- A new study suggests that there is a surge in the immunity of everyone who receives the first dose of an mRNA vaccine, including those who have previously had a SARS-CoV-2 infection.
- However, only people who had never had a SARS-CoV-2 infection seemed to benefit from the second dose.
- Scientists have not only tracked antibody responses to vaccination, but also the creation of memory B cells, which provide longer lasting immunity against infection.
- People who experienced particularly negative side effects from the vaccine – such as fever, headache, and muscle pain – had stronger immune responses.
Clinical trials of Moderna and Pfizer COVID-19 vaccines have shown that they are very effective in preventing SARS-CoV-2 infections.
Both injections are mRNA vaccines. This is a new technology that uses strands of genetic material called messenger RNA to provide the body’s own cells with instructions to make proteins from the virus.
Although these isolated viral proteins are harmless, they elicit an immune response that provides protection against subsequent infection by the virus itself.
Previous studies of how the immune system responds to COVID-19 mRNA vaccines have primarily focused on the production of antibodies capable of neutralizing the SARS-CoV-2 virus. However, this is only part of the story.
In response to infection or vaccination, the body produces not only antibodies, but also long-lived immune cells called memory B cells.
If the number of neutralizing antibodies in the bloodstream decreases and they do not fight off a new infection, memory B cells can scale up to produce more antibody-producing cells.
Memory B cells are also crucial for generating variations on existing antibodies that can neutralize emerging strains of a virus. This is done through a process known as somatic hypermutation.
Once a person recovers from a SARS-CoV-2 infection, their antibodies and memory B cells can provide protection against reinfection for at least 8 months.
However, researchers know much less about the ability of mRNA vaccines to stimulate the production of memory B cells and the flexible and longer lasting immunity against the new strains they can confer.
“Memory B cells are a powerful predictor of future antibody responses, which is why it is essential to measure B cell responses to these vaccines,” says Professor E. John Wherry, Ph.D., director of the Penn Institute for Immunology in the Perelman School of Medicine at the University of Pennsylvania in Philadelphia.
“This effort to examine memory B cells is important for understanding long-term protection and the ability to respond to variants,” he adds.
It is also not known whether a person who has recovered from COVID-19 needs both doses of the vaccine to achieve optimal immunity against reinfection.
If these people only need one dose, healthcare professionals could, in theory, use the reserve doses to protect others if vaccine stocks are limited.
All participants were about to receive their first dose of Pfizer or Moderna vaccine.
The researchers took blood samples from them at the start of the study, 2 weeks after their first dose, on the day of their second dose, and 1 week after their second dose.
Antibody levels in SARS-CoV-2 naive participants did not peak until after the second dose.
This was especially true for antibodies capable of neutralizing the B.1.351 strain of the virus, which is a “variant of concern” that scientists first identified in South Africa.
This was also the case for neutralizing antibodies to the D614G mutation, which the researchers say makes the virus more transmissible.
In addition, two key lines of memory B cells did not peak in the blood of naive SARS-CoV-2 participants until after their second dose.
These are the B cells that remember the spike protein, which allows the virus to enter cells, and the receptor binding domain, which is the part of the spike protein that binds to a receptor on cells. .
However, in people who had recovered from a previous infection with SARS-CoV-2, their antibody and memory B-cell responses peaked after the first dose of the vaccine.
Research now appears in the journal Scientific immunology.
The results may prove useful for the development of future vaccination strategies.
“We need to make sure that people have the most powerful memory B cell responses available,” says Professor Wherry.
“If circulating antibodies decline over time, our data suggests that durable memory B cells could provide a rapid source of protection against re-exposure to COVID-19, including its variants,” he adds.
Interestingly, the bodies of naive SARS-CoV-2 participants who experienced more serious side effects after vaccination – such as fever, headache, fatigue, and muscle pain – tended to develop stronger antibody responses.
Professor Wherry explains:
“Everyone has good answers to vaccines. They work to protect people from COVID-19. But for those who may worry about side effects, they aren’t necessarily a bad thing – they can actually be an indicator of an even better immune response.
Authors point out that their lab study was unable to prove that people who have recovered from COVID-19 only need one dose of an mRNA vaccine to optimize their immunity to future infections. by SARS-CoV-2.
A large clinical trial would be needed to assess the effectiveness of one or two doses against real infections.
Another limitation of the study was that people who recovered from the infection did not require hospitalization. Therefore, the results may not be applicable to people who suffer from more serious infections.
Finally, it should be noted that all participants were in good health. Conditions that increase a person’s vulnerability to COVID-19 – such as high blood pressure, obesity, and diabetes – can also affect their immune response to vaccination.
Researchers will expand their research to find out how long different types of immunity last after vaccination.
They also study the responses of T cells, which are the other wing of the body’s adaptive immune response to pathogens such as viruses.
For live updates on the latest developments regarding the novel coronavirus and COVID-19, click here.