How long does immunisation last with COVID-19 vaccines?

A lot of people are asking this question, and several studies have been done on the period of time antibody levels remain stable for each vaccine. 


The scientific community has become the point of reference the population looks to for answers, in this case on medicine. But the findings of the researchers are in many cases interpreted openly by people who don’t fully understand them. And that’s not all, blind faith in the researchers can lead people to expect solutions for things that science has no sure-fire answer to.

Nevertheless, to clear up some questions, all you really need is a little common sense. And some of the most common questions in recent months are on the immunity offered by vaccines: How long does the immunity offered by each vaccine last?

How do the antibodies evolve and when do they stop offering an immune defence?

At the moment, the decreasing numbers of new infections proves the vaccines are effective, but the duration of this effectiveness will only become clear when vaccinated people develop symptoms showing they’ve become infected by COVID-19 again.

To answer the first question, it’s important to remember that if you’ve been vaccinated, this protects you from the symptomatic disease called COVID-19, but you can still become infected by the virus. This has been proven by some people who were infected after being vaccinated, although in very few cases and they developed mild symptoms. What’s more, immunity depends on many different factors such as sex, age, clinical history and other physical characteristics, so it’s different from person to person.

Currently, to find out more about the duration of the effect of antibodies after vaccination, studies are being done on people who have been vaccinated, monitoring their level of protection to watch for any signs of vulnerability when the level of antibodies drops off, starting two weeks after the jab, which is when immunisation is considered to be optimal.

But the above gives rise to another question. How does the immunity offered by each vaccine evolve?


How long does immunity last with Pfizer?

What we all know as the Pfizer vaccine is actually called the Comirnaty vaccine. It’s produced by the German BioNTech and American Pfizer labs. It was the US that first approved its use, on 11 December 2020, 10 days before it was approved by the European Union.

US healthcare workers were the first people to be vaccinated. The United States Centers for Disease Control and Prevention (CDC) did a meticulous study finding that immunity in people vaccinated lasted over three months.

There are two things worth remembering with this result: the first is young average age of the professional health workers vaccinated; the second is that the results considered people who had just had one single jab at that point and, some had been vaccinated with the Moderna vaccine. 

According to Ugur Sahin, the co-founder of the BioNTech laboratory, the number of antibodies starts to decrease six months after receiving the second dose of the vaccine. That’s why, to guarantee people remain protected, it’s recommended they get a third jab 9 – 12 months after the second one.

Currently no investigator outside Pfizer/BioNTech has verified this information, but as updated first-hand data become available, it would appear to be reliable.


How long does Moderna protection last?

Moderna was the second vaccine to be approved in the US and Europe. It was developed by the North American laboratory of the same name and is based on messenger RNA (mRNA) just like the Comirnaty vaccine.

A study published in the New England Journal of Medicine on the first 33 people in the world to be vaccinated with Moderna, detected a high level of antibodies six months after the second dose of the vaccine. While the level of immunisation was significant in all those who received the vaccine regardless of their age, people over 56 years of age had slightly fewer antibodies than people under 56.

After nine months however, the activity of the antibodies dropped off in a more notable way. This is why the initial good results didn’t stop Dan Staner, the vice chairman of Moderna in Europe, acknowledging the possibility of needing a third dose six to twelve months after the second jab. Another reason for this is that the South African Beta variant of the virus reduces immunisation by a factor of 6 – 7.


How long do the AstraZeneca antibodies last?

AstraZeneca is the laboratory which, with Oxford University, developed the Vaxzevria vaccine, approved by the European Medicines Agency (EMA) on 29 January 2021. A few months later, there was great cause for concern when the EMA issued an assessment report on its safety and effectiveness after certain cases of thrombosis associated with the vaccine.

Along with other data, the report compared the number of lives saved by the vaccine to the number of deaths caused by blood clots, one of this vaccine’s most severe side effects. The conclusions showed that the balance was for the most part positive.

Likewise, the EMA estimated a vaccine effectiveness of 80% during the first four months, in people who had been fully vaccinated. 

Unlike the other vaccines, the second dose of Vaxzevria is administered 4 – 12 weeks after the first jab. This is because, according to a study, delaying the second jab by 12 weeks increases the effectiveness of the vaccine. That’s why the second AstraZeneca jab is administered after this period of time. 

In Spain, the second jab is administered four months later, as this is when the action of the antibodies starts to diminish. As the first vaccines were administered in February, there are still no results for the studies on how long the protection with the Vaxzevria vaccine lasts.


How long does the protection with the Janssen vaccine last?

Janssen, developed by Johnson & Johnson, is the most recent vaccine approved in Europe and the United States on 11 March this year. It’s a single-dose vaccine, and the immunity this vaccine offers could have been quickly verified.  

In the United States however the authorities decided to monitor the risk of blood clots with the vaccine, which caused some delay and showed there was minimal risk; the first major batch of Janssen vaccines reached Europe in April. Vaccination was therefore delayed until the beginning of May and as a consequence those who have been vaccinated with Janssen have only been protected for a month and a half to date.

The laboratory that created the vaccine lost no time in running a clinical trial however, which was published in the New England Journal of Medicine. 805 vaccinated people participated for 71 days after vaccination. In both young adults and people over 65, antibody levels remained high and stable.

As for the messenger RNA vaccines (Pfizer and Moderna) we’ll only know with a greater degree of certainty whether a third dose is necessary to guarantee full immunity, as the two labs have said, after summer.

We’ll have to wait a bit longer for AstraZeneca and Janssen, both based on adenoviral vectors. Towards the end of the year, it’s expected we’ll know how resistant the antibodies are and whether or not more doses are required.

Remember, it’s important to use an antibody test, like the Test, so you and others can check their antibodies a while after being vaccinated, or after recovering from COVID-19. Considering the uncertainty about how long vaccine immunity lasts, it’s more important than ever to know, first hand, how protected we are against the virus at all times, and know whether we’ll need additional protection in the future.