Home Immunity Reviews | Covid vaccine policy should take into account “hybrid immunity”

Reviews | Covid vaccine policy should take into account “hybrid immunity”



As a doctor in a Covid-19 care unit, I celebrate vaccines as one of medicine’s greatest triumphs. They offer extraordinary protection against serious illness and death and are the best option in the world to resume a more normal life. As a scientist and principal investigator for a study on Covid-19 immunity, I have also come to appreciate the importance of the so-called natural immunity acquired by those who have had Covid-19, and the power of “l ‘hybrid immunity’ – the protection gained when these people are also vaccinated.

While the concept of natural immunity has often been misused by those opposed to vaccination mandates, public health officials and scientists should be open to the evidence. Research, including my team’s study of the immune responses of nearly 2,150 healthcare workers in Sweden after infection with SARS-CoV-2 – the virus that causes Covid-19 – and vaccination, suggests that the protection obtained against infection is long lasting and can be greatly enhanced by a single dose of the Covid-19 vaccine.

This information should be taken into account in immunization policies. For example, should vaccination warrants and passports make exceptions or accommodations for people who have already had Covid-19? Should children who have been infected receive two doses of the vaccine when they could be well protected by just one? These are just a few of the questions scientists and policy makers should be asking themselves.

Infection, like vaccination, causes the immune system to fight the disease. In either case, the antibodies are produced by so-called memory B cells, which help prevent future infection. The memory T cells then support the production of antibodies and control the infection by killing the infected cells.

But the immunity provided by infection compared to vaccination differs in many ways. For example, a Covid-19 vaccine teaches the immune system to target a specific part of the virus, the spike protein, over a few hours or days. When people are infected with SARS-CoV-2, their immune system is exposed to the whole virus for several days or weeks. This gives the immune system considerable time to build up a full defense if the infected person survives. These distinctions translate into broader immunity for those infected compared to those vaccinated.

Conversation of opinion
Questions around the Covid-19 vaccine and its deployment.

The immune cells that a person develops after infection also continue to evolve to become more powerful and diverse. Once a previously infected person is also vaccinated against Covid-19, these cells are awakened and they begin to generate antibodies that can help fight new variants. This is what scientists call hybrid immunity.

No one should ever try to make Covid-19 get the protection of so-called natural immunity. Even a mild infection carries the risk of serious, longer-term health problems.

But there are contexts in which a person’s previous Covid-19 infection needs to be considered for vaccination policies, and some countries are already doing this.

At the end of September, 14 European countries, including France, Germany, Italy and Spain, recommended that people without underlying health problems who have already been infected receive a dose of a vaccine (for vaccines with a two-dose schedule). Israel is offering a temporary “green pass,” an immunity passport, to people who have recovered from Covid-19 in the past six months, regardless of their vaccination status. The European Union allows travel between member states if citizens or residents have a positive PCR test showing they have recovered from Covid-19 within the past 180 days. Britain is also accepting proof of a positive Covid-19 test result within 180 days for its Covid Pass.

But these are exceptions; many countries still recommend two doses of the Covid-19 vaccine for everyone and issue vaccination warrants that make no exceptions for people who have already had Covid-19.

The rationale for these general recommendations is that not everyone develops a strong immune response after infection. And the data shows that while so-called natural immunity can last for a long time – perhaps up to a year – the length varies depending on factors such as a person’s age, medical conditions, and the severity of the disease. .

But studies also suggest that otherwise healthy people who previously had Covid-19 show equal or greater levels of immune responses after one dose of the vaccine compared to people with two doses and no previous infections. People with hybrid immunity also don’t seem to gain much more immunity from a second dose, suggesting that second injections may not be necessary for them (although future boosters may still be needed). .

A more adapted approach may be interesting to consider for certain groups.

Children, for example, are much less likely than adults to become seriously ill from Covid-19. And there is a risk, although rare, of vaccine-related myocarditis (inflammation of the heart) which is more common in young people, especially boys, after their second dose of an mRNA vaccine. Some countries like Norway and Great Britain only give one dose of Pfizer vaccine to children aged 12 to 15 to avoid potential risks like myocarditis from the second dose.

But giving all children a single dose comes with concerns that a single dose will not provide strong, long-lasting protection. Whether or not a child has had Covid-19 is not part of those vaccination decisions – and should be.

If scientists and policymakers consider the power of hybrid immunity, it is reasonable to recommend a single dose for children without serious health problems who have had Covid-19. If parents are unsure whether their children have ever been infected, antibody tests may be done when they receive their first dose of the vaccine. While these tests may not detect all children who have had Covid-19, they would detect most, and only children without a confirmed infection could be called back for a second dose. Such an approach could also help free up doses for the many other countries with low vaccine supplies and at-risk adults who have not been vaccinated. The approach should at least be considered for further study.

There are other reasons for ignoring natural immunity in decisions about vaccination. Adding antibody tests to determine who had Covid-19 to an already logistically difficult vaccine deployment can be difficult. In countries like the United States with deep political divisions over vaccines, a ‘one size fits all’ strategy may be preferable to a more tailored approach which could create confusion, generate anti-vaccine sentiment and interfere with passport issuance. vaccine.

But the recognition of a previous infection as an important contributor to immunity should not be confused with an anti-vaccination stance. The effectiveness of vaccines against Covid-19 is not questioned. But a full course of immunization isn’t the only way to protect people from Covid-19. Open discussions on the risks and benefits of personalized approaches for groups like children are worth having.

Charlotte Thålin is the principal investigator of a study on immunity to Covid-19 at the Karolinska Institute in Stockholm, where she is also a doctor at Danderyd Hospital.

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