Why are fully vaccinated people test positive for Covid?


Phoenix Suns basketball star Chris Paul, UK Health Secretary Sajid Javid and US Olympic gymnast Kara Eaker have one thing in common: they have all tested positive for coronavirus despite the their complete vaccination.

No vaccine is 100% effective, so what scientists call “advanced infections” was always predicted. In most cases, the symptoms are mild.

However, as a new wave of Covid-19 cases has clashed with a global vaccination campaign giving more than 200m shots a week, more people are asking, “How am I protected?”

How many fully vaccinated people are testing positive?

While anecdotal accounts of revolutionary infections may make these cases feel widespread, the real numbers have remained small and were generally in line with expectations, experts said.

“There is no perfect vaccination. . . with Covid it’s no different, ”said Professor William Schaffner, an infectious disease specialist at Vanderbilt University.

Yellow fever jab, for example, is widely understood to be the most effective live virus vaccine ever invented, with a single dose generating long-term immunity in 98 percent of those vaccinated. But even this means that on average 2 percent of people still get infected.

Phase 3 trials for most major Covid-19 jabs showed an efficacy against symptomatic infections of more than 90 percent. Real world studies of efficacy in the UK, Israel and Canada suggest that vaccines show slightly lower efficacy outside the test environment, probably due to the spread of the more vaccine-resistant Delta variant. Estimates put protection against symptomatic infections, depending on the vaccine, between 60-90 percent.

According to Public Health England, about 17 per cent of the 105,598 Delta variants reported in England in the four weeks to 19 July were among people fully vaccinated. PHE counts people as completely vaccinated 14 days after their second dose.

Anthony Masters, a member of the Royal Statistical Society of the United Kingdom, said fully vaccinated people are likely to make up a “larger proportion” of cases where vaccine coverage has been extended, particularly in younger groups. who face a higher risk of exposure due to a larger social mix.

“If you have extremely high coverage for different ages, it’s plausible that homes can become so [in] among people who are fully vaccinated, “he said.” About 55 per cent of the UK population had he received both doses from July 21st.

In Israel, where nearly 60 percent of the population is fully vaccinated and coverage is more evenly distributed among age cohorts, 52 percent of about 6,000 people who tested positive in the week to July 21 were completely vaccinated.

Are some people completely vaccinated at higher risk of getting sick than others?

Very few fully vaccinated people who test positive for Covid-19 become seriously ill. According to real-world PHE studies, the BioNTech / Pfizer vaccine is still 96 percent effective against hospitalization, while the Oxford / AstraZeneca vaccine is 92 percent effective.

But Natalie Dean, a professor of biostatistics at Emory University in Atlanta, pointed out that these figures were average and that effectiveness depended on people’s existing risk profiles. “Everything is relative when it comes to vaccines and risk,” he said.

A Financial Times analysis of mortality rates from global infections, for example, suggests that an 80-year-old double-blind person now faces the same risk of mortality as an unvaccinated 50-year-old.

In England, where the spread of vaccines has been decimated from the oldest to the youngest and nine in 10 years over 50 years have been completely vaccinated, 30 per cent of the 1,788 people admitted to hospital for of the Delta variant in the four weeks to July 19 were completely vaccinated. About half of the 460 deaths in the country linked to the Delta strain since February were people who were also completely immunized.

“This is just a reflection of the uptake of vaccines which is very high among older people,” Masters said. “It’s perversely a marker of [a] successful rollout. Yes everyone [was] fully vaccinated, all those who went to the hospital or died will by definition be completely vaccinated ”.

About two-thirds of people who die on UK roads wear a seat belt, but this is a consequence of almost 99 per cent usage rates, Masters said. He added that the same logic is applied to serious diseases and deaths in highly vaccinated populations.

Vanderbilt’s Schaffner added that people who had unpleasant but mild symptoms would probably have suffered a serious illness, or even death, if they had not been vaccinated. “Every time my patients tell me they still have a mild illness despite the vaccination, I always say I’m glad you’re still here to complain.”

A graph showing why a high percentage of people double-stroke between hospitalizations does not mean that vaccines fail

Can you prove yourself as safe?

Not yet. The easiest way to understand how much immunity the vaccine has generated in a person is to measure the presence of neutralizing antibodies in the blood. But T cells and B cells, which complement the body’s immune system, also play a role and scientists remain unclear as to which benchmarks offer the best view of the vaccine’s effectiveness.

Commercially available antibody tests show only whether an individual has antibodies related to Covid or not, but immunity is best understood as a “scale or continuum,” explains Danny Altmann, professor of immunology at Imperial College. London. “It’s not binary. You are not safe or dangerous, protected or unprotected. People all have varying degrees of protection from the vaccine. ”

This range of immunity can be tracked with a test called neutralization analysis, which analyzes how many times the antibodies taken from the blood can be diluted in a laboratory and even neutralize the virus.

In the end, immunocompromised people can only generate enough antibodies to withstand a 100-fold dilution, Altmann said. In contrast, healthy young can get enough for a 10,000-fold dilution and are “probably impervious” to infection.

If scientists were able to establish the midpoint between the two extremes, Altmann said that “vaccine manufacturers will be able to update vaccines sooner for new variants and that policy makers can better determine which people need more doses. of reinforcement ”.

What do imperfect vaccines mean for band immunities?

Kit Yates, a mathematical biologist at the University of Bath, warned that the imperfect protection offered by the vaccine against infection meant that the band’s immunity could be “impossible” without taking vaccines above 90 percent. .

“Fugitive vaccines probably put the herd’s immunity out of reach, especially when they are found. [the] Delta [variant], ”He said.

Adam Kucharski, an epidemiologist at the London School of Hygiene and Tropical Medicine, said that with the UK anticipating more than 100,000 cases a day by the end of August, the implication of imperfect vaccines will “become apparent soon”.

PHE estimates that on average Covid-19 vaccines used in the UK are between 91 and 97 per cent effective in preventing hospitalization.

Kucharski warned that small differences could have a big effect on how widespread this wave of infections spreads to the British health system. “If you launch the number, you’re left with how ineffective the vaccines are and 9 percent ineffective rather than 3 percent ineffective means three times as many hospitalizations.”



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