T cells kick in once you’ve been infected. Their task is to protect you from falling seriously ill with a germ. Rather than chasing after the invader and catching it before it infects you, T cells kill cells in your body that have already been infected so the uninfected ones have a better chance of survival.
So if a germ, for instance SARS-CoV-2, the virus which causes Covid-19, has managed to sidestep your antibodies and penetrate your cells, T cells pick up the mess by sniffing out which cells have been hijacked and getting rid of them.
One specific T cell, a CD8, does the killing. That’s why they’re also known as killer T cells. By killing off infected cells, they prevent you from getting sicker.
You also have something called helper T cells, known as CD4s, which help B cells to make antibodies and CD8s to kill germs that invade your body.
How do scientists test if a virus can outsmart your antibodies?
Finding out if antibodies can fight off a variant means scientists must take the blood from someone who was vaccinated against Covid, previously infected with SARS-CoV-2, or both, and test how well the antibodies in the blood samples stop the variant in its tracks, explains Alex Sigal, a virologist at the Africa Health Research Institute.
To do this, blood samples are mixed with the variant and put in a small glass holder called a petri dish to see what happens. When researchers monitor what happens in the petri dish, they’re looking to see how well the antibodies derived from vaccines or natural infection can block the virus. That way, they can find out if a variant can sidestep antibodies, and if so, to what extent.
Such studies about Omicron have started to trickle in.
They compared those results with the blood of vaccinated people that got blended with the original form of SARS-CoV-2 that was dominant during our first Covid wave, so that they could work out if Pfizer’s vaccine provides the same amount of protection against both forms of the virus.
They also looked at how well Pfizer worked for people who had both been fully vaccinated and who also had antibodies from previous natural infection with a variant other than Omicron (e.g. Beta or Delta).
The scientists compared the three groups’ results with each other because when Covid vaccines were designed, they were developed to target the original form of the virus as there were no other variants at the time.
The comparison therefore allowed the researchers to see if vaccine-derived antibodies, as well as a combination of the antibodies people developed from infection and those that they produced as a result of vaccination, provided different levels of protection against Omicron and the original form of SARS-CoV-2 and Omicron.
Because antibodies protect us against getting infected, such lab tests, called antibody titers, can only tell us how a variant influences our protection against contracting a virus — it can’t tell us how well we’re protected against falling seriously ill with a variant.
The results?
A 41-fold drop in how well antibodies from Pfizer’s Covid jab prevent infection and stop the Omicron variant from invading cells (compared to how well they could do this against the form of the virus that dominated South Africa’s first wave).
This roughly translates to vaccine efficacy (against infection) of 22.5%, which the study authors caution compromises “the ability of the vaccine to protect against infection”.
However, people who had been fully vaccinated and also previously infected, enjoyed higher levels of protection.
Why it’s important to get vaccinated — even if you’ve had Covid before
The good news, Sigal, the lead researcher, says, is that Omicron couldn’t completely escape our antibodies. The more antibodies we have, the better our chances are of protection against infection. That is why previous infection, combined with vaccination, increases protection (because it results in more antibodies to deflect the virus).
On the up side, although there’s no way to know exactly how many people in South Africa have been infected with SARS-CoV-2, studies have shown that the number of actual Covid cases is likely considerably higher than those reported, so a large proportion of people living in South Africa could have natural immunity.
The National Institute for Communicable Diseases (NICD), for instance, estimates that less than 10% of Covid cases are reported, meaning roughly 45% of the country’s population has been infected with SARS-CoV-2 and would have developed antibodies as a result of it, which can provide the added protection that South African researchers showed helped reduce someone’s chances of getting infected with Omicron.
In South Africa, researchers found that the relative risk of someone who has had Covid, and then got exposed to the SARS-CoV-2 virus again, was close to three times higher to get reinfected if they were exposed to the Omicron variant compared to exposure to the Delta or Beta variants.
A day after the South Africans published their results, Pfizer released their own results of a similar study via a press release. They also found a decrease in protection against Omicron infection, although slightly lower — 25-fold — than Sigal and his colleagues, but Pfizer’s scientists had a similar conclusion: Two doses of Pfizer “may not be sufficient to protect against infection with the Omicron variant”.
This is backed up by real-world data that was released on 14 December by South Africa’s largest medical scheme administrator, Discovery Health. The data, based on the first three weeks of South Africa’s Omicron wave, showed that the protection that two jabs of Pfizer provided against getting infected with the Delta variant in South Africa dropped from 80% to 33% with Omicron.
