The COVID-19 delta variant which is already in more than 104 countries has raised concerns among health officials globally as they see more breakthrough infections, which occur in fully vaccinated people, even though they are mild.
People who are fully vaccinated against Covid-19 are protected against hospitalization and probably death caused by the virus. But coronavirus cases among the fully vaccinated (breakthrough Covid cases) are still being seen among those who have had two doses (2 jabs).
Experts note that, while it’s rare for vaccinated people in the U.S. or Europe to get sick from Covid, breakthrough cases are happening for a number of reasons.
For a start, none of the vaccines being deployed globally is 100% effective at preventing the infection.
In addition, new Covid strains such as the highly infectious delta variant, which is now prevalent around the world, have complicated the efficacy picture. There are also incomplete data into how long immunity from Covid lasts following vaccinations.
The alarm was raised over breakthrough Covid cases when preliminary data in Israel, which had one of the fastest vaccination programs in the world, published in July found that the Pfizer-BioNTech Covid-19 vaccine was just 39% effective, on average, at preventing symptomatic disease.
The efficacy figure, which is based on an unspecified number of people between June 20 and July 17, is down from an earlier estimate of 64% two weeks ago and conflicts with data out of the U.K. that found the shot was 88% effective against symptomatic disease caused by the variant.
Comparing the results is tricky, however, given differences in the nature of the vaccination programs in both countries (Israel gave all its adult population the Pfizer vaccine, for example, while in the U.K. there are several vaccines in use, with the Pfizer-BioNTech shot predominantly given to younger people) as well as differences in the study dates, age groups and Covid testing regimes involved, differences are likely to abound.
The analysis, which was carried out as the delta variant became the country’s dominant strain, still found that having two doses of the shot provided strong protection against severe illness and hospitalization.
However, Pfizer, in a statement, indicated that a third dose may be helpful after analysis from its phase three study showed a decline in efficacy against symptomatic infection after four to six months.
“Initial data of a third dose of the current vaccine demonstrates that a booster dose given at least 6 months after the second dose elicits high neutralization titers against the wild type and the Beta, which are 5 to 10 times higher than after two primary doses,” the company said.
The data appeared to show waning effectiveness of the Pfizer-BioNTech shot, however, the vaccine was only 16% effective against symptomatic infection for those individuals who had two doses of the shot back in January. But for people that had received two doses by April, the efficacy rate (against symptomatic infection) stood at 79%.
Isaac Bogoch, an infection disease professor at the University of Toronto stated that “We have to be mindful that, with time, the effectiveness of these vaccines may wane”.
He stressed that the shots are still highly effective in preventing severe infection, helping hospital systems not get too overwhelmed heading into the colder months. That being said, “we’re still in the Covid era and anything can happen,” he said.
“We have to be prepared and we have to envisage that people may need a booster at some point. This close surveillance that’s happening in countries like Israel, the U.K. and other parts of the world is going to be very helpful in driving policy if and when we do need boosters”, he added.
Similar to the Israeli data, the English data also concluded that after two doses the Pfizer-BioNTech Covid vaccine is highly effective against hospitalization from the delta variant (the English data found the vaccine to be 96% effective, the Israeli data found it to be 88% effective against hospitalization, on average). In addition, English data found that the Oxford-AstraZeneca vaccine was 92% effective in preventing hospitalization after two doses.
Initial vaccine efficacy data following clinical trials, released by Pfizer and BioNTech last year, showed that the vaccine was 95% effective against infections from strains of the virus that were circulating at the time.
“The delta variant is known to be highly infectious, and as a result, we can see from our data and others’ that breakthrough infections are happening in fully vaccinated people. We need to better understand how infectious fully vaccinated people who become infected are, as this will help to better predict the situation in the coming months, and our findings are contributing to a more comprehensive picture of this”, Isaac stated.
Professor Lawrence Young, a virologist at the University of Warwick’s Medical School in the U.K., stated that cases of Covid in fully vaccinated people are a reminder that “no vaccine is 100% effective.”
“There will always be a proportion of individuals who will still remain susceptible to infection and illness,” he added.
“There are also two other factors that impact vaccine effectiveness: (1) waning immunity — we still don’t know how long vaccine-induced protective immunity lasts. This is very likely to be a factor in those elderly and more vulnerable individuals who were vaccinated early in the vaccine rollout program,” he noted.
The second factor, he added, related to “breakthrough infections in vaccinated individuals due to the more infectious delta variant” which added weight to the case for booster vaccination programs, he said. As yet, the jury is still out on booster programs with a decision yet to be made.
The World Health Organization is warning that global Covid cases could pass 300 million by early next year if the pandemic continues in its current direction, calling on world leaders to slow the spread by providing more testing supplies, treatments and vaccines to poorer nations.
The projection came just a week after the WHO reported 200 million Covid cases worldwide and six months after the globe surpassed 100 million cases, WHO Director-General Tedros Adhanom Ghebreyesus said at a briefing Wednesday.
With four variants of concern on the WHO’s radar (including the surging, highly transmissible delta variant), Tedros said the total amount of unreported Covid cases makes the real tally “much higher” than what’s reported. “Whether we reach 300 million and how fast we get there depends on all of us,” Tedros added.
WHO officials expressed an urgent need on Tuesday for $7.7 billion in funding to help distribute vaccines, oxygen and medical care in low-income countries. Tedros echoed the push for supplies on Wednesday, requesting properly trained healthcare workers and increased treatment options for patients “at all ends of the clinical spectrum, from mild to severe disease.”
Last week, the WHO announced a moratorium on Covid vaccine booster shots, asking wealthy countries to stop using their extra doses so developing nations could start receiving a majority of the inoculations. Tedros previously issued a target to vaccinate 10% of the world’s population by the end of September and 40% by December.
The WHO has estimated that under 2% of Africa’s population is fully vaccinated, and some nations on the continent have yet to begin administering vaccinations. Comparatively, more than half of the U.S. population is fully vaccinated, according to the Centers for Disease Control and Prevention.
“We are all in this together, but the world is not acting like it”, Tedros concluded.