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Immunity and COVID-19: What do we know so far?

A new policy report from the British Society for Immunology explores what we do and don’t know about immunity to SARS-CoV-2, the virus which causes COVID-19. Understanding immunity induced by both natural infection and through vaccination, is key in our ability to exit the current pandemic. The information in this review was put together by our expert group.

Here is an accessible Q&A for a public audience summarising the main points from the report and what the immunology research priorities should be for scientists working in this area. You can also read the full report and the news story accompanying the report launch on our website.

For more information about COVID-19 vaccinations, we have published a free ‘Guide to vaccinations for COVID-19’ for the public, aimed at providing easy to understand information on how vaccines work and answering common questions.


Immunity to SARS-CoV-2, the virus that causes COVID-19, following natural infection

What does immunity to SARS-CoV-2 look like?

Your immune system has many ways to fight off an infection. One of the ways is for specialised immune cells called B cells to create proteins called antibodies. These antibodies stick to the virus to mark it for destruction by the immune system or prevent it from entering your cells. Another way the immune system fights off infection is by activating other specialised immune cells called T cells, which can attack and kill any of your cells that are infected with the virus. These specific B cells, their antibodies and T cells will remain in the body as memory cells after the infection has gone.

About 90% of people who have encountered SARS-CoV-2 and mounted an immune response will have antibodies to it in their blood and these can be tested for.  

The initial immune response appears to be linked with severity of disease, with those people who experience a more severe illness having a stronger immune response. However, in some cases the immune response itself can be damaging to your tissues or it induces excessive inflammation. We need to be able to distinguish between a protective immune response and a damaging immune response and studies looking into this are ongoing. 

Does everyone make the same immune response to SARS-CoV-2?

No. The immune response varies hugely between different people. Some people create a very effective immune response, so they will not get sick again from SARS-CoV-2 and will not pass the virus to anyone else. Others will make antibodies and be protected from getting sick with COVID-19 but may still be infected with the SARS-CoV-2 virus and transmit it to others. Most people who are infected with SARS-CoV-2 make some form of immune response but whether this is effective at preventing reinfection in the future is not easy to determine.

We need to identity which immune markers (antibodies, T cells etc.) predict who is immune to COVID-19 and who is susceptible to either mild or severe disease. These markers will allow us to identify people who are at particular risk.

Are there any other factors that will have an impact on the level of immunity generated?

There are many factors that have an impact on the level of immunity generated, including age. Older people are less likely to make effective immune responses to infection, while there is evidence that children have a reduced antibody response to SARS-CoV-2.

Additionally, those people with weakened immune systems because of certain diseases or medication, will not be able to make as good an immune response as young healthy people.

How long does immunity to SARS-CoV-2 last?

As SARS-CoV-2 has only been around for a year, it is difficult to fully understand how long immunity lasts after infection. Current evidence suggests that antibody concentrations in the blood of people who have been infected do decline over time but can persist in some people for at least 8 months, and possibly longer, after infection. It has also been found that B and T cells that recognise SARS-CoV-2 are also present in the blood 8 months after infection. Exactly how long immunity will last will need a longer time to be determined but research into this is ongoing. For this reason, we do not yet know enough about the duration of protection to issue ‘immunity passports’.

Can I become infected with SARS-CoV-2 twice?

It is possible to be reinfected with SARS-CoV-2, but this is extremely rare. Reinfection will depend on both the level of immunity a person gains from the first infection and the level of exposure to the virus due to social and working environments.

Immunity to SARS-CoV-2 following vaccination

What sort of protection does COVID-19 vaccination give me?

So far, we know that the three currently approved COVID-19 vaccinations in the UK (BioNTech/Pfizer, Moderna, Oxford-AstraZeneca) prevent people getting sick with COVID-19. We don’t yet know if any of these vaccines stop people becoming infected with SARS-CoV-2 and whether they prevent you from spreading the virus. We know that the vaccines reduce your chance of getting ill with COVID-19 but we don’t know if you can still be carrying the virus, even if you don’t have any symptoms and feel well. This could mean that vaccinated people still spread the virus unknowingly. Continued monitoring of clinical trial participants and those who have received the vaccines will reveal this in the future. Therefore, even after you’ve been vaccinated, it is important to keep following other measures to prevent the spread of the virus including mask wearing, social distancing and hand hygiene.

In the same way that natural infection varies widely between different people, the immune response to a vaccine may be different in some people. For example, older people and immunocompromised people may not make as strong an immune response to a vaccine compared with young healthy people. This will continue to be evaluated but vaccination is still recommended in these groups of people as they are at higher risk of severe COVID-19. We need to understand how well the vaccines work in different groups of people so that guidance can be adapted to make sure that the right vaccines are directed to the right patients.  

Will the vaccines still work against the new variants of the virus?

It is not yet known if all the vaccines will protect against all the new variants of the SARS-CoV-2 virus. However, knowledge of the immune system leads us to assume that vaccines will still be effective against minor variations of the virus. The approved vaccines in the UK were tested in clinical trials before the new variants were widespread, so we don’t have a lot of information yet on their efficacy against the variants but research is ongoing to address this. The virus variants will need to be monitored and evaluated to assess if current vaccines will continue to provide protection against these new variants. We may need to tweak the vaccines to induce an appropriate immune response to new variants.

How long will the vaccine protect me from getting ill with COVID-19?

It is not yet known how long immunity to COVID-19 from vaccines will last. It is suggested that immunity will last for at least a year so we may therefore need to revaccinate people at high risk of severe disease every year, much like we do for the annual flu vaccine. Research into how long immunity lasts after COVID-19 vaccination is ongoing.

Is it better to gain immunity naturally or through vaccination?

The only way to get naturally acquired immunity would be through infection with the SARS-CoV-2 virus that causes the disease. When infected, you become infectious to other people around you and can spread the disease. Infection poses a serious risk to your health, potentially making you very ill and causing long-term health effects. Vaccination allows you to build up immunity in a safe and controlled way without becoming ill with COVID-19 and passing it to others. Vaccines decrease your chance of developing COVID-19 and reduce how unwell you become if infected.

Vaccines are capable of stimulating a better immune response than the natural infection. It is hoped that vaccines for COVID-19 will provide protective immunity for at least as long as natural immunity or longer, which is why you will still be offered the vaccine even if you’ve had COVID-19 in the past. It is likely that, in a significant proportion of the population, the vaccine will induce more effective and longer lasting immunity than that induced by natural infection. Hence it is recommended that everyone take the vaccine so that if your immunity after disease is absent or low, it can be boosted.

 

Written by Erika Aquino, BSI Public Engagement Manager

You can download the full report here. To find out more about other BSI work on coronavirus, please visit our 'Connecting on Coronavirus' website section

The British Society for Immunology has also published a free ‘Guide to vaccinations for COVID-19’ for the public, aimed at providing easy to understand information on how vaccines work and answering common questions. It can be downloaded for free from our website.