Omicron, immunity and breakthrough infections: why reinfection with Covid-19

Omicron Vaccine

The large-scale vaccination of the new crown vaccine continued to be promoted. The global new crown vaccine vaccination exceeded 10 billion doses, and the booster doses were rapidly popularized. However, the epidemic situation continued and repeated, especially after the emergence of the most contagious Omicron variant, which promoted the spread of the epidemic. Infections and deaths from Covid-19 continue to rise.

Partial answers to this question, and widespread concern, are the rise in cases of reinfection after full vaccination and recovery from infection when 60% of the world’s population has been at least partially vaccinated with at least one of the more than 20 approved vaccines.

Why is re-infection after being fully vaccinated, or once infected and cured? What is a breakthrough infection?

How does immunity arise?

Whether it’s vaccination or the production of antibodies from an infection, the result is that the body becomes immune to the virus. Will I be reinfected if I am immune to the new crown?

To answer this question, we must first understand what immunity is and how it arises.

The immune system is the body’s defense system against infection and consists of two parts: the innate immune response and the adaptive immune response. Once a virus or germ is found to have invaded the body, the immune system’s first response is to try to annihilate the foreign enemy, including the release of chemicals that cause inflammation and snowballs that can destroy infected cells.

The innate immune response does not learn and does not target any specific virus, and therefore does not develop immunity to the new coronavirus.

Adaptive immune responses are key — including cells that produce targeted antibodies that can stick to the virus and block it, as well as T cells that recognize the virus and target infected cells, the cellular response.

Research shows that it takes about 10 days to develop antibodies against the new coronavirus, and the most severely ill patients develop the strongest immune responses.

The efficacy of the new crown vaccine will gradually weaken after about half a year of vaccination, but the degree of protection is still high

How long can immunity last?

If the adaptive immune response is strong enough, it may leave a lasting memory of the infection, providing immune protection in the future. Whether an adequate adaptive immune response occurs in mildly or asymptomatically infected individuals is not well understood.

The novel coronavirus hasn’t been around long enough to know how long immunity will last.

However, a study by Public Health England (PHE) in the second half of 2021 suggested that most people infected with Covid-19 could avoid re-infection with the virus for at least five months.

However, some people get reinfected, and even if they don’t have symptoms, they carry high levels of the virus in their nose and mouth, which can be passed on to others.

Research from King’s College London has shown that levels of antibodies that kill the coronavirus have fallen over the three-month study period.

But even if the antibodies are gone, the cells that make them (called B cells) may still be there. There are still traces of B cells 90 years after the 1918 influenza pandemic.

If the new coronavirus is similar, the second infection will be milder than the first.

What happens to T cells, in the long run, is unclear, and the effect on T cells is still being studied. It is worth mentioning that T cells against the original SARS (Severe Acute Respiratory Syndrome) were discovered only 17 years later.

If you refer to other viral infections that cause similar symptoms, such as the common cold, immune memory is short-lived and can be infected multiple times in a year.

The results of a study published by Imperial College London in December 2021show that the Omicron variant is largely able to evade immunity from past infections or two doses of vaccination, and the risk of re-infection with Omicron is delta. 5.4 times. This level of immune evasion means that past infections may provide only 19% protection against reinfection with Omicron.

The study found the risk of developing symptoms of Omicron infection two weeks or more after the second dose of the vaccine and two or more weeks after the booster dose (AstraZeneca and Pfizer vaccines) compared to Delta significantly increased.

  • Will the common

perhaps. Laboratory tests have shown that some T cells made by people to fight SARS or the common cold coronavirus can also fight the new coronavirus. How common this is and how much protection it offers is still unknown.

  • Has anyone been infected twice?

Experts say reinfection is possible but uncommon, and larger studies are needed to determine what causes it.

A study in Hong Kong showed a young, healthy man who recovered from the virus but was reinfected more than four months later. The researchers proved by sequencing the viral genome that he was infected twice because of the different strains of the virus.

Early reports said someone had been infected with the new crown multiple times in a short period, and it was later discovered that the test was wrong.

  • Can I be immune if I have antibodies?

Can not guarantee. Although some antibodies can be found in almost every patient, there are differences in how many and how strong.

Neutralizing antibodies are antibodies that stick to the coronavirus and prevent it from infecting other cells. A study of 175 recovered patients in China showed that 30% had very low levels of neutralizing antibodies.

In addition, people who are protected by antibody immunity can still carry the virus and transmit it to others.

  • What about immunity from vaccination?

Experts recommend that even people who have been infected and recovered should be vaccinated because natural immunity may be boosted.

Variants of the new coronavirus are also an important reason – vaccines can provide a considerable degree of immune protection against mutant strains, and the immunity of antibodies produced by previous infections to different mutant strains is not clear.

The efficacy of the new crown vaccine will gradually weaken after about half a year of vaccination, but the degree of protection is still high

What is a breakthrough infection?

Infections following a full dose of the vaccine are called breakthrough infections.

