WE have been told that the only cure for our Covid crisis is through the development of a vaccine.

Until then,working from home, bans on mass gatherings, and restrictions on whether pubs, restaurants and even hairdressers can re-open will be the “new normal”.

The pessimistic outlook – at least for the short to medium term – was laid bare by First Minister Nicola Sturgeon last week as she warned that restrictions may remain in place “for the rest of this year and maybe even beyond.”

But what if an effective vaccine is never found – or not found in time?

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Vaccines came too late for SARS or Ebola. We have never discovered a vaccine for HIV. And the annual winter flu vaccine can only ever offer patchy protection because it is based on a ‘best guess’ for which combination of strains will be in circulation each year.

One of Scotland’s most respected experts in this field – virologist Professor Hugh Pennington – told MSPs this week that he “would not be putting any money” on the Holy Grail of a Covid-19 vaccine.

Unlike measles, where people tend to develop lifelong immunity, there is no guarantee Covid-19 is behaving this way.

Earlier this month, South Korea’s health chiefs reported the puzzling – and potentially troubling – cases of 91 patients who appeared to have recovered from the infection only to test positive again later.

It is unclear exactly why this happened but a ‘relapse’ rather than a re-infection has been suggested. There is evidence the virus may lie dormant at undetectable levels in human cells before potentially ‘re-activating’.

Another explanation are false negatives. Conventional coronavirus tests can give the wrong result 20 to 30 per cent of the time, and are especially prone to error when a person is asymptomatic.

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However, concerns are such that the World Health Organisation issued a statement last Friday cautioning countries (which include the UK) against plans for an ‘immunity passport’ certifying that an individual is safe to travel or return to work having already had the virus.

“There is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection,” stated the WHO, adding that studies show some of those who have beaten the infection “have very low levels of neutralising antibodies in their blood, suggesting that cellular immunity may also be critical for recovery”.

Cellular immunity refers to an immune response where the body manufactures a type of white blood cell known as a T cell which is capable of recognising and destroying other cells infected with the virus – not just the viral pathogen itself.

This was the point Prof Pennington was alluding to when he warned MSPs that a vaccine may prove ineffective.

He said: “Many people don’t really develop very much in the way of antibodies but they recover from the infection, which might suggest that traditional vaccines are not going to be particularly effective.

“I think probably the best thing we can hope for is a vaccine or a set of vaccines which will be partially protective, and they may not work as well in the elderly because most vaccines don’t.”

It is also possible that by the time a vaccine is ready for late-stage clinical trials there will no longer be enough virus circulating to actually test it against.

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No SARS vaccine made it beyond phase I safety trials before the disease vanished in 2004, while researchers testing a possible Ebola vaccine in 2014 ran out of participants as the outbreak slowed.

SARS, the closest relative of this new coronavirus, spread to 26 countries and caused 774 deaths. But vast surveillance testing, including thermal checks at airports, prompt isolation of patients, and strict quarantine for all known contacts, succeeded in interrupting human-to-human transmission to such an extent that the disease was effectively eradicated. There have been no known cases since.

This may not work for Covid-19, however. SARS patients were most infectious when they were already visibly ill with respiratory symptoms. There was no known transmission of the disease from asymptomatic or mildly sick patients.

Covid-19, on the other hand, seems to spread more easily and transmits even before symptoms emerge. By the time patients become seriously ill, isolation will often come too late.

Other hopes rest with antivirals, which have transformed HIV treatment.

However, that too is proving elusive with the Lancet reporting today that the first randomised control trial of Ebola drug remdesivir found that it did not speed recovery in critically ill Covid patients, or reduce deaths, compared to a placebo.

However, the scientists also note that their study – based on 237 patients in Wuhan, China – had to stop early after the steep decline in cases in China meant they ran out of patients to recruit.

Ironically, the success of social distancing itself may hamper our quest for a cure.