Many people are worried about reports of “breakthrough” COVID-19 infections overseas, from places like Israel and the United States, reports The conversation.
The breakthrough infection
A breakthrough infection is when someone tests positive for COVID after being fully vaccinated, regardless of symptoms.
The good news is most breakthrough infections usually result in mild symptoms or none at all, which shows us that vaccines are doing exactly what they’re supposed to do — protecting us from severe disease and death. Vaccines aren’t designed to protect us from getting infected at all.
People with breakthrough infections can go on to infect others. Preliminary evidence indicates immunised people can have high levels of virus in the nose, potentially as high as unvaccinated people.
Is the current vaccine effective against the other variants?
Two studies from the United Kingdom suggest the immunity we get from COVID vaccines wanes over time, after about four to six months.
While the more-infectious Delta variant continues to circulate, waning immunity will lead to more breakthrough infections.
Waning immunity means booster doses will likely be needed to top up protection, at least for the next couple of years while the virus continues to circulate at such high levels.
But the reduction isn’t large currently. Vaccine effectiveness is very high to begin with, so incremental reductions due to waning won’t have a significant effect on protection for some time.
Given most people in Israel are vaccinated, many COVID cases in hospitals are vaccinated. However, the majority (87%) of hospitalised cases are 60 or older. This highlights what’s known about adaptive immunity and vaccine protection — it declines with age.
Our currently approved vaccines were modelled on the original strain of the virus isolated in Wuhan, not the Delta variant, which is currently dominant across most of the world. This imperfect match between vaccine and virus means the level of protection against Delta is just a little lower.
Because the level of effectiveness is so high to begin with, this small reduction is negligible. But the effects of waning over time may lead to breakthrough infections appearing sooner.
mRNA vaccines in particular, like Pfizer’s and Moderna’s, can be efficiently updated to target prevalent variants, in this case Delta. So, a third immunisation based on Delta will “tweak”, as well as boost, existing immunity to an even higher starting point for longer-lasting protection.
Amount of exposure to the virus
If we’re fully vaccinated and have merely fleeting contact with a positive case, we likely won’t breathe in much virus and therefore are unlikely to develop symptomatic infection.
But if you’re in the same room as a positive case for a long period of time, you may breathe in a huge amount of virus. This makes it harder for your immune system to fight off.
This may be one reason we’re seeing some health-care workers get breakthrough infections, because they’re being exposed to high viral loads. They could be a priority for booster doses.
Might unvaccinated kids be playing a role?
It’s unclear if children are contributing to breakthrough infections.
Vaccines aren’t approved for young children yet, so we’re seeing increasing cases in kids relative to older people. Early studies, before the rise of Delta, indicated children didn’t significantly contribute to transmission.
More recent studies in populations with vaccinated adults, and where Delta is the dominant virus, have suggested children might contribute to transmission. This requires further investigation, but it’s possible that if you’re living with an unvaccinated child who contracts COVID, you’re likely to be exposed for many, many hours of the day, hence you’ll breathe in a large amount of virus.
The larger the viral dose, the more likely you’ll get a breakthrough infection.
Potentially slowing the number of breakthrough infections is one reason to vaccinate 12 to 15 year olds, and younger children in the future, if ongoing trials prove they’re safe and effective in this age group. Another is to protect kids themselves, and to get closer to herd immunity .
About “the extra protection”
Breakthrough infections likely confer extra protection for people who’ve been fully vaccinated — almost like a booster dose.
We don’t have solid real-world data on this yet, but it isn’t surprising as it’s how our immune system works. Infection will re-expose the immune system to the virus’ spike protein and boost antibodies against the spike.
Extra protection is just a silver lining if you do get a breakthrough infection.
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Source: The conversation
