The delta mutant is twice as contagious as the original strain of coronavirus that causes COVID-19 disease and is due to its ability to infect a large number of people, including a few wholly vaccinated. It will be even more difficult to achieve. Herd immunity.
Dr. Ricardo Franco, an associate professor of infectious diseases at the University of Alabama at Birmingham, spoke at a briefing at the Infectious Diseases Society of America on Tuesday about the definition of herds. Immunity.
Being infected with Delta means that both vaccinated and unvaccinated people carry high viral load compared to other viral strains. Experts say that if the virus is easy to spread, it means that the threshold for herd immunity is even higher than before.
To achieve herd immunity, up to 85% or even 90% of the population may need immunity to the virus. 50%, 60% also 70% to 85% For early strains of SARS-CoV-2 virus. “In the case of Delta, the threshold estimate is well above 80% and probably close to 90%,” Franco said.
“The more infectious, the higher the number,” Dr. Gabor Keren, chair of the Johns Hopkins University School of Emergency Medicine, said in an interview last week. (He predicts that the new threshold will be at least 85%.)
Experts say higher thresholds may mean that we need higher immunity rates, which will create challenges for countries struggling to be shot with weapons.Vaccination It’s ticking These days, they have been almost flat for a few weeks, 58.2% Of the US qualified personnel, those over the age of 12 are fully vaccinated as of Wednesday.
“The higher the threshold, the better our vaccination campaign needs to be,” Franco said in an interview.
The mechanism of herd immunity is as follows.
Herd immunity is an epidemiological concept, not “mathematical certainty”. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and chief medical adviser to President Joe Biden, said. In June.. Assess how many people need to be immune to the disease in order to establish a baseline of protection for the entire community. For example, to prevent outbreaks, at least 95% of the population must be vaccinated against measles.
Herd immunity, which takes into account the combination of vaccine protection and innate immunity from infection, is calculated based on the rate of infection. It uses a basic reproduction number, often referred to as R0.
According to Franco, the original strain of the virus has a R0 of 2.5, and the first alpha mutant identified in the UK has a R0 of between 4 and 5. R0 of the delta is believed to be between 5 and 8.
“this is [strain] Jennifer Kates, Head of Global Health and HIV Policy at the Kaiser Family Foundation, said:
This means that in the absence of other mitigation measures such as masks and vaccinations, one person infected with Delta can infect the other 5-8 people with the virus.
In addition, new studies show that some fully vaccinated people can become infected with Delta. NS study Published on friday 74% of people Those who were positive for COVID-19 in a recent outbreak in Massachusetts were completely vaccinated.
Brian Abrahams, an analyst at RBC Capital Markets, told MarketWatch this week: “Therefore, the previous idea that 60% or 65% of the population is exposed to or vaccinated against the virus would be a threshold. Perhaps it is no longer exactly true. “
However, there are other factors to consider. We do not know how many people have been infected with the virus. When the pandemic first occurred, it took months to start and run the test. Not everyone is tested.about 40% The proportion of people infected with the virus is considered asymptomatic. They can only be tested as part of workforce or school surveillance, or if exposed to people who test positive. The results of the convenient home COVID-19 test are not tracked.
“We may be close to that [threshold] The number of cases is higher than actually expected, “Abraham added.
Here’s why healthcare professionals are worried about Delta:
The immediate concern for healthcare professionals is the number of people who are ill, hospitalized, and dying.
The average number of new cases each day this week will track the number of people who tested positive in late October. At that time, there was no COVID-19 vaccine approved for use in the United States.
The average of 7 days to move is 84,389 cases per day and 354 deaths per dayAs of August 2, according to the CDC.When it comes to that hospitalizationAs of August 1, the 7-day moving average is 40,453 per day.
However, public health experts are also concerned that circulating the virus to infect more people will increase the number of mutations that can evolve into a more efficient and dangerous form of SARS-CoV-2. doing. (Not all mutations turn into mutants, and not all mutants are more harmful.)
“We can only expect people to be vaccinated to put more pressure on them. [on the virus] It reduces the chances of variants continuing to emerge, “says Franco. “The more virus circulation, the more likely it is that there will be more variants with that capability. The less virus circulation, the less likely it is.”
(Dr. Eric Topol, director of the Scripps Research Translational Institute, said when asked if the virus could mutate in a small number of vaccinated people with breakthrough infections, “the person is immune. It is unlikely to be any material method unless it is inadequate. “)
The current surge is not expected to peak until some time in September. According to experts, data from delta-led surges in India and the United Kingdom show that new cases can suddenly decline when the delta peaks.
Kates of the Kaiser Family Foundation said there is a theory that the duration of Delta infection may be shorter than the duration of infection with the original virus.
For now, much of the focus of public health has been to encourage or mandate unvaccinated people to fire. Reintroduction of mitigation measures It’s like wearing a mask or keeping a social distance to protect both unvaccinated and vaccinated from the delta.
“Vaccination is really the ticket for the future,” Kates said. “Vaccines work like almost every vaccine we have. In fact, I think people forget that many vaccines work by preventing disease. Not necessarily real. It does not always prevent infection. “
As more infectious delta mutants circulate, public health experts say herd immunity has become a farther goal.
Source link As more infectious delta mutants circulate, public health experts say herd immunity has become a farther goal.