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The CoronaVac vaccine may be effective for immunocompromised individuals

SARS-CoV-2 has infected more millions of  people. Brazil has been the most affected country with more than 15 million cases and more than 430 000 deaths. Vaccines have allowed us to greatly reduce mortality rates, and amongst available vaccines, the CoronaVac (also called Sinovac), developed in China, is the only one to use the traditional technology of “inactivated” vaccines: the complete virus is present in the vaccine, but chemically neutralised so as to prevent it from replicating in the organism. This is not the case with other vaccines, which use only the spike protein to stimulate the organism’s immune response. We can only hope that the technology using the whole virus remains effective against variants.

The CoronaVac vaccine has been approved by the WHO (World Health Organisation) and authorised in several countries such as Brazil, China and Turkey. It represents, for example, 75% of total vaccinations in Brazil. It can even be stored at 4°C, unlike mRNA vaccines that need to be frozen, facilitating distribution in developing countries. But how effective is it really, compared to other vaccines? One way of answering this is to study its effect on vulnerable individuals, such as people who are immunocompromised. Brazilian researchers (at the Universidade de Sao Paulo) have studied its safety and efficacy in such people, who are at greater risk of infection and of developing serious forms of the illness.

The researchers carried out a study using vaccination data from a centre in Brazil, on a cohort of 859 immunocompromised patients with auto-immune rheumatic disease, compared with a control group of 179 non- immunocompromised patients. All individuals received 2 doses of the vaccine.

They firstly checked the presence of neutralising antibodies 6 weeks after injection of the 2nd dose. In immunocompromised individuals, the level of neutralising antibodies was lower than in the control group (56% of these individuals had developed antibodies compared with 79% of the control group). Then researchers analysed levels of IgG anti-SARS-CoV-2 antibodies, 28 and 69 days after the 2nd injection. On average, immunocompromised patients had lower levels of IgGs than the control group.

While these first results were intuitive, did any side-effects occur? Tolerance and safety issues are of paramount importance for this group, because the vaccine does contain an adjuvant (aluminium salts). Such adjuvants can provoke or aggravate symptoms in auto-immune pathologies. In this study, no moderate or severe side-effects were noted in the short-term. Minor effects, most often occurring in both groups, included pain at the injection site, head-aches and drowsiness. However, the researchers did observe more minor side-effects in the immunocompromised group, including arthralgia (joint pain), back pain or other discomforts.

The scientists then studied individuals 40 days after their vaccination. They reported that in total, 39 had been infected by SARS-CoV-2, with no significant difference between the immunocompromised and the control groups.

This study of the use of CoronaVac on immunocompromised individuals in important because this group has up till now been excluded from phase 3 clinical testing, although these patients are high-risk. The scientists showed that vaccination enables a reduced though acceptable level of production of antibodies in these patients, without moderate or severe side-effects. This vaccine may therefore be suitable for this group. However, the study did not analyse its efficacy in the long-term. A study of symptomatic cases over 12 months is currently being carried out.

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