People with Covid 'not fully protected against reinfection'

People who have already caught the coronavirus ‘are not fully protected against reinfection’, study warns

  • Researchers studied 3,000 US Marines aged 18-20 for signs of Covid infection 
  • They found 10% previously infected with Covid had been later reinfected 
  • Covid antibodies provide some protection in young adults from reinfection 
  • They do not guarantee immunity, suggesting vaccination against COVID-19 remains crucial even in those previously infected with the virus

Young people that have previously been infected with coronavirus will not be fully protected against reinfection, according to a new study.

Researchers from Icahn School of Medicine at Mount Sinai analysed data on more than 3,000 healthy members of the US Marine Corps aged 18 to 20.

They found that about 10 per cent of those involved in the study that had been previously infected with Covid-19 had become reinfected.

Study authors warned that despite previous infection and the presence of antibodies, vaccination is still necessary to boost immune responses, prevent reinfection and reduce transmission.

They added that young people should take up the vaccine whenever possible.

Young people that have previously been infected with coronavirus will not be fully protected against reinfection, according to a new study

People ‘could be reinfected with Covid every two to four years’ as virus mutates into new variants 

Mutant variants of coronavirus could reinfect people every two to four years, a top scientist has warned.

Paul Hunter, professor of medicine at the University of East Anglia, said it was normal for future strains to emerge and that they will not necessarily cause serious illness.

But he warned that ‘it’s very difficult to predict’ because ‘you never really know what each new variant will do’.

Government advisers are already finding that vaccines are less effective on existing variants, including as much as 30 per cent less effective on the South African one.

Highly-transmissible mutations first detected in Kent and Brazil are designated ‘variants of concern’ and also driving a third wave across Europe.

Professor Hunter stressed that many new variants are not cause for concern, but would have to be monitored to ensure it does not derail the roadmap for lifting lockdown.

According to the observational study carried out between May and November 2020, 19 of 189 Marines infected with Covid caught the virus again. 

This was compared with new infections in 50% (1,079 out of 2,247) of participants who had not previously been infected with the virus.

Although the study was in young, fit, mostly male recruits, the researchers believe the risk of reinfection will apply to many young people.

However, the exact rates of reinfection will not be applicable in other settings, because of the crowded living conditions on a military base.

The team said the close personal contact required for basic training was likely to contribute to a higher overall infection rate than elsewhere.

For example, a study of four million people in Denmark found that the risk of infection was five times higher in people who had not had the disease before.

But researchers found that only 0.65% of those who had had Covid-19 during Denmark’s first wave tested positive again during the second wave, compared with 3.3% of people who tested positive after initially being negative.

In addition, a preprint study including British healthcare workers found that those who had not been previously infected had a five times higher risk of being infected than people who had a past infection.

Professor Stuart Sealfon, senior author of the study, said it is important to remember that, despite a prior infection, young people can catch the virus again. 

‘Immunity is not guaranteed by past infection, and vaccinations that provide additional protection are still needed for those who have had Covid-19.’

Recruits who tested positive for a second infection during the study were isolated and researchers followed up with additional testing.

Levels of neutralising antibodies were also taken from subsequently infected participants who were not reinfected during the study period.

Of the 2,346 participants followed long enough for this analysis, 189 were seropositive and 2,247 were seronegative at the start of the study.

Across both groups, there were 1,098 (45%) new infections during the study and of the recruits who were seronegative, 1,079 (48%) became infected.

The authors studied reinfected and not infected participants’ antibody responses to understand why these reinfections occurred.

They found that, among the seropositive group, participants who became reinfected had lower antibody levels against the virus than those who did not.

When they compared new infections, they found that patients who had the virus before and became reinfected had about 10 times less of the virus in their system than someone who was infected for the first time.

This suggests some reinfected individuals could still be able to transmit the virus, but the authors noted this will need further investigation.

They found that about 10 per cent of those involved in the study that had been previously infected with Covid-19 had become reinfected

In the study, most new cases were asymptomatic – 84% (16 out of 19 participants) in the seropositive group, and 68% (732 out of 1,079) in the seronegative group – or had mild symptoms, and none were admitted to hospital.

The authors noted some limitations to the study, including that it is likely to have underestimated the risk of reinfection in previously infected individuals.

This is because it does not account for people with very low antibody levels following their past infection.

They were also unable to determine how seropositive recruits contracted their previous infection and confirm it by PCR test or determine how severe it was and what symptoms they had.

They found that, among the seropositive group, participants who became reinfected had lower antibody levels against the virus than those who did not

Researchers said they also could have missed detectable infections that occurred between the PCR testing every two weeks during the study, published in The Lancet Respiratory Medicine journal. 

‘Although antibodies induced by initial infection are largely protective, they do not guarantee effective SARS-CoV-2 neutralisation activity or immunity against subsequent infection’, the study mentioned.

A separate study published in the Lancet in March found that the majority of people who have had COVID-19 are protected from getting it again for at least six months but older people are more prone to reinfection than younger people.

As few as 2 per cent of positive results from lateral flow results are accurate, Matt Hancock adviser says in leaked emails after Boris Johnson called on nation to take them twice a week

As few as two per cent of positive Covid lateral flow test results taken in low prevalence areas are accurate, an adviser to Matt Hancock has warned.

In emails, leaked to the Guardian, senior strategist Ben Dyson is said to have warned health department colleagues about the unreliability of lateral flow test results.

Mr Dyson, who is an executive director of strategy at the health department and one of health secretary Matt Hancock’s advisers, reportedly raised feared that the reliability of positive results could be as low as two per cent in certain areas.

The email was reportedly sent on April 9, four days after Boris Johnson announced a multi-billion pound plan for a mass-testing drive in the UK – which would see Britons test themselves twice a week with lateral flow tests.

According to the Guardian, Mr Dyson said in his email: ‘As of today, someone who gets a positive LFD result in (say) London has at best a 25 per cent chance of it being a true positive, but if it is a self-reported test potentially as low as 10 per cent (on an optimistic assumption about specificity) or as low as 2 per cent (on a more pessimistic assumption).

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