Emerging clinical research on COVID-19 shows there are at least five types or severities of SARS-CoV-2 infections: asymptomatic, mild, moderate, severe and critical. Mild symptoms of COVID-19 include cough, sore throat, muscle ache, myalgia, fatigue or headache.
In general, having an infection without any symptoms is common, says experts.
Following is a Q&A on asymptomatic cases and the risk of reinfections:
Q: How is it possible that people can test positive and have no symptoms?
Experts point to research that antibodies, natural fighters that neutralise disease-causing agents (bacteria, viruses and foreign substances in the blood), are constantly on the prowl for pathogens.
William Petri, a professor of medicine and microbiology at the University of Virginia who specialises in infectious diseases, explained many infections are fought off by the body — without the person even knowing it.
For example, in children checked for infection by the parasite Cryptosporidia, one of the major causes of diarrhoea, almost half of those with infections showed no symptoms at all, according to Clinical Infectious Diseases.
In the case of the flu, estimates vary from 5 per cent to 25 per cent of infections occur with no symptoms, according to report in Epidemiology.
WHAT IS ASYMPTOMATIC AND PRE-SYMPTOMATIC?The World Health Organization (WHO) defines asymptomatic cases as those who don’t show symptoms but have been confirmed infected through a lab test. WHO notes there are few reports of truly asymptomatic cases.
The incubation period, or the time a person takes to show symptoms after getting infected, is the pre-symptomatic phase, the WHO says. Carriers can infect others during this period.
Health experts are not yet sure whether asymptomatic or pre-symptomatic cases are infectious. Some say data so far suggests those cases are probably equally likely to be able to spread infection.
The WHO agrees that pre-symptomatic carriers are infectious, and adds that there is also a possibility – although little evidence so far — that people who are asymptomatic may also transmit the virus. The WHO had said in early April that there had been no documented asymptomatic transmissions.
In most cases, symptoms are actually a side effect of fighting off an infection. Normally, it takes a little time for the immune system to kick in its defenses, Dr Petri said, who termed some cases as “pre-symptomatic”, rather than “asymptomatic”.
The severity classifications of coronavirus cases are being adhered to by clinicians in Dubai, under a system established by the Dubai COVID-19 Command Control Centre to monitor and predict the spread of the coronavirus disease.
Under this scheme, cumulative numbers of infections, recoveries, and critical cases across Dubai are tracked closely, according to Dr Amer Ahmad Sharif, chairman of Dubai COVID-19 CCC and vice chancellor of the Mohammed Bin Rashid University of Medicine and Health Sciences (MBRU). The control centre is working on the data analytics with Smart Dubai.
Q: I have recovered from the coronavirus, can I get re-infected?
No extensive studies had been done confirming or denying COVID-19 reinfections cases in humans. There’s one done on monkeys, and it shows reinfection is not possible.
However, the World Health Organisation (WHO), citing current research, stated there’s “no evidence” that recovered COVID-19 patients who have antibodies cannot be reinfected.
In other words, the presence of antibodies in one’s system does not mean automatic protection for a recovered patient from a second coronavirus infection.
The UN agency also warned member states against issuing “immunity passports” or “risk-free certificates” to people who have been infected as their accuracy could not be guaranteed.
The WHO added the practice of issuing “immunity passports” may raise the risk of continued spread as people who have recovered may ignore advice about taking standard precautions, like social distancing, the agency added.
The agency’s warning came after Chile recently stated it would begin handing out “health passports” to people deemed to have recovered from the illness.
Q: What do current studies show about COVID-19 re-infection?
There’s no SARS-CoV-2 reinfection studies on humans yet. One study was done on monkeys, with a “pre-print” version of the results published. It shows that monkeys who had been “re-challenged” with the same coronavirus strain cannot be reinfected while antibodies are present.
Note, however, that the study was conducted only on four rhesus monkeys, a rather small subject size. Moreover, the study’s results are preliminary and had been peer-reviewed yet.
Other experts, however, believe those who had been infected (as shown by the presence of antibodies) and recovered are “somewhat protected”.
Martin Hibberd, of the London School of Hygiene and Tropical Medicine (LSHTM), London, UK, was quoted in The Lancet as saying: “I think the presence of antibodies is a reasonable indication that an individual is at least somewhat protected.”
Q: How long does the immunity last?
There’s no critical mass of scientific data currently available confirming the length of time that an immunity lasts for COVID-19 recovered patients. The reinfection study on monkeys cited above, was conducted within only short period of less than two months.
