Covid-19 Immunity Re-infection

Hong Kong report a man catching Covid-19 twice: no cause for concern

The Journal of Infectious Diseases yesterday issued a press release highlighting a report they had accepted for publication.  In that report a young Hong Kong male who had definite but mild Covid-19 in March, was tested positive 10 days ago for a different strain of the virus-the first such case globally. The Hong Kong scientists suggested this should cause concern about immunity following infection, although other scientists have been reassuring.  What issues does this report raise?

A note about the public release of this report

  • The full scientific report is not, at the time of writing, available on the Journal’s website, so the details cannot be explored
  • This is not acceptable: if reports are going to be released to the public, then the full report must be available for scrutiny.
  • Note that in CNN’s news bar they falsely mentioned the case was a woman!

What is the significance of a single case report?

  • There have been 24 million cases of Covid-19 documented worldwide.
  • There have been cases suggesting people being ill twice but this is the first to show definitely a new infection.
  • Of course, other second cases may have arisen and not identified, but if there had been a significant number we would know.
  • The fact that this is the first is reassuring.

Should we worry that the second infection was a different strain?

  • There are new strains of the virus emerging all the time.  
  • As said before in this blog, that is normal for a virus but interestingly Covid-19 shows less tendency to mutate than other viruses
  • If it hadn’t been a separate strain, identified by more stringent genetic testing than is usually done, then it would not have been possible definitively to say this was a new infection

Does this case prove that immunity from a first infection would not protect against a different strain?

  • It is already well known (and discussed in this blog on 28 July) that immunity can fall over time especially in cases of mild infection
  • What is not known is whether, despite falling immunity, when faced with a new infection, the body’s antibody and other immune protection mechanisms would still come into play
  • For sure, the more different the second strain of a virus, the greater the possibility that the existing immunity might not full give protection
  • BUT the antibody response may still give some protection across strains

The Hong Kong case is interesting because….

  • The young man had no symptoms the second time
  • Although he was positive on swab testing the second time confirming the presence of the virus, he may have had an antibody response which protected him from any serious consequences
  • Thus (and not wishing to make conclusions on one case) perhaps it is reassuring that he did not become ill

Any issues about vaccines?

  • Not really, as the vaccines are designed to be active against the spike protein
  • There is no evidence yet that the spike proteins vary in different strains 


  • Nothing is certain about this virus (perhaps justifying this blog!!!)
  • However, the case should not have received the publicity it did.