Pfizer’s research found that receiving a third shot of the vaccine increased protection against infection 25-fold (when compared to two doses). In other words, an extra dose restored the reduced protection of two shots.
With regard to Johnson & Johnson (J&J), the other vaccine that South Africa uses, unpublished data shared by Penny Moore, a virologist at the University of the Witwatersrand, found that in a lab setting, the antibodies generated by the single dose jab dropped to undetectable levels against Omicron.
How do scientists know if a variant reduces our T cell protection?
Just because vaccines provide low levels of protection against infection with Omicron, doesn’t mean they don’t help to prevent us from falling seriously ill (their main purpose).
The tests scientists need to do to find out if a vaccine can protect us from severe disease — so if a variant influences how well our T cells can kill already infected cells — are considerably trickier, and also more time-consuming than antibody tests.
T-cell tests, or assays, as scientists call them, involve extracting white blood cells, freezing them (while keeping them alive), exposing the cells to artificially-made pieces of the spike protein of SARS-CoV-2, adding several different chemicals, or reagents, to run different tests and then assembling all the data and analysing it.
In short: T-cell assays involve far more than mixing a variant with antibodies contained in blood samples in a petri dish.
That’s why, up until now, we’ve mostly only seen antibody test results be released for Omicron.
But early data presented to the World Health Organisation, which will soon be published as a preprint, shows that T cell responses from the Pfizer vaccine are holding strong against Omicron. Tests are still being done assessing this aspect of J&J’s jab.
In addition, there are T-cell results for previous variants.
A November paper in Cell Host and Microbe showed that a single dose of J&J was able to trigger a strong T-cell response against both the Beta and Delta variants. This is why, despite these variants having the ability to outsmart antibodies to some extent, the vaccine was still able to offer high levels of protection against severe disease.
What we do have for Omicron, so far, is Discovery Health’s real-world data and also hospitalisation figures from the health department and NICD.
Discovery’s data found that although the protection that two shots of Pfizer’s jab provides against hospitalisation with Covid had dropped from 93% with the Delta variant to 70% with Omicron, this is still considerable protection (the WHO considers a Covid vaccine effective when it provides 50% protection).
Health department data shows that 19% of new COVID cases in the Delta wave were admitted to hospital in the second and third weeks of the Delta wave, while only 1.7% of cases have been admitted during the same period of the Omicron wave.
What does Omicron mean for the country’s hospitals?
NICD data shows an increasing decoupling between new cases and hospitalisations, so while new Covid cases during the Omicron wave are increasing at a much steeper rate than during the Delta wave, hospital admissions are rising at a considerably slower pace.
Figures also reveal that patients in our current wave stay in hospital for shorter periods than during the Delta wave, and, when they are hospitalised, a smaller proportion require oxygen or end up in high-care or intensive care units. Moreover, almost everyone who is admitted to health facilities with Omicron is unvaccinated.
Scientists don’t yet know if the lower hospitalisation rates are because Omicron causes less severe disease, whether vaccination of particularly older people, who are more vulnerable to falling seriously ill with Covid than younger people, are protecting them, or if it’s a combination of both factors.
The NICD, however, reports that in Gauteng, where South Africa’s Omicron outbreak started, that trend is starting to change, particularly with regards to children between the ages of 0-5, with the proportion of admissions of people of 60 years and older now increasing at a faster rate. The picture in provinces where Omicron outbreaks started after Gatueng, is, however, not yet clear and could still be different.
But it’s way too soon to tell if this trend will continue as the wave progresses.
“It’s too early to be making claims that Omicron causes mild disease — and in fact that’s quite a dangerous message to put out there,” says Richard Lessells, an infectious disease expert and scientist who was one of the scientists who identified Omicron in South Africa.
Covid jabs were designed first to prevent symptomatic disease and not to give you complete protection against getting infected. But preventing illness has become more difficult to achieve as new variants have emerged. So now, the focus has shifted to reducing how serious the illness is after you have been infected, rather than preventing it entirely.
The pro of T cells is that they step in when your antibodies need some extra support. So even if your first line of defence doesn’t succeed in fully protecting you, these killer cells come in and fire directly at the already infected cells, helping you keep the illness at bay. Also, part of the body’s immunity has antibodies helping T-cells to kill infected cells.
