What's the difference between natural and vaccine immunity against COVID-19?

October 19, 2021

Our latest analysis of data from the ZOE COVID Study shows that getting COVID before being fully vaccinated provides much more protection than natural immunity or vaccination alone. 

We chat with Mike Malim, Professor of Infectious Diseases at King’s College London, to find out more about natural and vaccine immunity, and to compare the effectiveness and safety of each approach. 

What is natural immunity from COVID-19?

When you catch SARS-CoV-2, the virus that causes COVID-19, your body triggers an immune response. This involves the production of antibodies by B cells, which fight off the infection, and activation of T-cells which attack virus-infected cells. 

After the initial infection is over, for most of us antibodies remain in the bloodstream to protect against reinfection. Our initial analysis of our ZOE contributors antibody test results, suggests that antibodies stick around for at least 450 days. Other studies show that they can stick around for six months or more

You’re also left with memory B and T-cells, which stay in the body for months or even years. These cells ‘remember’ what the virus looks like, so the immune system can swing into action quickly if you’re infected again in the future.

The effectiveness of the immune response and levels of immunity after having a COVID-19 vary widely between people. 

“We are all different, so our immune systems will be different too,” explains Professor Mike Malim from King’s College London. “Some people become very sick from COVID while others have no symptoms at all due to differences in the underlying immune response as well as a number of other characteristics, and there will also be a wide variation in immunity after infection.”

How does vaccination protect against COVID-19?

Vaccines work by training your immune system to recognise and respond to infection, without having to actually catch the disease.

The various vaccines against COVID-19 all work by delivering a small inert/harmless part of the virus into your body - usually the spike protein that makes up the viral coat - in a way that is designed to trigger a strong immune response. This is the same kind of immune response that you would get with a natural infection, but produced in a much safer and more reliable way. 

Most of the COVID vaccines that are currently in use are given in two doses, known as a ‘prime and boost’ approach.

“The first dose primes your immune system to recognise the virus and start building an immune response, while the second dose amplifies this response and helps lay down a strong immune memory to protect you in the future,” Mike explains

The ZOE COVID Study and many other research studies show that having two or more doses of a COVID-19 vaccine cuts the chances of catching COVID-19 and reduces the risk of being seriously ill or hospitalised if you do get it. We’ve also found that being vaccinated halves the risk of developing long COVID

Immunocompromised people whose immune systems don’t work optimally or are taking immune-suppressing drugs may have a weakened response to the vaccine. These people may benefit from a third jab to reinforce the effect of their first two vaccines

We do know that vaccine protection against COVID-19 can fade over time so booster jabs are now being offered to some groups including the over 50s, frontline health and care workers, and people with underlying health conditions.

Is natural immunity better than vaccination against COVID-19?

There are around 30 different proteins that make up the SARS-CoV-2 virus, while the vaccines only contain the spike protein.

“When you’re infected with the real virus, you make antibodies and T-cells against all of the viral proteins, giving a very broad but variable immune response,” says Mike. 

“The vaccines only contain the spike protein, so you’re just training the immune system to recognise that particular protein, but they’ve been designed to give a robust and reliable protective immune response.”

But although natural immunity gives broader protection against the virus, it’s not necessarily better. 

We know that it’s possible to be reinfected with COVID-19 after either vaccination or natural infection. 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. 

By contrast, an unvaccinated person with a previous COVID infection has only 65% protection against catching it again, clearly shown that if considered separately - vaccines offer greater protection against COVID-19 than natural antibodies

However, we also found that being double vaccinated on top of having previously had COVID-19 actually provided an extra protection boost

We found that two doses of the AstraZeneca vaccine plus a previous COVID infection gave 90% protection, while having COVID plus two Pfizer doses provided 95% protection.

“If you’ve already had COVID-19, that acts like the first dose of a vaccine to prime your immune system. Then the first dose of the vaccine acts as a booster and the second dose amplifies the effect again, adding up to higher protection overall,” Mike explains.

Is natural immunity safer than COVID vaccines?

Some people may feel that it is safer to develop immunity to COVID-19 by catching the virus, rather than being vaccinated, due to the reported side effects from the vaccine. However, while many unvaccinated people who catch coronavirus are only mildly sick or have no symptoms at all (asymptomatic infection), some people can fall seriously ill. 

Older people and those with underlying health conditions are more at risk of ending up in hospital with COVID-19, but even healthy younger people can become seriously ill or die from the disease. A recent study from the US showed that unvaccinated people are 11 times more likely to die of COVID-19 than those who have been vaccinated. 

We also know that up to one in 20 people with COVID-19 end up having symptoms for 12 weeks or more (long COVID), which can have a big impact on health and quality of life. And unvaccinated people can spread the virus to others, putting them at risk too. 

By contrast, large scale clinical trials and ongoing safety monitoring show that COVID vaccines are safe. 

After-effects like having a sore arm or cold-like symptoms are common after having a COVID-19 jab. However, more serious or life-threatening side effects such as allergic reactions, blood clots or heart inflammation (myocarditis) are extremely rare, as are deaths due to the vaccine (despite rumours circulating on social media). 

“We can definitely say that the safest way to become immune to COVID is to be vaccinated rather than catching the virus,” says Mike. 

“The data overwhelmingly shows that you are at far greater risk of being seriously ill, suffering long-term symptoms or dying compared with any rare side effects from vaccination.”

Does natural immunity protect against variants

The SARS-CoV-2 virus is evolving and changing, with new variants emerging all the time. Some of these, like the Delta variant, are more contagious and dangerous than previous versions. 

However, while there isn’t enough data to show whether being infected with an earlier version of the virus provides protection against newer variants, the latest studies suggest that vaccines are holding up well against most variants, including Delta. 

And researchers in the US have found that antibodies produced in response to vaccination are more likely to recognise variations in the spike protein than those made through natural infection.

“We don’t know how the virus is going to evolve in the future, but for now it’s looking like vaccines are providing good protection against the variants that are currently out there,” Mike says. 

“It’s simple to tweak the vaccines to take account of new variants as they arise, so it should be relatively easy to roll out updated vaccines in a similar way to yearly flu jabs, but because of the variability of natural immunity to virus infection, it’s hard to know how well infection with a previous variant will protect you against the next one.”

Do I need a vaccine if I’ve already had COVID?

Our research shows that getting vaccinated on top of having had COVID-19 provides extra protection. 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.

“COVID-19 is still a threat in the UK and around the world so we still need to work to reduce the number of infections,” says Mike. 

“Achieving the highest level of immunity in the greatest number of people through widespread vaccination and taking preventive measures like wearing a mask will reduce the levels of circulating virus and onward infections in the community, protecting us all and helping to bring the pandemic to an end.”

Stay safe and keep logging.

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