What does science say about the combination of different Covid-19 vaccines?

From Germany to the Dominican Republic, government medical authorities are recommending mixing vaccines of different technologies (one in the first dose and one in the second) in the hope of achieving more effective protection.

But does this strategy really offer a more powerful immunization and is it necessary? From a scientific perspective, there is no answer yet. Studies are underway to better understand the risks and benefits of mixing Covid-19 vaccines — which could alleviate logistical problems for some immunization programmes. But more research is needed to answer whether the mixture works in the real world.

On Friday (2), Germany issued the most accurate recommendation on mixing vaccines. The German Standing Committee on Immunization (STIKO) said last Thursday (1) that people receiving the first dose of the Oxford AstraZeneca vaccine “should receive the RNA vaccine as a second dose, regardless of their age”.

The Pfizer and Moderna vaccines use messenger RNA (mRNA), while AstraZeca is made from a virus called adenovirus. According to STICKO, the results of current studies show that the immune response from this combination of vaccines is “manifestly superior”.

Dominican Republic authorities said Thursday (1) that they will begin providing health professionals with the third dose of the vaccine, a booster dose to contain variants, and that these people will receive vaccines different from those they took in the first dose. AtraZeneca, Sinovac and Pfizer vaccines are available in the country.

In June, the Canadian National Advisory Committee on Immunization made a less robust recommendation when it stated that “mRNA vaccines are preferred as a second dose for individuals who have taken the first dose of AstraZeneca.”

The Canadian commission says it made the recommendation based on “emerging evidence of an improved immune response to the vaccine mixture”.

Vaccination schedules that mix the AstraZeneca and Pfizer vaccines stimulate a strong immune system response, however, the response to two doses of Pfizer has been shown to be stronger, according to UK researchers.

In another study also done in the UK, people who received a different type of vaccine as a second dose had more side effects such as fever, chills, fatigue and headache. But these effects were transient and did not pose any concerns about the safety of the vaccination.

second generation vaccines

He said that the idea of ​​using different vaccines for the first and second doses had been explored before – before the novel coronavirus pandemic – CNN Researcher Amesh Adalja, of the Johns Hopkins Center for Health Security, the concept is called a heterogeneous booster dose and has already been used to study bird flu, according to Adalja.

He says it’s too early to say whether it will take months or years to know what future Covid-19 vaccines will look like. But it is important to understand how second-generation immunity is made, to use this knowledge for other vaccines against different infectious diseases, and to understand how the immune system responds differently to different vaccines.

For the researcher, this is a very promising area of ​​research, and it could help to develop better immunization programmes, especially for people who do not have good immune responses, such as immunosuppressed patients who have undergone organ transplants.

A study published in June in the Annals of Internal Medicine suggests that a third dose of the coronavirus vaccine may help boost antibody levels in people who have had organ transplants who haven’t had strong responses to a standard vaccination schedule.

No need to backup yet

With the most contagious delta variant prevalent in the United States, many people worry that they may need to receive a third dose of the vaccine to stay protected — especially those who have taken the Janssen vaccine, which is considered less effective.

But new research results indicate that the Janssen vaccine appears to adequately protect against the delta variant, the company said in a statement Thursday evening. The immunizing agent provides protection that lasts at least eight months.

“Current data from the eight-month study to date shows that the single-dose Covid-19 vaccine from Johnson & Johnson generates a robust neutralizing antibody response that does not diminish; instead, we see an improvement over time.” and development at Janssen, the vaccine arm of J&J, in the statement.

The company said that a single dose of the vaccine elicits a long-term antibody response and generates immune system cells called T cells, which also last for eight months. “The results indicate that there is no need for a booster dose at this time,” he said. CNN Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia.

We must be guided by science. Currently, science tells us that two doses of the mRNA vaccine or a single dose of the Janssen vaccine protect against severe forms of the disease caused by the delta variant.”

Contributing to this report are CNN reporters Niamh Kennedy and Naomi Thomas

(Translated text. Read the original text in English)