Although we don’t yet have clear data on the extent to which Omicron is able to reduce how efficiently T cells can kill off infected cells, scientists think it’s unlikely that the variant would have much of an effect.
One of the reasons researchers believe this is because killer T cells don’t just target one part of the spike protein of the SARS-CoV-2 virus (like antibodies do), so they’re less affected by mutations.
“T cells target the whole [spike] protein,” explains Wendy Burgers, a professor of medical virology at the University of Cape Town. “They’re less discriminatory, they go for anything. So because killer cells strike at hundreds of sites along the spike [where the virus attaches to human cells] as opposed to the more narrow approach of antibodies, they are far less likely to be rendered useless by changes to protein’s structure.”
Pfizer’s study found that “as 80% of epitopes in the spike protein recognised by CD8+ T cells are not affected by the mutations in the Omicron variant, two doses may still induce protection against severe disease”.
The advantage of this part of the immune response, according to Burgers, is that each person’s genetics influences the T cells attack formation.
“When it comes to T cells, unlike with antibodies, it is unlikely that there will be a population effect,” she says.
This means, according to Burgers, that even if the T-cell response does take a knock in some people, it’s not going to affect everyone in the same way (as happens with antibodies). So while antibody evasion means that some protection is lost in everyone, outmanoeuvring killer cells will only happen in some people.
Burgers explains: “It’s likely that a proportion of people may be affected and lose some of their immune response from these mutations — but what is left may be enough of a T-cell response to still protect [the population at large] from severe disease and death.”
So how protected from Omicron are you?
Early lab data shows Pfizer vaccination doesn’t provide much protection against infection, but that a third booster shot could potentially increase protection against infection.
But we don’t yet know for how long the protection that a booster shot might provide against getting infected with SARS-CoV-2, would last, as vaccine-derived immunity has been shown to wane over time.
But booster shots’ protection against falling seriously ill with Covid, would be less affected by waning immunity, because B cells, which produce antibodies, also come in the form of memory cells, whose job it is to produce additional antibodies when they come across a familiar foe. And where the number of antibodies people produce may decrease from about six months after vaccination, memory cells usually stick around for longer.
We also have real-world data, in the form of Discovery Health’s study and also the hospital and infection data that the NICD collects, that show that two Prizer jabs likely provide considerable protection against falling seriously ill with Omicron infection.
But since South Africa is only three to four weeks into its Omicron wave, and there is, so far, also little data available from other countries, it’s simply too early to tell, for sure, what impact Omicron will have on severe disease.
Lessells concludes: “Because to actually answer the question [of disease severity and vaccine protection] requires more time, more data, and very careful data analysis to really understand what we’re seeing.”
TORONTO – Health Canada has authorized Moderna’s updated COVID-19 vaccine that protects against currently circulating variants of the virus.
The mRNA vaccine, called Spikevax, has been reformulated to target the KP.2 subvariant of Omicron.
It will replace the previous version of the vaccine that was released a year ago, which targeted the XBB.1.5 subvariant of Omicron.
Health Canada recently asked provinces and territories to get rid of their older COVID-19 vaccines to ensure the most current vaccine will be used during this fall’s respiratory virus season.
Health Canada is also reviewing two other updated COVID-19 vaccines but has not yet authorized them.
They are Pfizer’s Comirnaty, which is also an mRNA vaccine, as well as Novavax’s protein-based vaccine.
This report by The Canadian Press was first published Sept. 17, 2024.
Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.
TORONTO – Sanniah Jabeen holds a sonogram of the unborn baby she lost after contracting listeria last December. Beneath, it says “love at first sight.”
Jabeen says she believes she and her baby were poisoned by a listeria outbreak linked to some plant-based milks and wants answers. An investigation continues into the recall declared July 8 of several Silk and Great Value plant-based beverages.
“I don’t even have the words. I’m still processing that,” Jabeen says of her loss. She was 18 weeks pregnant when she went into preterm labour.
The first infection linked to the recall was traced back to August 2023. One year later on Aug. 12, 2024, the Public Health Agency of Canada said three people had died and 20 were infected.
The number of cases is likely much higher, says Lawrence Goodridge, Canada Research Chair in foodborne pathogen dynamics at the University of Guelph: “For every person known, generally speaking, there’s typically 20 to 25 or maybe 30 people that are unknown.”
