The COVID-19 pandemic has been the topic of intense research and has turned the world’s attention towards the immune system of our bodies. In the early phase of this pandemic, researchers discovered that patients who recovered from the infection did not carry any antibodies against it. Later, it was observed that people who developed antibodies against Coronavirus appeared to lose them again after two to three months. This got worldwide researchers exploring the mechanism of antibodies developed in Coronavirus infected individuals. In this article, we will talk about whether a person can get re-infected with Coronavirus. Let us first understand how our immune system reacts to Coronavirus.
How does our immune system react to Coronavirus?
When a virus enters the body, an infection occurs. It will progress to a disease only if the virus increases in number and attacks the immune system.
Our immune system has two types of response against any pathogens.
- Innate (natural) immunity: This acts as the body’s first line of defence and natural barriers against disease-causing pathogens. The skin, hairs in our nose, mucous membrane, flushing action of tears, and the acid in our stomachs are part of our innate immune system. Though it reacts quickly to an infection, it fails to recognize all the pathogens.
- Adaptive (acquired) immunity: This forms the second line of defence of our body which develops over a lifetime of contact with pathogens and vaccines. Adaptive immunity is a slow process and can take several days before the T cells and B cells get activated. When the Coronavirus invades, these T cells and B cells start making antibodies (IgG and IgM) specific to the virus and then destroy them. Antibodies are proteins highly specific to a particular infection produced by the immune system.
How soon are antibodies produced after an initial Coronavirus infection?
The World Health Organization (WHO) has cautioned against the notion that antibodies provide permanent immunity. Some government bodies suggested that the antibodies (IgG and IgM) detection to COVID-19, could serve as the basis for an “immunity passport” or “risk-free certificate”. However, these suggestions were rejected by the WHO stating that currently there is no evidence to prove that the antibodies present in people who have recovered from Coronavirus can protect them from a second infection.
However, the Centres for Disease Control and Prevention (CDC) has revealed that antibodies against the Coronavirus develop within 1-3 weeks after the infection. It also suggested that a patient infected with Coronavirus (SARS-CoV-2) is unlikely to be re-infected for at least 3 months or more after they recover.
Why do some people test positive for COVID-19 again?
In April 2020, South Korea reported that 116 people who already recovered from COVID-19, tested positive for Coronavirus again. The Korea Centres for Disease Control and Prevention (KCDC) then issued an explanation stating that the Coronavirus may have been reactivated rather than the patients being re-infected. Scientists believe that traces of Coronavirus can be found in the patient’s body even after they are free from symptoms but that does not mean that they are still infectious.
What does further research about antibodies and COVID-19 say?
Studies are being conducted across the world on antibodies developed against viruses, including the Coronavirus. The findings are as follows:
- Singapore: The results of a study published in the Nature research journal showed that 23 patients who recovered from severe acute respiratory syndrome (SARS) 17 years ago, still carried antibodies (virus-specific memory T cells) and displayed cross-immunity to the Coronavirus.
- USA: The findings published in the Science Immunology showed that of the ten Coronavirus infected people, all were able to generate COVID-specific T cells and B cells. Besides this, two of the uninfected people already had developed T cells against COVID-19. This may have been possible because of cross-reactivity where these two people would have been infected with the common cold coronaviruses in the past.
- Rhesus macaque monkey study: A group of Chinese researchers reported that they had infected six rhesus monkeys and allowed them to recover. After 28 days, four of them were re-infected again with the Coronavirus but none became sick again. This study showed that the monkey’s immune system developed antibodies that shielded them from a second infection.
- Less mutation time of Coronavirus: Based on the current data, it can be concluded that the Coronavirus (SARS-CoV-2) mutates lesser than (25 times/year) the flu or influenza virus (50 times/year). This means that any innate (natural) immunity or vaccine developed later would offer more lasting protection. This gives us hope for the potential development of effective long-lasting vaccines against the Coronavirus. Besides this, even if a person gets infected with Coronavirus again, the second infection might be milder than the first one.
What does ‘herd immunity’ for COVID-19 mean?
Herd immunity or community immunity occurs when any larger part of the community (herd) becomes immune to any disease, making the spread of the infection unlikely. For attaining herd immunity, the percentage of the population that is immune to the infection must exceed the un-infected population, known as the herd immunity threshold. Experts have estimated that at least 70% population of the USA (more than 200 million people) would have to recover from Coronavirus infection to halt the pandemic.
In India, it started with ‘zero immunity’ and now Delhi has 23.5% of its population who recovered in July 2020 which indicates they are immune to Coronavirus. According to the Scientific Advisory Committee of the National Institute of Epidemiology (India), once we reach the herd immunity level (50%-60%), the pandemic may settle down. Once this level is achieved, COVID-19 may stop showing its epidemic nature and there won’t be any need for quarantine.
Until a vaccine is available against COVID-19, our immune systems will need to adapt to this virus. A healthy lifestyle can help an individual’s immune system to be in the best shape and enhance its ability to tackle the virus. However, it is better to prevent the virus entry in the first place by wearing a mask or face shield, getting our home and objects disinfected, following hand hygiene and social distancing. Most studies mentioned in this article suggest that people who got infected with the Coronavirus may have developed antibodies and gained some immunity. However, more research is required to confirm whether the upcoming vaccination or herd immunity will be able to produce the antibodies which would last long for a lifetime.