Immunity to coronaviruses may only last six months, says study

Immunity to reinfection from human coronaviruses may last only six months, according to a study from the University of Amsterdam.

It casts doubt over the practicality of introducing "immunity passports", which some governments want to issue to COVID-19 survivors on the assumption they can't be reinfected and are free to help the economy get back on its feet.

The study monitored 10 men over 35 years to determine antibody levels following infection for any of the four seasonal human coronaviruses.

These men, then aged 27 to 40-year old, were tested at either three or six months intervals.

Researchers found that there was an "alarmingly short duration of protective immunity to coronaviruses" with scientists noting "frequent reinfections at 12 months post-infection and substantial reduction in antibody levels as soon as 6 months post-infection".

They stressed that the four strains of human coronaviruses are "biologically dissimilar" and "have little in common, apart from causing the common cold".

"Still, they all seem to induce a short-lasting immunity with rapid loss of antibodies. This may well be a general denominator for human coronaviruses.

"If SARS-CoV-2 will behave like a seasonal coronavirus in the future, a similar pattern may be expected," they went on.

They thus cast aspersions on the idea, floated by some governments, to introduce so-called "immunity passports" to people who contracted and recovered from the deadly COVID-19 virus that would allow them to travel and relax some social distancing measures.

"As protective immunity may be lost by 6 months post-infection, the prospect of reaching functional herd immunity by natural infection seems very unlikely," they warned.

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Britain's Health Secretary Matt Hancock announced last week that the government is working on a "system of certifications" to enable people who have recovered to resume certain activities.

He added that antibody tests that would deliver results in 20 minutes are currently being trialled on 4,000 patients and that they could be rolled out nationwide if effective.

"It's that knowing you have these antibodies will help us understand more in the future if you are at lower risk of catching coronavirus, of dying from coronavirus and of transmitting coronavirus," he said.

In Italy, a large-scale study into the seroprevalence — the level of a pathogen in the population — of COVID-19 launched on Monday.

The Ministry of Health and the Red Cross will test blood samples from 150,000 people from across 2,000 municipalities for antibodies.

People with antibodies will be asked to submit to a COVID-19 nasal swab to determine whether they currently have the virus and their level of contagiousness.

There is currently no known treatment or cure for the novel coronavirus, which has claimed more than 345,000 lives worldwide, according to a tally by the Johns Hopkins University.

According to the World Health Organization (WHO), 10 candidate vaccines are currently in clinical evaluation and a further 114 are in pre-clinical evaluation.

The University of Oxford announced last week that it was moving into Phase II of its vaccine and that more than 10,000 adults and children would be enrolled.