The main purpose of vaccination is to effectively prevent infection, severe illness, and death, but no vaccine can provide 100% immune protection.

In addition to the weakening of vaccine efficacy over time, immune evasion and weakened immune protection caused by virus variants are also major causes, including the two mutant strains currently dominating the global epidemic – Omicron and Delta. ).

The data show that the immune protection provided by the new crown vaccine is significantly weakened 4-6 months after the completion of vaccination, and the cases of breakthrough infections and antibody attenuation have increased.

Regarding breakthrough infections, scientists can currently confirm two things: 1) Compared with people who are not vaccinated and infected with the new coronavirus, people who develop a breakthrough infection after a full dose of vaccination are less likely to become severely ill, hospitalized, or die. much less sexual; 2) a person with A vaccine breakthrough infection may be contagious.

According to the centers for Disease Control and Prevention (CDC), vaccinated people are 8 times less likely to contract Covid-19 and 25 times less likely to be seriously hospitalized or die than non-vaccinated people.

There are already figures in the UK showing a breakthrough infection rate of 1 in every 500 people vaccinated with full doses.

It is important to note that a significant portion of the current statistics come from the earliest vaccinated groups, which in many countries are the elderly and people with underlying medical conditions who have relatively low autoimmunity and where the vaccines stimulate The immune mechanism of the vaccine is weak, and the efficacy of the vaccine begins to weaken at the earliest. In addition, the threat of mutant strains must be considered.

All of these factors could push up the breakthrough case numbers for this group.

What factors contribute to the increase in breakthrough infections?

According to research results published by scholars from the University of East Anglia (University of East Anglia) School of Medicine in the United Kingdom, four main factors affect the effectiveness of vaccines, or that may push up the risk of breakthrough infections: vaccine type, time to complete vaccination, variation Virus strains, and the autoimmune system.

Vaccine type – determines the relative risk reduction rate (RRR, relative risk difference); RRR measures the risk of infection in the unvaccinated versus the risk of infection after vaccination. UK clinical data shows that several major vaccines reduce the risk of infection by 95% for Pfizer, 94% for Moderna, 70% for AstraZeneca, and 66% for Johnson & Johnson. Other data show that if the interval between two doses of AstraZeneca is extended, the infection risk reduction rate will increase to 81%.

Variant strains — this is an important variable. The original version of the virus is used in the development of vaccines, whether and to what extent the mutant strains will weaken the vaccine efficacy, and the degree of immune evasion of different mutant strains against different vaccines vary.

Ryan, a WHO expert, said in early December 2021 that the existing vaccine still has the immune effect of preventing severe illness against Omicron, although this latest variant has a partial immune escape from the Pfizer vaccine. He said there was no indication that Omicron would be better at immune evasion than other variants. World Health Organization data show that the latest dominant mutant strain Omicron has immune evasion against several major vaccines

Preliminary data from Public HealthEngland showed that the Alpha variant reduced the risk of infection by the Pfizer vaccine from 95% to 93%, and the Delta variant reduced it to 88%. The data from the COVID Symptom Study was similar: the odds of becoming ill with the Delta variant decreased by 87% within 2-4 weeks after completing two doses of the Pfizer vaccine, and 77% after 4-5 months.

Autoimmune system – one of the key factors in determining the level of infection risk. The strength of autoimmunity is directly related to age and underlying health conditions, as well as to the degree to which autoimmune mechanisms are stimulated after vaccination and the rate of decline in vaccine efficacy.

image caption,

Immunity at 5 months (dark) after two doses of AstraZeneca and Pfizer vaccines compared to 14 days after an additional booster dose (Pfizer). Immunity here refers to the degree of protection provided against illness and death requiring hospitalization. UK Health Safety Agency (UKHSA ) data

The protective efficacy of the vaccine diminishes over time. This has been generally recognized, and more and more countries have begun to implement vaccination booster programs.

Another issue that currently needs to accumulate more data is the efficacy of the vaccine against the long-term symptoms of the new crown “long new crown”.

A U.S. study of patients with breakthrough infections published in the journal Nature shows that vaccination may cut the risk of “long-term new crown” by up to half, or have no effect at all. This data helps explain why COVID-19 symptoms persist long after acute infection.

Why Booster Vaccinations?

A booster dose is also often referred to as a “third dose” because most vaccinations now require two doses, but a “third dose” is not the same as a mix-and-match vaccine, although there is some overlap. The latter refers more to an already vaccinated vaccine followed by another vaccine to increase immune protection, as well as other forms of mashup.

Sheena Cruickshank, professor of biomedicine at the University of Manchester, believes that before answering the question of whether to give a booster, it is necessary to the purpose of the vaccination and understand how the vaccine provides protection.

The initial rationale for vaccination boosters was that vaccine efficacy would diminish over time, and subsequent data from multiple channels have shown that boosters can significantly improve immune protection.

