Immunity & COVID-19

Understanding immunity to COVID-19, induced by both natural infection and through vaccination, is key to our ability
to exit the current pandemic.
In this report, you will find the answers to key questions around what we know and don’t know about immunity to the virus SARS-CoV-2, which causes the disease, COVID-19. This includes the effectiveness of the immune response, how to measure and track immunity, the benefits of vaccine-mediated immunity, and the longevity of any immunity conferred. We have sought to make the subject matter relevant to both the public policy discussions that are ongoing and those that will arise as the pandemic situation begins to change over the next few months.
It is important to say that there are differing degrees of immunity. Different individuals will create different immune responses to invasive pathogens, and the case of the SARS-CoV-2 virus is no exception. 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 (so-called ‘sterilising’ immunity), while others will make antibodies* and be protected from the disease COVID-19, but may still be infected with the SARS-CoV-2 virus and transmit it to others (‘protective’ immunity).
Immunity can be difficult to measure. The best marker currently is neutralising antibodies*, which have been shown to persist in some individuals up to 8 months after original infection. While immunity can also be measured by looking at memory immune cells, methods for doing this at scale are not currently available. Immunity can wane over time and this can lead to the small chance of reinfection. Exactly how long immunity following COVID-19 lasts will need a longer time to determine.
Vaccine-mediated immunity is preferable and safer than naturally acquired immunity. While clinical trials recorded the ability of the vaccines to protect from COVID-19 disease, questions remain around whether the vaccines being administered currently will prevent people from being able to carry and transmit the SARS-CoV-2 virus. Currently not enough time has elapsed between the vaccines first being administered in humans and the present time for durability of vaccine-induced immunity to be determined, but this is the subject of ongoing phase 3 vaccine studies.
The answers to all these questions will have a profound impact on the policy decisions that the Government makes. Questions over how immunity can be measured, how long immunity lasts and the reliability of such tests can undermine the usefulness of ‘vaccine passports’, and whether the vaccine stops the spread of the SARS-CoV-2 virus to others or simply stops the person who has been vaccinated from contracting the disease, COVID-19, will be vital to finding our way out of this pandemic. The longevity of immunity conferred by a vaccine will determine whether there will be need for an annual COVID-19 vaccination programme, like that currently carried out for flu.
With so many key policy issues resting on issues of COVID-19 immunity, it is integral to the country’s future that we immediately implement a robust and widespread immune monitoring programme to understand in detail the immunity conferred through vaccination in different individuals. It is also crucial that we ensure proper surveillance of viral variance at a global scale and through this the ability of any variants to escape vaccine-mediated immunity. With the UK being an international leader in the rollout of COVID-19 vaccines, we can lead the world in immune monitoring protocols that will allow us to emerge from this pandemic more safely and quickly. This is an opportunity that we should seize with both hands.
This report aims to summarise what we know, what we do not, about immunity to COVID-19, and to provide research recommendations. An asterisk (*) denotes words that appear in the glossary (Annexe 7).