The case count has remained unchanged over the last month, but the Public Health Agency of Canada says it won’t declare the outbreak over until early October because of listeria’s 70-day incubation period and the reporting delays that accompany it.
Danone Canada’s head of communications said in an email Wednesday that the company is still investigating the “root cause” of the outbreak, which has been linked to a production line at a Pickering, Ont., packaging facility.
Pregnant people, adults over 60, and those with weakened immune systems are most at risk of becoming sick with severe listeriosis. If the infection spreads to an unborn baby, Health Canada says it can cause miscarriage, stillbirth, premature birth or life-threatening illness in a newborn.
The Canadian Press spoke to 10 people, from the parents of a toddler to an 89-year-old senior, who say they became sick with listeria after drinking from cartons of plant-based milk stamped with the recalled product code. Here’s a look at some of their experiences.
Sanniah Jabeen, 32, Toronto
Jabeen says she regularly drank Silk oat and almond milk in smoothies while pregnant, and began vomiting seven times a day and shivering at night in December 2023. She had “the worst headache of (her) life” when she went to the emergency room on Dec. 15.
“I just wasn’t functioning like a normal human being,” Jabeen says.
Told she was dehydrated, Jabeen was given fluids and a blood test and sent home. Four days later, she returned to hospital.
“They told me that since you’re 18 weeks, there’s nothing you can do to save your baby,” says Jabeen, who moved to Toronto from Pakistan five years ago.
Jabeen later learned she had listeriosis and an autopsy revealed her baby was infected, too.
“It broke my heart to read that report because I was just imagining my baby drinking poisoned amniotic fluid inside of me. The womb is a place where your baby is supposed to be the safest,” Jabeen said.
Jabeen’s case is likely not included in PHAC’s count. Jabeen says she was called by Health Canada and asked what dairy and fresh produce she ate – foods more commonly associated with listeria – but not asked about plant-based beverages.
She’s pregnant again, and is due in several months. At first, she was scared to eat, not knowing what caused the infection during her last pregnancy.
“Ever since I learned about the almond, oat milk situation, I’ve been feeling a bit better knowing that it wasn’t something that I did. It was something else that caused it. It wasn’t my fault,” Jabeen said.
She’s since joined a proposed class action lawsuit launched by LPC Avocates against the manufacturers and sellers of Silk and Great Value plant-based beverages. The lawsuit has not yet been certified by a judge.
Natalie Grant and her seven year-old daughter, Bowmanville, Ont.
Natalie Grant says she was in a hospital waiting room when she saw a television news report about the recall. She wondered if the dark chocolate almond milk her daughter drank daily was contaminated.
She had brought the girl to hospital because she was vomiting every half hour, constantly on the toilet with diarrhea, and had severe pain in her abdomen.
“I’m definitely thinking that this is a pretty solid chance that she’s got listeria at this point because I knew she had all the symptoms,” Grant says of seeing the news report.
Once her daughter could hold fluids, they went home and Grant cross-checked the recalled product code – 7825 – with the one on her carton. They matched.
“I called the emerg and I said I’m pretty confident she’s been exposed,” Grant said. She was told to return to the hospital if her daughter’s symptoms worsened. An hour and a half later, her fever spiked, the vomiting returned, her face flushed and her energy plummeted.
Grant says they were sent to a hospital in Ajax, Ont. and stayed two weeks while her daughter received antibiotics four times a day until she was discharged July 23.
“Knowing that my little one was just so affected and how it affected us as a family alone, there’s a bitterness left behind,” Grant said. She’s also joined the proposed class action.
Thelma Feldman, 89, Toronto
Thelma Feldman says she regularly taught yoga to friends in her condo building before getting sickened by listeria on July 2. Now, she has a walker and her body aches. She has headaches and digestive problems.
“I’m kind of depressed,” she says.
“It’s caused me a lot of physical and emotional pain.”
Much of the early days of her illness are a blur. She knows she boarded an ambulance with profuse diarrhea on July 2 and spent five days at North York General Hospital. Afterwards, she remembers Health Canada officials entering her apartment and removing Silk almond milk from her fridge, and volunteers from a community organization giving her sponge baths.
“At my age, 89, I’m not a kid anymore and healing takes longer,” Feldman says.
“I don’t even feel like being with people. I just sit at home.”
Jasmine Jiles and three-year-old Max, Kahnawake Mohawk Territory, Que.
