two to three days after the onset of symptoms, and then if the RT PCR is tested, the CT value is much stronger, such as 25 or below. After the patient has a normally healthy body, the virus gradually fails to reproduce due to the body’s immune system, and its numbers continue to decline. At the same time, when RT-PCR test is done, it is seen that as the city value gradually increases, it becomes negative at some point.
The problem is that in some patients, after complete recovery, the results of the RT-PCR test become poor. It takes a long time to be negative. The question is, are these patients still contagious? To answer this question, some recent studies have looked at RT-PCR as well as virus culture. As can be seen, the number of active viruses decreases as the RT-PCR city value increases and no active virus has been found in the culture since the city value rose to 33 or above.
Similar information is coming from several countries including France and Canada. Meanwhile, 285 patients were tested in South Korea. After they recovered, the RT-PCR test again yielded positive results. In none of them was the active virus detected by culture. However, out of 690 patients who came in contact with these patients, 3 were infected with coronavirus. According to the South Korean Center for Disease Control and Prevention.
Based on these studies and data, even if the RT-PCR is not negative but the city value is 33 or above, some countries are deciding to send corona patients home from quarantine or hospital discharge. There is a need for more research in this regard and the World Health Organization has not yet issued any new guidelines in this regard.