With most Covid vaccines, one is considered fully vaccinated only after the second dose. A new study shows why the first dose is not enough to provide comprehensive protection against the coronavirus.
Anyone who has received the first dose of the coronavirus vaccine no longer counts. At least not as a person when it comes to meeting friends. Or as a household when it comes to contact restrictions, for example when visiting a restaurant.
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However, only people who have received both doses are considered fully vaccinated. Or those who have previously been demonstrably infected with Sars-CoV-2 and then vaccinated once. Apart from the vaccine from the US manufacturer Johnson & Johnson, all other Covid vaccines would require a second booster dose.
A new study shows that this is relevant in order to adequately protect the vaccinated against Sars-CoV-2.
Study shows: first shot does not protect against mutations
British scientists had determined in a study published in the journal “The Lancet” with 250 volunteers how high the risk of infection is after the first and second shot. To do this, they took blood from the test subjects who had already been vaccinated and examined the antibodies they contained.
They brought these together in the laboratory with the different variants of the coronavirus. The result: After a single shot, the antibodies were able to fight the wild type of Sars-CoV-2, which was originally isolated in Wuhan. Likewise, the variant, which had spread worldwide since the beginning of 2020.
However, it became problematic with the mutated variants:
For the variants Alpha (B.1.1.7) from Great Britain, Beta (B.1.351 ) from South Africa, and Delta (B.1.617.2) from India, the protection of the antibodies was no longer sufficient after receiving the first dose. It was too low to be able to fight and neutralize the virus.
“Even if a single dose still offers significantly higher protection than no vaccination, people who have been vaccinated only once are probably less protected against these Sars-CoV-2 variants,” write the authors, headed by study lead David Bauer.
British need to rethink vaccination strategy
Great Britain had pursued a vaccination strategy in which the first possible number of first vaccinations should be given. The second vaccinations, however, were postponed as far back as possible. According to the scientists, this approach must now be reconsidered – because the Delta variant (B.1.617.2) is particularly common in Great Britain. The scientists’ findings could therefore explain the renewed increase in new infections.
So far, according to the British Ministry of Health, around half of the British have been vaccinated twice against Corona, three quarters have received the first dose.
Partial immunization is a breeding ground for mutations
Data from Austria also show that partial immunization could be dangerous with regard to the mutations, which could even promote their development. In Tyrol, for example, the so-called B.1.1.7 + E484K variant, a combination of the alpha variant and an additional mutation, had spread.
As the Innsbruck virologist Dorothee von Laer told “Deutschlandfunk”, this had spread strongly after the first round of vaccination in the Schwaz district of Tyrol. Apparently, the partial immunization was a breeding ground for the variant outbreak.
Second dose as a “booster”
Infectiologist Christoph Spinner from Technische Universität München also confirmed the relevance of the second dose:
“The vaccination only provides complete protection if two vaccinations of the respective vaccine have been administered.”
This is the only way to examine the vaccinations in the clinical studies.
“And so we also know how to protect.”
However, there has so far been little experience with the single dose.
Accordingly, one should not rely on the initial protection.
“In any case, it is not so easy to find very good immunity to pathogens that can be transmitted by the respiratory tract,” explained the infectiologist.
We already know this from other pathogens, such as the real flu, influenza.
“That’s why we need this second vaccination. It brings with it a booster of the initially initiated training for the immune system.”
It is all the more important that people get their second shot. And that those who have recovered who have already survived the infection are vaccinated. For these, however, vaccination is initially sufficient.
“You can imagine it that way,” said the infectiologist, “the immune system was activated by the disease. The vaccination boosts it.”
It is not only important that the so-called neutralizing antibodies are produced in the immune system. Spinner added:
“The point is that they stay there long enough. The protective effect should not only last for days or weeks, but for many months or ideally years.”
Vaccination does not work immediately after the second vaccination
And beware: even after the second vaccination you are not protected immediately.
“The protective effect begins about 14 days after the first vaccination and then continues to build up. Complete vaccination protection is then about seven to 14 days after the second,” explained the expert.
At the moment, experts cannot yet say whether and how often a booster dose of the Covid vaccination will be necessary. Albert Bourla, the managing director of the pharmaceutical company Pfizer, said in April that a third vaccination with the Pfizer vaccine would probably be necessary for the fight against the pandemic.
Because of the mutations, among other things, this is the only way to ensure adequate immunity. Bourla also did not rule out an annual booster vaccination. Immunologist Carsten Watzl from Leibniz Research Center for Working Environment, on the other hand, stated that the entire procedure was not to be expected for the majority of the population.
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A dose per season, such as the flu vaccination, is only likely to be necessary for people with a weakened immune system.
For all others, the booster dose at intervals of several years would probably be sufficient.
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