So even if it shows reinfection of the same strain is not possible, it offers no proof that re-infection by another strain is possible — or not. At this point, it’s not possible to determine how long if the immunity following recovery due to limited research.
Dr Hibberd, however, stated: “Even if that protection lasts a short while, it is still more likely to be a period of years rather than months.”
Q: What’s the reinfection record of other viral diseases?
The Lancet study pointed out that there were not enough previous cases of either SARS or MERS to draw conclusions about reinfection — and there is not much data on the common cold, either.
Q: What are the upsides and downsides of antibody tests?
A study published in The Lancet on Mary 29, 2020, states that antibody tests are useful to a certain extent, but the study also highlighted the limits of antibody “serology” for COVID-19.
There are a number of reasons for this limitation.
One, is that the information provided by antibody tests on an individual level is not specific to COVID-19, but rather a general reaction to a pathogen, which may not necessarily be coronavirus.
Second, there’s a high rate false negative test results using rapid antibody test kits — in some cases up to 30%. This results in a false sense of health, and raises the risk of a “negative” patient actually spreading the infection.
False positives, on the other hand, undermine coronavirus antibody tests.
The results (of an rapid antibody test) cannot tell you whether you are currently infected with SARS-CoV-2, nor whether you can infect others. If the test is administered too soon after the infection, there might not be detectable antibodies (although if you are in week 3 of the illness, an antibody test might be better than the RT-PCR test)
– The Lancet
Q: When I test positive in a rapid antibody test, after my initial infection, does that mean I’m immune from COVID-19? And, if so, can I go at ease on social distancing rules?
Most experts can only guess, or infer, that infection with SARS-CoV-2 will “probably” confer a degree of immunity.
However, The Lancet study states it does not follow that the presence of antibodies automatically implies or guarantees immunity.
NHS England’s medical director Stephen Powis stated (on May 20, 2020): “We would not want people to think just because you test positive for the antibody that it necessarily means that you can do something different in terms of social distancing, in the way you behave”.
Q: What’s the role of the antibody test in determining reinfection risks?
As the antibody tests are rolled out, researchers will be able to observe whether individuals previously infected with SARS-CoV-2 can be re-infected and what form this re-infection takes.
A patient’s second bout of COVID-19 is likely to be less severe than their first one, some clinicians speculate.
“It could be that in few months’ time, we will know how long the antibodies last, whether we need to be re-testing people and, if so, at what intervals”, Dr Hibberd added. “In the meantime, positive test results could be used as a risk assessment tool.”
Q: Where do antibody tests stand now and how much?
Numerous antibody tests – many of them are quite cheap, some for $3 each – are being offered by a number of manufacturers.
There risks of false positive and false negative test, with these unlicensed kits.
“We do not want people thinking they are immune to the disease when they are not,” said Anne Wyllie, of the Yale School of Public Health, adding that the US market has been “flooded” with antibody tests that have not been approved by the US Food and Drug Administration (FDA).
Another word of caution from NHS England’s medical director Stephen Powis (issued on May 20): “I would caution against using any tests that might be made available without knowing quite how good those tests are.”
Q: How does a rapid antibody test work?
Users prick their fingers to acquire a blood sample, which is then sent to the laboratory for analysis, or an on-site minilab, could yield results.
The rapid antibody test is the second type of test which aims to detect antibodies against the virus causing COVID-19. These antibodies are produced by the immune system several days after infection with the virus. A positive result in a rapid antibody test indicates a previous infection.
The rapid antibody test, however, has not been universally adopted as a diagnostic method until now.
Due to the problems associated with it, the World Health Organisation (WHO) has recommended limiting its use to epidemiological monitoring in surveys, research and epidemiological studies.
Q: What is the best test for COVID-19?
To determine whether an individual is currently infected with SARS-CoV-2 requires RT-PCR (reverse transcription polymerase chain reaction) testing. This was made available soon after the virus had been sequenced in January, 2020.
Q: What triggered the “re-infection” reports?
One trigger for supposed cases of “reinfection” came from a report of the Korean Centers for Disease Control and Prevention. It showed samples from “reinfected” patients don’t have infectious viruses.
Science News reported that the findings suggest that the diagnostic tests are picking up on the genetic material from non-infectious, or dead, viruses.
Researchers explained that the lack of infectious virus particles means these people are, in fact, not currently infected and henceforth cannot transmit the coronavirus to others.