COVID-19 immunity: Studies show antibodies against novel coronavirus may last only for two-six month

Nearly 8.5 million people have been reported to be COVID-19 positive in the world and over 4,56,000 have died of the disease within the past six months. Scientists all over the world are racing to find a vaccine that can save lives and halt the spread of the disease.

A vaccine helps your body generate immunity (antibodies) against a pathogen without you ever contracting the disease.

Various countries are even considering ‘immunity passports’ to allow people who have recovered from the infection to travel more freely.

However, the latest research on the subject suggests that immunity to SARS-CoV-2, the causative agent of COVID-19, may not last even a year.

Asymptomatic people show a decline in antibodies within 2-3 months

In a small study, done in China and published in the journal Nature, 37 asymptomatic patients of COVID-19 were assessed for the clinical and immunological features of the disease.

The study found that most asymptomatic people shed the virus for a median of 19 days, which was longer than that of the symptomatic group -- 14 days for those with mild symptoms. However, people who are asymptomatic do not have as strong an immune response as those who show symptoms.

The researchers also studied 37 asymptomatic and 37 symptomatic people for eight weeks after the patients were discharged from the hospital. The IgG levels declined in about 93 percent asymptomatic people and about 96.8 percent symptomatic people in the early convalescent (recovery) phase. Though the latter still had a higher number of IgG. IgG is the antibody that is responsible for long-term response against a pathogen.

About 81 percent of asymptomatic patients and 62 percent of the symptomatic ones had a reduction in neutralising antibodies. Neutralising antibodies are those that bind to the virus and stop the infection.

Immunity against common cold coronaviruses starts declining within six months

In another study done in Amsterdam, 10 people were followed up with for 35 years to study how their body reacts to coronaviruses that cause the common cold and for how long their immune system sustains antibodies against these viruses. There are about four coronaviruses that cause the common cold.

The study found that all individuals showed a significant reduction (about 50 percent) in their coronavirus antibody levels within six months and had reinfection within a year. The antibody levels dropped by about 75 percent in all people within 12 months. Half of the people had no immunity against the virus after four years.

The average age of the patients at the beginning of the study was between 27 and 40 years and by the end of the study, it was around 49 to 66 years.

The study concluded that if SARS-CoV-2 immunity also lasts for as long (since it is part of the coronavirus family and shares many characteristics), there is a high chance of reinfection among patients. However, for reinfection, a person has to be exposed to the virus again.

Also if this is the case with COVID-19 causing virus, serological testing for the infection would be useless if done a year after the infection and a vaccine for the virus may need to be given more frequently -- say, every six months to maintain sustained immunity.


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