In the 1970s, Japanese scientist Takahashi and his colleagues isolated a virus from a specimen of a boy suffering from natural chickenpox. After several times of attenuated culture, the obtained virus was named Oka strain and became the standard virus strain for varicella vaccine production in the world. Oka strain varicella vaccine has been used worldwide for more than 30 years, and its safety and effectiveness have been widely confirmed.
I. Both domestic and imported varicella vaccines are Oka strains
The domestic varicella vaccine was first produced by Shanghai Institute of Biological Products imported technology from Japan. In 2000, there were also imported varicella vaccines from SmithKline Company. After that, many vaccine enterprises in our country began to produce and supply varicella vaccines, all of which were Oka strains. At present, there are 4 kinds of domestic varicella vaccines and 1 kind of imported varicella vaccine on the market in our country.
Second, one dose of varicella vaccine is not enough?
For children aged 1 to 12 years old in our country, only one dose of varicella vaccine is recommended at present, and as the second type of vaccine, it is voluntarily vaccinated at one’s own expense. After years of large-scale vaccination, researchers found some abnormal phenomena in the outbreak of varicella in some kindergartens and schools:
1. Even if the vaccination rate reaches 100%, the outbreak of chickenpox cannot be prevented. A considerable number of children who have been vaccinated against chickenpox have developed the disease, accounting for sometimes more than 50% of the total number of cases.
2. With the passage of time after vaccination, the protective effect of the vaccine gradually decreases, reaching 100% in the first year after vaccination and 51% in the sixth year after vaccination.
It seems that the protective effect of one dose of varicella vaccine vaccinated according to the standard procedure is far less than that of other vaccines vaccinated according to the standard procedure. Foreign studies also show that the protective effect of one dose of varicella vaccine is not as good as expected.
Studies show that the protective effect of those who have received 2 doses of varicella vaccine is obviously better than that of those who have received 1 dose. There is no difference in the protective effect between domestic varicella vaccine and imported varicella vaccine. Even so, the good news is that even if people who have been vaccinated with varicella vaccine suffer from varicella, their condition is milder than that of those who have not been vaccinated with varicella vaccine.
Three, two ways to improve the inoculation effect
How to improve the vaccination effect of varicella vaccine is a problem that researchers have to face. At present, there are two solutions: the first is to increase the content of virus in varicella vaccine; The second is to change the recommended inoculation times for children from 1 dose to 2 doses.
1. Increase the content of vaccine virus
The level of virus content in varicella vaccine has a great relationship with the final protection effect. China’s latest pharmacopoeia (2010 edition) has not yet included varicella vaccine, so it can be considered that there is no national standard for virus content in varicella vaccine in China at present.
Since when Shanghai Institute of Biological Products first produced varicella vaccine (2000), the enterprise standard for the virus content declared by Shanghai Institute of Biological Products was not less than 2000 PFU/dose (PFU is a virus measurement unit), [not less than 2000 PFU/dose] has become the current and unofficial virus content standard for varicella vaccine in China.
In principle, On the premise of safety, Increase the virus content of the vaccine, It should be possible to improve the immune level of the body after vaccination, so [not less than 2000 PFU/dose] is only a starting point. A few years ago, SmithKline Company publicized that although the registration standard of its varicella vaccine is [not less than 2000 PFU/dose], its actual virus content has reached [10,000 PFU/dose], and showed evidence that the protective effect of high-dose varicella vaccine is better than that of low-dose vaccine.
As that varicella vaccine is preserve between 2 and 8 degrees Celsius, Its virus content will gradually decrease, and high-dose varicella vaccine can ensure its maintenance of a relatively high virus content within the validity period. The concept of high-dose varicella vaccine has been accepted by domestic varicella vaccine manufacturers. At present, the measured value of virus content of domestic varicella vaccine is generally above 10,000 PFU/dose, and some enterprises have already exceeded 20,000 PFU/dose.
2. Change to 2 doses of inoculation
Increasing the number of doses may be a better idea than increasing the virus content in the vaccine. Since 2007, the United States has adjusted the standard vaccination procedure for varicella vaccine to 2 doses: 1 dose each for 12 to 15 months old and 4 to 6 years old. Europe also announced at the same time that it would give priority to recommending 2 doses of varicella vaccination procedure as long as financial resources and service capacity permit.
Foreign studies show that the main advantages of 2 doses of inoculation are: further reducing the incidence and complications of varicella; Reduced the number of susceptible persons; The possibility of re-illness after vaccination is lower. The risk of chicken pox outbreak is reduced; The protection period of varicella vaccine was prolonged.
Fourth, better cost-benefit ratio
The vaccination strategy of two doses of varicella vaccine can not only reduce the incidence of varicella, but also reduce the outbreak of varicella in schools and other collective units, reduce social public health problems and reduce the overall disease burden of varicella in China.
China has carried out research on the two-dose vaccination procedure of varicella vaccine. It can be expected that in the near future, China will also start the 2-dose vaccination procedure of varicella vaccine. If the domestic varicella vaccine can slightly reduce some virus content at that time, such as leaving the factory according to the standard of [5000 PFU/dose], then the production of varicella vaccine can theoretically double, and its retail price will drop to less than 100 yuan/dose, which is definitely good news for the public.
Author: Vaccines and Science