The UK’s Joint Committee on Vaccinations and Immunisation (JCVI) recommends a “third shot” with the main purpose of maximizing the prevention of hospitalizations and deaths from Covid-19 and reducing the number of infections in adults.

The committee said the decision was based on an assessment of the country’s latest epidemiology of COVID-19, mathematical modeling, vaccine safety and vaccine efficacy data, and immunological research data, as well as factors such as the ability to implement mass vaccination programs and vaccine supply.

The UK booster vaccinations mainly use the mRNA vaccines of Pfizer and Moderna, regardless of which vaccine has been used before, the AstraZeneca vaccine can be used due to drug contraindications or other health reasons. The US currently approves Pfizer, Moderna, and Janssen/Johnson & Johnson as boosters.

Kelukoshankwrote on the academic exchange website The Conversation that the main purpose of vaccination is to prevent viral infection from causing severe disease or death. The immune protection provided by vaccines consists of three parts: antibodies, T cells, and immune memory.

Improve immune protection?

Antibodies are just one measure of an effective immune response. Two other core components of immune protection: virus-killing T lymphocytes and immune memory; only immune memory can activate the autoimmune system to automatically recognize and rapidly produce T lymphocytes, and antibody-producing B cells.

The study showed no decline in T cells and immune memory.

One explanation, according to Krukoshank, is that some people have fewer antibodies over time, not enough to completely prevent infection, but still enough to kill the invading virus. That is, vaccines can lessen the damage from the virus or reduce symptoms.

There are data to prove that the vaccine is still highly effective in preventing severe illness or death, the main goal of vaccination, and can last for several months.

Real-time data from Israel shows that after four months of vaccination in the 40-59 age group, the protection rate of severe new crowns requiring hospitalization was 98%, and it dropped to 94% after six months. It’s 91% and 86%.

In addition, people over 60 who received a second dose of the vaccine in March 2021 were 1.6 times more protected than those who received two doses in January, but data from other age groups make it difficult to draw such a clear judgment; the vast majority of Most people who received the Moderna vaccine had functional antibodies that continued to work six months later, but the resistance to the beta variant waned.

Data from the UK and US so far support this view.

Vaccinated people are susceptible to infection and transmission of the world’s most important mutant strain delta

According to a study published on medrxiv.org, a medical professional exchange website, the protection provided by the Pfizer vaccine dropped from 96% to 84% four months after vaccination.

The website brings together unpeer-evaluated data and research results for peer exchange, reference, and evaluation.

Mutant strains that are more infectious and virulent, such as delta, lambda, etc., are also one of the main driving forces behind the “third shot” proposition.

Data from the CDC and other sources show that the delta strain is twice as infectious as the original strain, but the infectious period is shortened in vaccinated people. Two Israeli studies showed that the third dose of Pfizer significantly improved immunity against infections and severe illness in people 60 years and older. Other studies by Pfizer and Moderna have come to similar conclusions.

Current vaccines mainly target the spike protein that covers the surface of the new coronavirus.

What are the arguments against boosters?

The main argument against the “third needle” is that it does not have enough data to support it, and it is more out of a “preventive” mentality.

Oksana Pyzik, a senior research fellow at UCL, told the BBC there was no evidence boosters were effective or necessary.

“There is currently no data to suggest that immune protection is waning, but early data suggest that protection against mild infections is decreasing, not involving severe disease,” she said.

British researchers found that the protection provided by two doses of Pfizer and AstraZeneca began to wane after 6 months, but it did not mean that the vaccine was ineffective. In fact, the vaccine still provided highly effective protection, including immunity against the delta strain. According to Zoe Coviddata from the UK’s new crown information aggregation website, the protection provided by two doses of Pfizer fell from 88% after one month to 74% after 5-6 months. Immune protection with the AstraZeneca vaccine dropped from 77% to 67% within 4- 5 months of vaccination.

Professor Adam Finn, the UK government’s new crown vaccine adviser, said it was normal and to be expected that the efficacy of the vaccine gradually weakened. He believes that vaccination for immune protection is a must. But whether all people need boosters is another question.

One opinion is that now many people who have been infected with the new coronavirus, have also been vaccinated, have more immunity, and the effect is similar to the booster.

The new crown vaccine can effectively prevent severe illness, but it cannot ensure that you will not be infected with the new crown.

What are the uncertainties?

British scientists acknowledge that there are still some uncertainties surrounding vaccine boosters, including:

  • How long does the second-dose vaccination for non-COVID-19 high-risk groups last for immune protection against hospitalization and severe death;
  • How long the enhanced protection obtained by the elderly after receiving the booster will last, whether it will last until the fall and winter of 2022 and whether it will prevent future waves of infection;
  • The emergence of new mutant strains of concern and their potential impact on vaccine effectiveness;
  • Are there long-term effects of very rare side effects of the vaccine (eg, myocarditis), and if so, what?

Countries that have begun mass vaccination of vaccine boosters have so far seen no cases of rare or very rare adverse effects from boosters.

By aamritri

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