Luka Cicin-Sain: Getting a flu shot and the Corona booster: Does it make sense?

The cold season has arrived along with the question of whether a vaccination against influenza makes sense in times of the ongoing pandemic. And when is the right time for the third vaccination, i.e. the booster vaccination against Covid-19?

The Robert Koch Institute (RKI) already issued a recommendation for the Corona booster for everyone aged 18 and over. "Get both!" Prof Luka Cicin-Sain, a vaccination expert from the Helmholtz Centre for Infection Research in Braunschweig recommends. In his words, our immune system can be compared to a weary "football team in the second half-time" and both vaccinations are akin to "introducing substitute players with fresh legs to improve the defence squadron."

How much sense does a flu shot make in times of the Corona pandemic?
The flu shot continues to be important and is recommended. Especially for certain at-risk groups, the flu shot is essential - and this has not changed at all during the Corona pandemic. On the contrary: In these times the flu shot has become even more important because the threat of influenza is still here, but healthcare resources are tight because of Corona.

Do we really need protection from the flu? There were hardly any flu cases last year, after all.
You cannot assume that there is less of a risk of catching the flu this year. Especially the infection control measures that were taken, from spacing and mask-wearing to working at the home office, were the reasons why we had fewer flu cases. While this continues for the moment, the pathogen is still amongst us and it has a well-known seasonality. So we should continue to protect ourselves as well as we can.

If I haven’t even been able to make up my mind on a first Corona shot, does it still make sense in the current situation?
Absolutely. It is never too late because you don’t know when you’re going to get infected. The longer you wait, the higher is the likelihood of encountering SARS-CoV-2 and doing so without protection from vaccination. It is important to note, though, that no vaccination protection is established in the first week and a half after the first dose, and it takes two weeks after the second dose for full protection.

In light of high Corona infection rates, experts emphasise the significance of the so-called booster shot. What exactly happens in the body?
Memory B-cells and plasma cells that generate antibodies initially receive signals for replication and survival and expand in number. As the signal from the antigen recedes, these molecular signals go down. The cells stop dividing and many of them die. This is useful to make room for other immune cells against other threats, but over time the amount of antibodies slowly goes down. The booster shot gives a new impulse to these cells to expand their numbers again.

What vaccines are available for the booster vaccination in Germany?
There are four vaccines approved in Germany to date, two mRNA-based ones from BioNTech and Moderna and two adenovirus-based ones from AstraZeneca and Janssen. In general, all of these vaccines provide effective and sustained protection against Covid-19-related severe illness and death with the mRNA vaccines being a little better. Vaccination also protects against SARS-CoV-2 infection and thus also reduces the risk of transmission from vaccinated persons to their contacts. But it has been evident that the protection conferred by the vaccine declines over time. At older age, the overall immune response after vaccination is lower and declines more rapidly. This increases the risk of breakthrough infections, which can also lead to severe courses of disease more frequently. The booster vaccination is done with an mRNA vaccine no earlier than six months after completion of the basic immunisation. The RKI recommends an additional dose of mRNA vaccine especially if a person was originally vaccinated with the Covid-19 vaccine from Janssen because, relative to the number of vaccine doses given in Germany, most vaccine breakthroughs are observed in persons vaccinated with Janssen's vaccine.

Can at-risk groups receive the influenza and Corona vaccines at the same time?
From an immunological point of view, there is no reason to avoid this. Our immune system is exposed to many pathogens every day - that means many “enemy contacts” per day. The same happens to the body with the dual vaccinations which simulate two different pathogen infections. The immune responses may even reinforce each other. The dual vaccination is best done at two different sites, for example on the right and left upper arm, at the same time. Because the immune reaction commences locally and matures in regional lymph nodes. Consequently, two groups of lymph nodes can be challenged independently of each other. Yet, the recipient may have two sore arms at the same time and be impaired on the day after the immunisation.

Do you get the same or more severe side effects with a booster shot than with the first two Corona vaccinations?
In essence, any vaccination is expected to trigger an immune response. Obviously, that may be accompanied by side effects. The side effects after vaccination include pain at the injection site and fatigue, more rarely fever and chills. These symptoms last a day or two, very rarely longer. Very rare - less than 1:10,000 - are immune reactions such as myocarditis, but these improve after a few days without late effects. Thrombosis (1:100,000) was even less frequent after vaccination with AstraZeneca or Janssen. Allergic reactions are extremely rare, with two to five cases per one million vaccinations. But known allergies to drugs or pollen do not pose an increased risk that there will be an allergic reaction to the vaccine. Assuming that the consequences of Covid-19 infection are life-threatening in about one per cent of the cases, the risks are clearly associated with the infection rather than the vaccination. Overall, the data collected on the booster to date show that its side effect profile is equivalent or at least no worse. It’s definitely not true that it gets worse the more often you get vaccinated.

When is the ideal time for the third vaccination?
The ideal time for the booster vaccination is six months after the second shot. I would recommend to get a booster in any case. If there is suspicion of possible allergy to components of the vaccine, you should talk to your family doctor, but that is just about the only significant group for which vaccination is not approved. Recipients of immuno-suppressing drugs, such as autoimmune patients or organ recipients, absolutely need the third dose because their immune system does not defend them adequately and needs all the help it can get. To protect this group of people, it is important that family members as well as co-workers who they are exposed to every day, get their vaccination done, thus providing a so-called “ring vaccination”.

Does an antibody test make sense to decide whether a third vaccination is even needed?
Actually, the antibody test against Corona is only a guide that indicates the presence of antibody, but not a conclusive statement about actual protection. This is the case because antibody levels in the test do not necessarily reflect the antiviral performance of the tested person. Unfortunately, a quantitative test detecting the level of immune protection is not available yet. A lot more research is needed here.

Interview: Susanne Thiele

Published: December 2021

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