Does a COVID infection guarantee protective antibodies?

November 9, 2021

Our latest analysis of data from the ZOE COVID Study shows that one in five ZOE Study participants who tested positive for COVID didn’t go on to have detectable anti-N antibodies afterwards. 

Here’s what we discovered.

How do we test for COVID antibodies?

When you’re infected with the virus that causes COVID-19, SAR-CoV-2, your immune system responds in a number of different ways. 

One important response is to produce antibodies - these are special molecules in your body that recognise the virus and help to get rid of it, and provide protection against future infections.

One way of telling whether someone has been infected with COVID-19 is to look for the presence of virus-fighting antibodies in their blood. 

There are two types of antibodies that we can test for:

  • Anti-N tests look for antibodies that recognise a molecule inside the SARS-CoV-2 virus called the nucleocapsid (N). Anti- N antibodies are only produced if you’ve actually been infected with COVID-19 (natural infection).
  • Anti-S tests look for antibodies against the spike protein (S) on the surface of the virus; these antibodies can be present after both a natural infection and a vaccine. This is because COVID vaccines are based on the spike protein. 

Find out more about antibody tests in our blog post.

Does catching COVID give you immunity?

Between April and August 2021 we invited thousands of ZOE COVID Study contributors who had logged a positive COVID test in the app to do an anti-N antibody test at home. Here’s the full details of the tests we used. 

Out of 8,193 contributors who tested positive, 6,609 (80.67%) had a positive anti-N antibody test result - so they had Anti-N antibodies. 

While it’s good news that four out of five people infected with COVID-19 ended up with protective antibodies afterwards, it means that one in five did not, and they could be at greater risk of getting infected again.

Who gets antibodies after a COVID infection?

Looking more closely at the data, we saw that people who had a greater number of symptoms while they were ill with COVID - particularly the ‘classic three’ symptoms of cough, fever and loss of smell (anosmia) -  were more likely to have gained antibodies against the virus.

In contrast, people with one or more health issues associated with an underlying condition (known as comorbidities) were less likely to have antibodies after being infected, as well as people who currently smoke. However, our research can not link smoking directly to reduce immune response and it might be that there are other negative health behaviours involved here that impact the immune system.

There was no link between age, sex/gender or social deprivation with the likelihood of having antibodies afterwards.

How long do COVID antibodies last?

We’ve previously found that vaccine-induced protection from COVID starts to fade after a number of months

In this new research we found that people still had anti-N antibodies at least 9 months after infection, suggesting that protection through natural infection might be longer lasting than vaccine-induced immunity.

However, we’ve also discovered that protection through natural immunity is less effective overall than vaccination, so we would always recommend you get vaccinated as soon as you’re eligible.

Our data shows that two doses of the AstraZeneca vaccine give 71% protection against infection, while two doses of the Pfizer vaccine provide 87% protection. But an unvaccinated person with a previous COVID infection has only 65% protection against catching it again.

However, being vaccinated on top of having had COVID provides even better protection - two doses of the AstraZeneca vaccine plus a previous COVID infection give 90% protection, while having COVID plus two Pfizer doses provide 95% protection.

What’s the best way to protect yourself from COVID?

Together with our previous findings comparing vaccine-induced with natural immunity, these results show that while being infected with COVID-19 can provide some level of antibody protection, it’s not guaranteed for everyone, and the level of protection is lower with natural immunity. 

Professor Tim Spector, lead scientist on the ZOE COVID Study, says,

 “It’s interesting to observe that, unlike vaccination, it’s not just older, frailer or overweight adults who gain least protection from a previous infection, but rather anyone with poorer overall health and those who smoke. Our data show that the best way to protect yourself and others from COVID-19, even if you have had the virus previously, is to have 2 doses of vaccine and the booster when offered, and to take sensible precautions such as wearing a mask. Not only does this cut your chances of catching the virus and becoming seriously ill, it also reduces the likelihood of passing it on to others who may be more vulnerable.”

If you’ve had an antibody test or a COVID vaccine (including booster jabs), don’t forget to log it in the ZOE COVID Study app, along with your daily health reports. It only takes a minute but you’ll be contributing to vital research to help us bring the pandemic to an end. 

Stay safe and keep logging.

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