Jasmine Jiles says her three-year-old son Max came down with flu-like symptoms and cradled his ears in what she interpreted as a sign of pain, like the one pounding in her own head, around early July.
When Jiles heard about the recall soon after, she called Danone Canada, the plant-based milk manufacturer, to find out if their Silk coconut milk was in the contaminated batch. It was, she says.
“My son is very small, he’s very young, so I asked what we do in terms of overall monitoring and she said someone from the company would get in touch within 24 to 48 hours,” Jiles says from a First Nations reserve near Montreal.
“I never got a call back. I never got an email”
At home, her son’s fever broke after three days, but gas pains stuck with him, she says. It took a couple weeks for him to get back to normal.
“In hindsight, I should have taken him (to the hospital) but we just tried to see if we could nurse him at home because wait times are pretty extreme,” Jiles says, “and I don’t have child care at the moment.”
Joseph Desmond, 50, Sydney, N.S.
Joseph Desmond says he suffered a seizure and fell off his sofa on July 9. He went to the emergency room, where they ran an electroencephalogram (EEG) test, and then returned home. Within hours, he had a second seizure and went back to hospital.
His third seizure happened the next morning while walking to the nurse’s station.
In severe cases of listeriosis, bacteria can spread to the central nervous system and cause seizures, according to Health Canada.
“The last two months have really been a nightmare,” says Desmond, who has joined the proposed lawsuit.
When he returned home from the hospital, his daughter took a carton of Silk dark chocolate almond milk out of the fridge and asked if he had heard about the recall. By that point, Desmond says he was on his second two-litre carton after finishing the first in June.
“It was pretty scary. Terrifying. I honestly thought I was going to die.”
Cheryl McCombe, 63, Haliburton, Ont.
The morning after suffering a second episode of vomiting, feverish sweats and diarrhea in the middle of the night in early July, Cheryl McCombe scrolled through the news on her phone and came across the recall.
A few years earlier, McCombe says she started drinking plant-based milks because it seemed like a healthier choice to splash in her morning coffee. On June 30, she bought two cartons of Silk cashew almond milk.
“It was on the (recall) list. I thought, ‘Oh my God, I got listeria,’” McCombe says. She called her doctor’s office and visited an urgent care clinic hoping to get tested and confirm her suspicion, but she says, “I was basically shut down at the door.”
Public Health Ontario does not recommend listeria testing for infected individuals with mild symptoms unless they are at risk of developing severe illness, such as people who are immunocompromised, elderly, pregnant or newborn.
“No wonder they couldn’t connect the dots,” she adds, referencing that it took close to a year for public health officials to find the source of the outbreak.
“I am a woman in my 60s and sometimes these signs are of, you know, when you’re vomiting and things like that, it can be a sign in women of a bigger issue,” McCombe says. She was seeking confirmation that wasn’t the case.
Disappointed, with her stomach still feeling off, she says she decided to boost her gut health with probiotics. After a couple weeks she started to feel like herself.
But since then, McCombe says, “I’m back on Kawartha Dairy cream in my coffee.”
This report by The Canadian Press was first published Sept. 16, 2024.
Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.
VANCOUVER – Mayors and other leaders from several British Columbia communities say the provincial and federal governments need to take “immediate action” to tackle mental health and public safety issues that have reached crisis levels.
Vancouver Mayor Ken Sim says it’s become “abundantly clear” that mental health and addiction issues and public safety have caused crises that are “gripping” Vancouver, and he and other politicians, First Nations leaders and law enforcement officials are pleading for federal and provincial help.
In a letter to Prime Minister Justin Trudeau and Premier David Eby, mayors say there are “three critical fronts” that require action including “mandatory care” for people with severe mental health and addiction issues.
The letter says senior governments also need to bring in “meaningful bail reform” for repeat offenders, and the federal government must improve policing at Metro Vancouver ports to stop illicit drugs from coming in and stolen vehicles from being exported.
Sim says the “current system” has failed British Columbians, and the number of people dealing with severe mental health and addiction issues due to lack of proper care has “reached a critical point.”
Vancouver Police Chief Adam Palmer says repeat violent offenders are too often released on bail due to a “revolving door of justice,” and a new approach is needed to deal with mentally ill people who “pose a serious and immediate danger to themselves and others.”
This report by The Canadian Press was first published Sept. 16, 2024
