A large portion of people infected by the novel coronavirus never show symptoms of the disease. Earlier researchers have warned that these asymptomatic patients may a significant role in the spread of the COVID-19 disease as they could infect others without knowing that they have the virus. But some experts say a high rate of asymptomatic infections is a good thing as they may play a key role in ending the pandemic. Also Read – Russia’s COVID-19 vaccine: Dr. Fauci ‘hopes’ it is tested well
In an interview with an American daily newspaper, Monica Gandhi, an infectious-disease specialist at the University of California at San Francisco, said that more asymptomatic infections may trigger community-wide immunity or herd immunity against SARS-CoV-2, the virus that causes COVID-19. Also Read – Can your face mask really prevent spread of COVID-19 droplets? Use this test to find out
What is Herd immunity?
Some experts have been strongly advocating herd immunity as a potential weapon to fight the coronavirus pandemic. This strategy requires exposing a huge percentage of the population to the virus so that they develop immunity against the virus. This, according to the proponents of this strategy, will break the chain of transmission and help reduce the infection rates. Also Read – COVID-19 Live Updates: Cases in India surge to 21,53,010 as death toll reaches 43,379
Some experts have suggested that herd immunity can work in a country, like India, that has a high proportion of the younger population. This is because younger people have a lower risk of death and hospitalization risk due to COVID-19. Earlier it was believed that herd immunity can be achieved if around 60 per cent of the country’s population becomes resistant to the novel coronavirus. However, a study published in the journal Science in June 2020 suggested that herd immunity can be achieved with fewer people, suggesting the threshold percentage as 43% and not 60%, as estimated earlier.
However, some experts argued that even if herd immunity was achieved, there is no guarantee that antibody levels will stay the same. They cited a study that found that levels of an antibody in recovered Covid-19 patients fell sharply in 2-3 months after infection.
COVID-19 patients rely more on T cells to recover
In a study published in the journal Nature, a research team revealed that most asymptomatic COVID-19 patients can shed the virus for an average of 19 days, and thus they can play a major role in spreading the disease. The study also showed that antibodies in asymptomatic COVID-19 patients decline within 2-3 months.
The researchers found that levels of Immunoglobulin G (IgG) – antibody that protects against bacterial and viral infections – dropped in about 93 percent asymptomatic COVID-19 patients and about 96.8 percent symptomatic cases in the early recovery phase. In addition, it was found that 81 percent of asymptomatic patients and 62 percent of the symptomatic patients showed a decline in neutralising antibodies – the antibodies that bind to the virus and stop the infection.
But this and other antibody surveys didn’t focus on T cells, to which COVID-19 patients rely more upon to recover. These cells can last for years and some scientists believe are they more important in fighting off an infection.
A study on coronavirus and T cells published in the journal Cell in mid-May found that T cells present in 40-60% of the old blood samples reacted to SARS-CoV-2.
The researchers hypothesized that T cell response could have originated from previous exposure to similar viruses, such as SARS, MERS, or common cold coronaviruses.