Why vaccinated people can still get Covid-19

Natalia Sutherland
Source: 1News

This article was written before the Delta outbreak.

As the world continues to steadily roll out Covid-19 vaccines the number of people infected with the virus continues to rise exponentially.

Although most of these new infections are individuals who haven’t been vaccinated yet, among those new cases are individuals that have been fully vaccinated.

These cases are referred to as breakthrough cases.

The number of these breakthrough cases in places like Iceland and Israel where the majority of their populations are vaccinated is causing some alarm.

With social media awash with stories of vaccinated individuals contracting Covid-19 many are questioning the efficacy of the vaccines.

The rollout to the 300,000 Kiwis to book their jab comes five days earlier than expected.

1 NEWS spoke to two Kiwi scientists who specialise in immunology about why we are seeing those vaccinated contracting Covid-19 and why it’s still important to get vaccinated.

Clinical immunologist from Auckland Maia Brewerton says to start with, it’s important to understand how the vaccines work.

First of all, vaccines don’t directly kill the virus and no vaccine is 100 per cent effective.

Brewerton says breakthrough cases among vaccinated individuals were always expected.

“The vaccine works by teaching your immune system to stop or destroy the virus,” she says.

“However, the immune response to the vaccine is different from one person to the next.

“Many different factors may cause your immune response to be stronger or weaker such as overall health, age and medications.

“One study from the US demonstrated 44 per cent of breakthrough infections were amongst immunocompromised people – those with a weakened immune system.”

Although Covid vaccines may not make everyone 100 per cent immune from the virus, being fully vaccinated with Pfizer does make a person’s chance of getting infected with the Delta variant “much lower therefore you act as a roadblock to prevent the spread of the virus through the community,” says Brewerton.

“The Pfizer vaccine offers protection against all known variants of concern and an individual vaccinated with the Pfizer vaccine who develops a breakthrough infection with the Delta variant is far less likely to develop severe disease, hospitalisation or death.”

Brewerton says fully vaccinated people can still spread the virus if infected.

“However, if infected with the Delta variant these individuals appear to be infectious for a shorter period compared to the unvaccinated,” she says.

The CDC has stated around the world the greatest risk of transmission of the Delta variant is still amongst the unvaccinated.

How protected you are against the virus depends on the efficacy of the vaccine.

The only vaccine available to New Zealanders now is the Pfizer vaccine which is around 95 per cent effective against severe disease.

“That means that if 100 people were exposed to Covid, around five of them may still end up very sick in hospital with Covid,” Dr Nikki Turner from the University of Auckland explains.

“However, the majority of the others get no disease at all, or mild disease.

“The vaccine is also very effective against getting any illness at all, around 80 – 90 people vaccinated will not get any symptoms at all, but still 10 – 20 people may get some symptoms if they are exposed to Covid.”

Although the mRNA vaccine has the highest efficacy rate, there hasn’t been any clinical trials to directly say whether one vaccine is better than the other, Turner points out.

Does the Delta variant play a part those vaccinated contracting Covid-19?

Since the outbreak of Covid-19 back in 2020 there have been many variants of the virus, but one particular variant that has been able to take hold and become part of our daily vocabulary is the Delta variant.

The highly infectious Delta variant has caused concern about the risks emerging variants could have on the efficacy of the current Covid vaccines.

Brewerton says the Covid-19 landscape is constantly changing and new data comes out every week with experts here are watching closely.

She says although the Delta variant does make it easier for people, vaccinated and unvaccinated, to contract Covid-19, the chances of getting infected are “still far lower in the vaccinated population”.

“On the whole the variants do not cause more severe disease, but the big problem with the newer variants is they are better at infecting people,” says Turner.

“For countries where they still have very low rates of immunised people severe disease and death rates are going up again.

“For countries who have managed to get higher immunisation rates, rates of infection are again climbing, but due to having more immunised people, rates of severe disease and death are not as bad.”

Although we hear about vaccinated people testing positive for Covid-19, infection is still low among this group and far less likely to result in severe disease, says Brewerton.

“The bottom line is that the higher the vaccination rates in a community, the lower the total amount of disease will be,” says Turner.

* This article was first published on August 10 2021. The accompanying video was published on August 26.