TORONTO — A large-scale study in the U.K. investigating breakthrough infections has found that out of 1.2 million people who received a first dose of the COVID-19 vaccine, only 0.5 per cent subsequently tested positive for the virus, encouraging evidence of the vaccine’s effectiveness.
The study also found that those who had one or two doses had significantly lower odds of severe disease or hospitalization than unvaccinated people if they contracted the virus — and a lower chance of experiencing long COVID symptoms.
“We saw these really quite remarkable, statistically significant changes in both risk of infection, and also what infection felt like for those individuals,” Dr. Claire Steves, the study’s lead scientist, told CTV News.
The study, which was published Wednesday in The Lancet Infectious Disease Journal, tracked 1.2 million people in the U.K. who had been vaccinated with Pfizer, Moderna or AstraZeneca in the first half of this year, as both the Alpha and Delta variants were circulating.
Researchers found that the risk of infection was dramatically reduced — for every 1,000 people who got one dose of Pfizer, Moderna or Astra Zeneca, only five people developed breakthrough infections.
For every 1,000 who got two doses, just two people contracted COVID-19 after. That’s only 0.2 per cent.
More than 971,000 people who participated in the study had received both shots of the vaccine.
Steves pointed out that these figures took into account the exposure of an individual, and added that the risk might be slightly higher in certain situations where the exposure risk is higher.
“But what we think doesn’t really get affected by that is the characteristics of what does a breakthrough infection look like, and we saw that, overall, […] each individual symptom was much less frequent in people who got a breakthrough infection,” she said.
The double vaccinated were 73 per cent less likely to end up in hospital.
Most breakthrough cases were asymptomatic, or had few symptoms.
“We found that people who got breakthrough infections were about twice as likely actually to have no symptoms at all,” Steves said.
She explained that this was important for two reasons: it showed that the risk of even mild disease was reduced in those who are vaccinated, but it also showed that we shouldn’t rely on symptoms alone to identify breakthrough cases moving forward.
Those who are in contact with vulnerable individuals on a regular basis — healthcare workers, caretakers, those who are visiting elderly relatives frequently — should be taking rapid tests to ensure they don’t have an asymptomatic case when visiting those who are more at risk if they contract COVID-19, Steves said.
Christopher Richardson, a professor at Dalhousie University, told CTV News that the results of the U.K. study are “uplifting” to hear.
“Vaccination is really important. And it works,” Richardson said. “The results are just so astounding, and they show you you’re going to survive if you’ve gotten the vaccine.
“I think all this isolation […] during the COVID era has made people a little bit depressed, and they’re frustrated, I see it, they’re impatient and they want it all over. They want everything to become normal again. And I think that there’s hope on the horizon.”
The study is also the first to show that double vaccinations cut the risk of developing long COVID symptoms by half, in the cases where a vaccinated person did get infected.
“That’s something that’s really important for many people, especially young people who are maybe less at risk of acute disease,” Steves said. “It gives people a real positive personal incentive to get a vaccination.”
For Lorraine Graves, who developed long COVID in 2020 and has suffered with extreme fatigue in the year since, it’s “really hopeful” to hear that vaccination could prevent more suffering like hers.
“When you think of COVID, don’t think of a really bad flu,” she said, going on to describe her disabling experience of long COVID.
“It’s not just being a little tired and not quite getting over it, it’s losing your productive life. Vibrant people are now bedridden. I’m so much better than I was last summer, but it’s been a year and a half, and now I can be up for three hours. If I have a whole bunch of coffee, and have rested a lot the day before, I can talk to you like this, but there are times, probably after this, where I’m not going to be able to put sentences together, I will be so tired, just from the excitement of this.
“Instead of participating in life, you watch it go by.”
If getting vaccinated can give you a better chance of not contracting COVID-19, or a better chance of avoiding long COVID if you do contract the virus, “why would you not get a vaccine?” she said.
“When it’s available to adolescents and teens, that means your child’s brain is not going to be disabled,” Graves added. “That means your child is not going to be spending a year or two on the couch, unable to go to the school or participate in anything. That means your child isn’t going to be disabled by pain that nothing treats.”
Richardson added that complications from the COVID-19 vaccines are very rare.
“They’re safer than the more classical vaccines like measles and polio, because they don’t use even live viruses,” he said.
Although the risk of breakthrough infections was rare across the board in the study, researchers noted that there were a few groups at a higher risk of developing more serious breakthrough infections.
Those considered medically obese and those over 60 who were frail or had other health conditions were at a higher risk. Researchers also found that people who lived in economically poor areas were at a greater risk, something they theorized could be down to lower vaccination cover, greater transmission rates and more dense populations.
“And so when you’re interacting with somebody [who falls into one of these groups], then you need to make sure that you take precautions as much as possible, even if you’ve been double vaccinated, and even if you’re asymptomatic,” Steves advised.
Health-care workers themselves are also still more at risk even when double vaccinated. A research letter published in The New England Journal of Medicine on Wednesday tracked an outbreak of COVID-19 cases among fully vaccinated health-care workers in July at the University of California San Diego Health.
In June, there were five cases of COVID-19 among fully vaccinated workers. In July, there were 94 cases. This rise in breakthrough COVID-19 cases coincided with the end of California’s mask mandate and the rise of the Delta variant in the state.
The letter stated that these results show that even though vaccines have been shown to be quite effective, that doesn’t mean that we should get overconfident and drop all safety measures.
“Our findings underline the importance of rapidly reinstating nonpharmaceutical interventions, such as indoor masking and intensive testing strategies, in addition to continued efforts to increase vaccinations,” the letter stated.
In the U.K. study, those with kidney disease also were more prone to breakthrough infections, but researchers were unsure whether this was due to being exposed more because of regular trips to healthcare facilities for dialysis treatment, or simply that these patients are immunocompromised.
The U.K. study did rely on self-reported symptoms, and some of the data regarding symptoms may be imperfect because of this, researchers acknowledged. It also started in December 2020, and ended in early July, and at the beginning of this period, the Delta variant was less widespread.
However, Steves pointed out that by June in the U.K., Delta was the most prevalent strain of COVID-19 already.
“Because our study looks at a time when Delta variant is the most prominent, we can see that actually, our findings are robust to Delta,” she said.
The public health message, researchers say, is that this fall, social distancing, masks and frequent testing or rapid tests, will still be needed.
Steves added that “urgent research” on booster shots is still needed for those groups who are still at a high risk, such as elderly people and the immunocompromised.
But for now, this huge study provides a much-needed boost of positive news for everyone.
“I think it gives us some hope,” Richardson said.
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