COVID: The Delta variant, Covid-19 symptoms and vaccine efficacy: What to know

As the Delta variant sweeps the globe, scientists are learning more about why new versions of the coronavirus spread faster, and what this could mean for vaccine efforts. The spike protein, which gives the virus its unmistakable shape, may hold the key.


Places with higher vaccination rates are keeping hospitalizations and deaths in check.


The Delta variant of the Covid-19 virus, the dominant strain in the U.S., is driving up cases in particular where vaccination rates are lower.


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Also known as B.1.617.2, the variant was first identified in India in late 2020.


Vaccines from Moderna Inc., Johnson & Johnson and Pfizer Inc. and partner BioNTech SE—the three shots authorized in the U.S.—were primarily tested in large clinical trials for their efficacy at preventing symptomatic disease, rather than their ability to prevent infection completely.


While the vaccines seem to be slightly less effective at preventing symptomatic Covid-19 from the Delta variant, research has shown that they remain highly effective at preventing serious illness and hospitalization.


Stalled for weeks, the portion of eligible Americans fully vaccinated against Covid-19 has ticked up recently to around 59%. Employer mandates and worries about the infectiousness and severity of the Delta variant are among the reasons people are getting vaccinated now, health officials say, particularly in states where Covid-19 cases have surged.


Here is what we know so far about the Delta variant and vaccines.


What is the Delta coronavirus variant?


The B.1.617 lineage, identified in October, refers to several variants of the virus that causes Covid-19.


The most concerning of the lineage is the Delta, or B.1.617.2, variant, which scientists say appears to have two advantages over earlier forms of the virus. It has been found to be more infectious and appears to be more effective at evading vaccines, though people who are fully vaccinated still have significant protection against illness.


What are the symptoms of the Delta variant?


In general, they are the same as the symptoms of other Covid-19 strains: fever, dry cough, shortness of breath, temporary loss of taste or smell, flulike respiratory and digestive problems, muscle aches and fatigue.


There is no data yet to show that the variant is causing atypical symptoms. There were reports in India suggesting that the virus was causing hearing loss, gangrene and other unusual symptoms, but scientists said an intense epidemic such as the one in India would tend to produce a spectrum of rare conditions, given the large number of infections.


How widespread is the variant in the U.S.?


More widespread every day. Delta now accounts for some 93% of known cases in the country, Centers for Disease Control and Prevention data shows.

Its spread is contributing to higher case counts, hospitalizations and deaths attributed to Covid-19. Almost everyone hospitalized with Covid-19 in recent weeks has been unvaccinated, doctors and public officials have said.


How contagious is this variant?


Scientists are still studying the virus, and their early conclusions aren’t definitive.


​The CDC said in a recent report that 127 vaccinated people infected with the Delta variant during a July outbreak on Cape Cod in Massachusetts appeared to have as high a viral load as 84 unvaccinated or partially vaccinated people who become infected.

British scientists estimate the Delta variant is from 40% to as much as 80% more infectious than the Alpha variant, or B.1.1.7, which was first identified in England last year, is now prevalent in the U.S. and is itself more contagious than the version of the virus that emerged in China in 2019.


Researchers in China reported in July that people infected with the Delta variant had about 1,000 times more viral particles in their respiratory tracts than those with the original strain.


The researchers also reported that people become infectious sooner.


Wendy Barclay, professor of Virology at Imperial College London, said swab tests suggest that Delta infects people with a greater virus load, which means they exhale more of it for others to catch. The mutations also appear to make the variant more effective at attaching itself to cells in human airways. The combination means that an infected person is—other things being equal—likely to infect more people and that people require less exposure to become infected.


Scientists don’t yet know whether the Delta variant is deadlier than other variants, but a study published in the Lancet medical journal estimated that the risk of hospitalization after infection with Delta could be 85% higher than with Alpha.


Is the Delta variant riskier for children than earlier variants?


Studies suggest that children are at significantly lower risk for serious illness or death from Covid-19. But some do fall sick, and several hundred children in the U.S. have died of the disease. Hospitals in some Southern and Midwestern states hit hard by Delta cases have reported treating younger Covid-19 patients than during previous surges, including more children.


The Delta variant threatens to infect more children because it is so contagious. The CDC changed its guidance for masks in schools in July, recommending that everyone in K-12 schools wear one this fall rather than just the unvaccinated, because of the Delta variant’s rapid spread.


Will existing vaccines work against this variant?


Designed to target the earliest coronavirus version, Covid-19 vaccines are holding up well against the Delta variant because it isn’t different enough from the earlier strain to evade the shots, researchers say. The vaccines generate neutralizing antibodies, which prevent the virus from entering cells and replicating. The number of antibodies generated in fully vaccinated people is still so high that enough antibodies can bind to the spike protein and block the virus, researchers say.


No vaccine is 100% effective. While vaccines in use in the U.S. and Europe appear to work well at preventing symptomatic Covid-19 and serious illness, research shows, they appear to work slightly less well than against earlier versions of the virus.


The CDC in August strengthened its recommendation that pregnant women be inoculated against Covid-19 along with most other people 12 years of age or older, saying data showed no increased risk of miscarriage or other safety concerns among those who were vaccinated during pregnancy.


Vaccines from Pfizer and BioNTech as well as from AstraZeneca PLC were highly effective against the Delta variant after two doses, according to a study of nearly 20,000 people published in July in the New England Journal of Medicine.


