Do those who get COVID-19 become immune to it after recovery?
As the three-week lockdown begins and all the news seems to be talking about is the novel coronavirus, many of us are wondering how long this crisis will last. Will we be out of it in a month? Will the hot summer kill it off? Will social distancing work miraculously and dramatically lower transmission?
All of these are good questions, but all that can be offered right now is educated guesses or speculation. Social distancing appears to be the best way forward - it will give the scientific community time to develop medication or a vaccine and take the strain off healthcare infrastructure and resources.
A related question is if people will get immunity from COVID-19 after contracting it. Can you get it twice? Do you become immune to it once you recover, and if so, for how long?
The promise (and risk) of herd immunity
The UK government initially wanted to rely on herd immunity to tackle the novel virus. Herd immunity is a concept claiming that if a majority of people in a population are exposed (and hence immune) to a microbe, the whole group would become immune. This would happen regardless of the presence of some susceptible people as the microbe wouldn't be able to transmit easily. The disease would still exist, but cases would be low and health infrastructure would be able to manage it.
It turns out that this approach is too risky - a study by Imperial College, London has shown that those with severe conditions would be in the millions if no protective measures are adopted, far outstripping the capabilities of health systems.
This is where the question of reinfection and immunity comes in as well. It turns out that we don’t know enough about whether people can be reinfected with COVID-19 either.
What does the evidence say?
Four other types of coronaviruses cause common colds and the flu - estimates suggest around 15 to 20% of all common cold cases. Studies on these viruses seem to suggest that an immune response is developed which can ward off infection for some time. A small, unpublished study, looked at two rhesus macaques who had recovered from COVID-19 after only showing mild symptoms. After exposing them to the virus again, it was found that they did not contract the infection.
There is limited research on SARS and MERS as well; the coronavirus strains that caused those diseases are very similar to COVID-19. It appears that those who were infected with SARS had antibodies in their blood even 15 years after the infection. However, it is not known if these are sufficient to prevent another infection. As for MERS, since it killed around 30% of those it infected, research is even scanter on reinfection. A small study showed that an immune response was seen but that antibodies fell drastically soon afterwards.
From all of the above, it appears that the body does offer some sort of immunity against influenza-like viruses. However, there is a major caveat: research seems to suggest that this immunity is short-lived.
Why could this be? For some viruses like HIV, it is because the virus evolves quickly — it can even evolve within the same person — so that it is difficult to mount an immune offensive.
To make matters more complicated, this does not seem to be the case with coronaviruses; it does not appear that they evolve nearly as rapidly as HIV. So why our bodies are not able to mount a sustained attack against this virus remains a mystery currently.
The bottom line
The evidence we have for the number of recoveries so far is encouraging - close to 110,000 have recovered and not faced complications since. For the small number who tested positive after testing negative before, it has not been established if it was faulty testing or a second wave of the infection.
Further, everyone’s immune response is different; some may develop more comprehensive immunity while others may remain susceptible after recovery.
For now, we should take solace from the fact that the vast majority — upwards of 95% — of those infected are expected to recover from the infection. Scientific inquiry and clinical trials are taking place at unprecedented rates to tackle COVID-19 and hopefully, there will be more clarity soon.
For more tips, read our article on Coronavirus.
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Updated Date: Mar 26, 2020 14:23:13 IST
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