How long does Covid-19 immunity last after infection? It's bad news

As work on a vaccine continues, many are wondering how long immunity lasts for those who have already contracted the coronavirus.

Scientists haven’t been able to provide a definitive answer as the coronavirus hasn’t been around long enough to tell.

But there are a few warning signs that don’t look good.

For starters, the European Centre for Disease Control says its best estimate is up to 52 weeks.

On its website, it states: ‘The longevity of the antibody response is still unknown, but it is known that antibodies to other coronaviruses wane over time (range: 12 – 52 weeks from the onset of symptoms) and homologous re-infections have been shown.’

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A year is an understandable frame of reference, given that it’s generally the same with mutating colds and flu – which is why we need to have flu vaccine each year.

However, over in the United States, the Centre for Disease Control (CDC) has quietly updated its own guidelines with an even more conservative estimate.

They say that an infected person may only be safe again for another three months.

According to the CDC’s website: ‘People who have tested positive for COVID-19 do not need to quarantine or get tested again for up to 3 months as long as they do not develop symptoms again.

‘People who develop symptoms again within 3 months of their first bout of COVID-19 may need to be tested again if there is no other cause identified for their symptoms.’

The reason a person’s immunity to a changing virus wears off is because the body can’t keep producing the required antibodies.

Antibodies from a vaccine may disappear from the bloodstream after about three months. However, if a virus reasserts itself, our immune system can call up a backup generator known as T cells. These reengage with the infection and start producing antibodies again. Unfortunately, it’s not known how long these T cells stick around for.

Last month, researchers at King’s College London looked into the immune response of 90 patients and healthcare workers at Guy’s and St Thomas’ NHS Trust.

Their findings seem to have pre-empted the CDC’s three-month rule.

While the analysis revealed a ‘potent’ level of antibodies in 60% of participants at the peak of their battle with coronavirus, sequential blood tests showed that only 17% retained that same level of potency three months later.

According to the research, which has not yet been peer-reviewed, immunity antibodies decrease significantly in the three months following infection, suggesting patients could be susceptible to reinfection year after year – similar to the common cold.

Lead author Dr Katie Doores told the Guardian: ‘People are producing a reasonable antibody response to the virus, but it’s waning over a short period of time and depending on how high your peak is, that determines how long the antibodies are staying.’

The research indicated that antibodies rose higher and lasted longer among patients with severe cases.

That may be because they have more virus and produce more antibodies to fight off the infection.

The results would appear to undermine any idea of pursuing ‘herd immunity’.

They would also have implications for the development of a vaccine as any protection offered may similarly wane in two to three months, meaning one shot may not be enough.

Dr Doores said infection is typically the best-case scenario to trigger an antibody response and if infection gives you antibodies which diminish in two to three months, ‘the vaccine will potentially do the same thing’.

There are currently four other types of coronavirus in circulation among the human population – including the common cold.

Professor Stuart Neil, who co-authored the study, told the Guardian that ‘one thing we know about these coronaviruses is that people can get reinfected fairly often’.

He added: ‘What that must mean is that the protective immunity people generate doesn’t last very long. It looks like Sars-Cov-2, the virus that causes Covid-19, might be falling into that pattern as well.’

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