After two doses, the Pfizer vaccine was 88% effective at preventing symptomatic disease from Delta, compared with 36% efficacy after one dose, said the study, which was sponsored by Public Health England. The effectiveness at preventing symptomatic disease after two doses of AstraZeneca’s shot was 67%, compared with 30% after one dose.


A separate, preliminary study, however, found a much lower rate of efficacy against the variant for the Pfizer-BioNTech shots. Data released in late July by the government of Israel, which had one of the world’s fastest and most comprehensive vaccine rollouts, indicated that a two-dose course of the Pfizer-BioNTech vaccine is 41% effective in preventing symptomatic disease from the Delta variant.


The same Israeli study, based on a small sample size, found that the two-dose Pfizer vaccine is 88% effective at preventing hospitalization and 91% effective at preventing severe Covid-19 caused by the Delta variant.


Two doses of the mRNA vaccines are needed, researchers say, because neutralizing antibodies don’t work as well after just one dose and the body needs a higher level of antibodies given the presence of mutations. Also, the greater levels of neutralizing antibodies triggered by the two doses create a stronger immune response, virologists say.


A second dose boosts the numbers of T-cells, which hunt down infected cells and destroy them, and memory B-cells, which circulate in the blood and help churn out antibodies upon detecting a virus.


Moderna has said lab tests on blood samples taken from some vaccinated people showed promising signs that the company’s Covid-19 shot would protect against Delta and other variants. Johnson & Johnson has said that its shot showed promising signs in a small lab study of protecting against Covid-19.


Should I wear a mask even if I am vaccinated, to protect against Delta?


The CDC has said vaccinated people should wear a mask to prevent transmission of the virus in enclosed public places in parts of the U.S. that have substantial levels of new Covid-19 cases. The agency also said everyone in schools should wear masks this fall, regardless of vaccination status.


The agency said wider mask-wearing would help prevent vaccinated people with breakthrough infections from spreading the virus to the unvaccinated.


Asking vaccinated people to mask in high-risk areas is reasonable, said Ashish Jha, dean of the public-health school at Brown University, but he said that the decision to mask up or not might be different for people who are experiencing symptoms versus those who aren’t.


“If you’re vaccinated and you get infected and you have a fever and you’re hacking up a lung and you have a sore throat—no one would question that in that case, you need to wear a mask," Dr. Jha said. “The real question is, should asymptomatic vaccinated people be wearing mask to prevent spread to others? And I have not seen any data that supports that yet."


Some doctors say that because Delta can generate a heavier viral load than earlier variants, raising the risk of infection, masks can provide an added layer of protection on top of vaccination under conditions where Delta may be circulating, such as in close quarters with a group of people whose vaccination status is unknown.


“You need to be prudent even if vaccinated," said Dr. Diego Hijano, a pediatric infectious-disease specialist at St. Jude Children’s Research Hospital in Memphis, Tenn.


Can I get infected with this variant even after I have had Covid-19 or been vaccinated against it?


Yes, it is possible to become reinfected, though there is some evidence that second infections are tend to be less severe than the first. Virologists and infectious-disease specialists say that neutralizing antibodies, T-cells and memory B-cells generated by the vaccines are likely helping prevent severe disease. T-cells recognize viral cells in more ways than neutralizing antibodies and likely retain strength against variants, they said.


A Wall Street Journal analysis of data from health departments in 44 U.S. states and Washington, D.C., counted at least 193,204 breakthrough cases among vaccinated people between Jan. 1 and early August. That is 0.1% of the more than 136 million vaccinated people in those jurisdictions, showing that breakthroughs are uncommon.


Additionally, 28 health departments tracked breakthroughs since the start of July, when Delta emerged as the dominant strain of the virus. At least 11 states count more than half of breakthrough cases between July 1 and early August, while at least six others count more than a third during that period.


If I am vaccinated but become infected with the Delta variant, how likely am I to spread the virus?


Doctors and researchers say this is one of the most urgent questions about Delta.


Many researchers say vaccinated people who get a breakthrough infection, including via the Delta variant, are less likely to transmit Covid-19 to others. That is because, in most cases, breakthrough infections in vaccinated people will trigger strong immune responses that can quickly control and clear the infection. This, in turn, limits the amount of infectious virus being shed by the vaccinated.


“Vaccine or not, you’re infected," said Dr. Gabor Kelen, Director of the Department of Emergency Medicine at Johns Hopkins Medicine. “But the hope is that your viral load is significantly less than it would be if you weren’t vaccinated."


Factors affecting transmission include the viral load of the infected person but also the duration of exposure to another person and proximity of the two individuals, he said.


In a recent study of about 4,000 healthcare workers, people who became infected with Covid-19 after getting an mRNA-based vaccine carried less virus and had shorter cases than unvaccinated people who became infected. Researchers took samples from study participants before the Delta variant is believed to have arrived in the U.S.


However, researchers say that because Delta is so infectious, it might be more transmissible than previous linages and able to overcome the factor of lower viral shedding. The CDC said in a recent report that the high viral load in vaccinated people infected during the recent outbreak in Cape Cod demonstrated that they could spread the virus.


Among the 469 cases linked to that outbreak in the CDC report, nearly 75% were fully vaccinated. For people with breakthrough infections, almost 80% had symptoms of cough, headache, sore throat or fever. Four were hospitalized, and no deaths were reported, the CDC said. Infected people reported attending densely packed indoor and outdoor events at bars, restaurants and houses.


This story has been published from a wire agency feed without modifications to the text - Wall Street Journal