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Covid-19 Immunity

“I have had the infection, how long will I will be immune for?”

Some recent reassuring data

What was already well known about Covid-19 immunity:

  • Within 2 weeks of infection, people infected with the virus produced antibodies to the virus 
  • The level of antibodies was greater in people
    • who had symptoms compared to those who did not have symptoms
    • People who had severe symptoms compared to those who had mild symptoms

What we didn’t know was: 

  • How long would the antibodies last for?
  • Would those antibodies protect against further infection with Covid-19? (Not all antibodies ‘neutralise’ the virus – ie they are present but do not do anything useful)

Can you get Covid-19 twice?

  • This is the flip side of the questions above: if immunity was successful  would you get a second infection?
  • There have been a few highly publicised individual cases, but it is not known if the infection cleared fully the first time.  What’s more, a few isolated cases in the media do not really answer the question.
  • Also, the question is not just can you get a second infection fairly soon after the first, but more about next year or during any future wave. 

Why didn’t we know the answers to these questions?

The answer is simple in that firstly there had been the need to wait for a reliable test for immunity and secondly, we can only know if immunity lasts for (say) 6 months when enough people have been followed up for that time – in an infection which only became widespread this spring.

What does the new research show?

Results from two studies have been made publicly available in the last couple of weeks: one from Kings College London and the other from Mt Sinai Hospital in New York.  Both are preliminary and subject to further scrutiny 

The New York study:

  • They followed 121 people who had tested positive for antibodies for 3 months
  • In 90% the antibodies were persistent and the levels stayed stable
  • The antibodies were also neutralising

The London study

  • They followed 65 people admitted to Guys and St Thomas Hospital
  • 95% developed antibodies and remained positive for 3 months and only 2 of these did not develop a neutralising response 
  • The level of neutralising antibodies declined in almost everyone after about a month 

Key things to consider about the results of research on antibody tests:

  • It is not unusual for antibody levels to fall over time following infection with any virus
  • The body has a memory for past infections so even if the level has fallen, the immune system can wake up and antibody levels can rise quickly again
  • Antibodies are not our only line of defence against a further infection 

Conclusion

  • Obviously, we cannot know now everything we want to know about immunity to Covid-19 
  • The current evidence suggests that the body’s immediate response is behaving as we would expect 
  • Inevitably it will take several more months to have a more definite answer

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