Why do people who are fully vaccinated test positive for Covid?


Phoenix Suns basketball star Chris Paul, British Health Minister Sajid Javid, and American Olympic gymnast Karaeke have one thing in common: they have all tested positive for the coronavirus despite being vaccinated.

No vaccine is 100% effective, so scientists have been anticipating “breakthrough infections.” In most cases, the symptoms are mild.

However, as the new surge in Covid-19 cases conflicts with the global vaccination campaign that provides more than 200 million injections per week, more and more people are asking: “How protected am I?”

How many fully vaccinated people test positive?

Experts said that although rumors of breakthrough infections may make such cases widespread, the actual number is still small and generally in line with expectations.

“There is no such thing as a perfect vaccine… The use of Covid is no exception,” said Professor William Schaffner, an infectious disease expert at Vanderbilt University.

For example, the yellow fever vaccine is widely regarded as the most effective live virus vaccine ever invented, and 98% of vaccinators can develop lasting immunity with just one injection. But even so, it means that an average of 2% of people will still be infected.

Most of the leading Phase 3 trials of the Covid-19 jab show that it is more than 90% effective against symptomatic infections. Real world research The effectiveness of the United Kingdom, Israel, and Canada indicates that the vaccine’s effectiveness outside the test environment is slightly lower, possibly due to the spread of the more vaccine-resistant Delta variant. Depending on the vaccine, it is estimated that the protection rate against symptomatic infection is between 60% and 90%.

According to data from the Department of Public Health of the United Kingdom, in the four weeks as of July 19, about 17% of the 105,598 cases of Delta variant reported across England were fully vaccinated people. PHE counts people as fully vaccinated 14 days after the second vaccination.

Anthony Masters, a member of the Royal Statistical Society of the United Kingdom, said that as the coverage of vaccines expands, fully vaccinated people may account for a “larger percentage” of cases, especially if they face higher exposure due to higher social integration Among the young at risk.

“If you have very high coverage at different ages, the cases may become [in] Accounted for the majority of the fully vaccinated population,” he said. About 55% of the British population has Received two doses Until July 21.

In Israel, nearly 60% of the population is vaccinated, and coverage is more evenly distributed across all age groups. In the week ending July 21, 52% of the approximately 6,000 people who tested positive were vaccinated.

Are some fully vaccinated people more likely to get sick than others?

A fully vaccinated person who tests positive for Covid-19 rarely becomes seriously ill. According to PHE’s real-world study, the BioNTech/Pfizer vaccine has an effective rate of 96% for hospitalization, while the Oxford/AstraZeneca vaccine has an effective rate of 92%.

But Natalie Dean, a professor of biostatistics at Emory University in Atlanta, emphasized that these numbers are averages, and the efficacy depends on people’s existing risk status. “In terms of vaccines and risks, everything is relative,” she said.

For example, the “Financial Times” analysis of global infection mortality shows that an 80-year-old with double spurs now faces roughly the same risk of death as an unvaccinated 50-year-old.

In England, the launch of the vaccine is staggered from the oldest to the youngest. 9 out of every 10 people over the age of 50 have been fully vaccinated, and in the four weeks ending July 19, they were admitted to the hospital for the Delta variant. 30% of the 1,788 people were fully vaccinated. Was vaccinated. Since February, of the country’s 460 deaths related to the Delta strain, about half are people who have also been fully vaccinated.

Masters said: “This is just a reflection of the elderly’s very high vaccination rate.” “This is an abnormal sign. [a] Successfully launched.If everyone [was] Fully vaccinated, by definition, everyone who goes to the hospital or dies will be fully vaccinated. ”

Masters said that about two-thirds of the people who died on British roads were wearing seat belts, but this was due to a nearly 99% usage rate. He added that the same logic applies to severe illness and death among highly vaccinated people.

Vanderbilt’s Schaffner added that if not vaccinated, those with unpleasant but mild symptoms may develop serious illness and even die. “Whenever my patients tell me that they are still suffering from a mild illness despite being vaccinated, I always say that I am glad you are still complaining here.”

The chart shows why the high percentage of double stingers during hospitalization does not mean that the vaccine has failed. When a very high percentage of people are fully vaccinated, although the vaccine works well, a large proportion of cases and hospitalized patients will be a double blow.When the proportion of fully vaccinated is low, the proportion of cases and hospitalizations for double spurs is smaller, but more people are hospitalized overall

Can you test your degree of protection?

not yet. The easiest way to understand how much immunity a vaccine produces in the human body is to measure the presence of neutralizing antibodies in the blood. But T cells and B cells that complement the human immune system also play a role, and scientists still don’t know which benchmarks best understand the effectiveness of vaccines.

Danny Altmann, professor of immunology at Imperial College London, explained that commercially available antibody tests only show whether a person has Covid-related antibodies, but it is best to understand immunity as “scale or continuum” . “This is not binary. You are unsafe or unsafe, protected or unprotected. People have varying degrees of protection for vaccines.”

This immunity range can be mapped by a test called a neutralization test, which analyzes how many times antibodies extracted from blood can be diluted in the laboratory and still neutralize the virus.

Altmann said that in extreme cases, people with weakened immune systems may only be able to produce enough antibodies to withstand a 100-fold dilution. In contrast, healthy young people may have enough 10,000-fold dilution and “may not be infected.”

If scientists can determine the midpoint between these two extremes, Altmann said: “Vaccine manufacturers will be able to update vaccines with new variants more quickly, and policymakers can better determine who needs booster doses the most.”

What does an imperfect vaccine mean for herd immunity?

Kit Yates, a mathematical biologist at the University of Bath, warned that vaccines provide imperfect protection against infection, which means that herd immunity may be “impossible” if the vaccination rate does not exceed 90%.

“The leaked vaccine may make herd immunity out of reach, especially in the face of [the] delta [variant],” He says.

The chart shows that if there is no vaccine, the daily number of hospitalizations for new coronary pneumonia in England will exceed the winter peak

Adam Kucharski, an epidemiologist at the London School of Hygiene and Tropical Medicine, said that since the UK is expected to have more than 100,000 cases per day by late August, the impact of imperfect vaccines “will soon be Become clear”.

PHE estimates that, on average, the Covid-19 vaccine used in the UK is 91% to 97% effective in preventing hospitalization.

Kucharski warned that small differences could have a major impact on the impact of this wave of infections on the British healthcare system. “If you reverse the numbers, you will know how ineffective the vaccine is. A 9% ineffectiveness instead of a 3% ineffectiveness means that the number of hospitalizations has tripled.”

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