CoronaVac: the results are satisfactory
The first inactivated coronavirus vaccine has passed the second phase of testing
Polina Loseva, N+1
The results of the 1/2 phase of trials of the CoronaVac anticoronavirus vaccine from the Chinese company Sinovac have been published in The Lancet magazine. This is the first vaccine based on inactivated viral particles, for which the results of the first phases of testing have become known. Apparently, it causes milder side effects than other vaccines. The vast majority of vaccinated participants formed neutralizing antibodies to the coronavirus, but how much they really protect against infection will become clear only in the third phase.
When the SARS-CoV-2 vaccine race started, all possible platforms on which a vaccine could be created went into action: "killed" and weakened viruses, their individual proteins and gene fragments, and even vectors based on other viruses.
So far, mRNA vaccines are leading the race - from Pfizer and Moderna, which recently published preliminary results of the third phase of trials and promised 90 and 94.5 percent effectiveness, respectively. Adenovirus vaccines are in second place: now the third phase is being developed by the Russian Center. CanSino, AstraZeneca, and Johnson & Johnson companies, as well as Gamalei.
However, there are questions for both technology leaders. The development of mRNA–based vaccines is a new and not yet fully developed method. At the same time, a viral gene is injected into the body so that human cells themselves produce a viral protein and introduce it to the immune system. But vaccines against other diseases that would act on the same principle do not yet exist, so it is difficult to predict what difficulties may arise with them.
Adenovirus vectors act similarly: a viral gene enters the body as part of a neutralized adenovirus, which infects human cells with this gene. This technology has been studied better, but it also has its controversial places: for example, it is unclear which adenovirus is better to take, and whether there will be an immune response to it that will prevent the vaccine from working.
Therefore, other companies continue to develop vaccines using long–established and proven technologies - based on neutralized SARS-CoV-2 particles. The first results of such tests appeared today. This is an inactivated (i.e. "killed") CoronaVac vaccine from the Chinese company Sinovac Life Sciences.
The vaccine developers presented the results of combined first and second phase trials. In total, 743 people took part in them – a sample comparable to similar studies of British and Chinese adenovirus vaccines, and much higher than the one with which researchers from the Center worked. Gamalei. All volunteers in the CoronaVac trials received two injections two or four weeks apart. At the same time, some got a placebo, others got a low dose of the vaccine, and others got a high dose.
According to the results of the first phase (143 people), side effects from vaccination occurred in less than a third of the volunteers (with the exception of one of the groups, where there were 38 percent of them). All of them were mild (most often limited to pain at the injection site) and passed within two days, except for one case when a research participant had urticaria, which was removed in three days. This distinguishes CoronaVac from other vaccines, which often cause fever in volunteers.
Also, in all groups of the first phase of trials, except for the one that received a placebo, the volunteers found antibodies to SARS-CoV-2 (up to 100 percent in different groups), including neutralizing ones – they were most in groups with a high dose of the vaccine two weeks after the second injection (up to 83 percent participants).
Moving on to the second phase, the developers changed the strategy of vaccine production: they switched from manual cultivation of cells with the virus to growing them in a bioreactor. At the same time, production has become more efficient, and the content of S-protein (to which antibodies are mainly formed) in the vaccine has almost doubled. Therefore, among the participants of the second phase, antibodies to coronavirus were even more common – up to 100 percent in some groups. And they had side effects no more often than in the first phase.
The organizers of the trials note several potential weaknesses of their vaccine. For example, there were no people from risk groups in their sample (they selected volunteers no older than 59 years), and they also did not track the T-cell immune response after vaccination (which, however, should not change much under the influence of an inactivated vaccine). In addition, the concentration of neutralizing antibodies formed in the volunteers was low: their titer ranged from 23.8 to 65.4. This is comparable, for example, with the results of the Russian adenovirus vaccine (49.3), but much less than in the blood plasma of people who have had COVID-19 – on average, 163.7. However, it is still unknown which titer provides people with protection from infection. The authors of the work also note that in tests on macaques, CoronaVac successfully protected animals from infection – so, perhaps, such a titer will be enough for people.
Based on their results, Sinovac experts considered that the vaccine is ready for the third phase of testing, which should answer all remaining questions about the effectiveness and protective effect. This phase has already started in Turkey, Indonesia and Brazil, almost 30 thousand volunteers are to take part in it. In Brazil, trials have now been suspended due to the suicide of one of the participants, but it is still unclear whether it is related to the effects of the vaccine.
In Russia, the inactivated vaccine is also being tested – the Chumakov Center is engaged in them.
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