The polio vaccine thing

Polio is polio, Commonly known as polio, The clinical manifestation is lifelong disability, Seriously affecting human health. Four doses of polio vaccine can prevent polio. Through continuous polio vaccination, Most countries have eradicated polio. According to the World Health Organization, After the successful eradication of smallpox, the second infectious disease to be eradicated by human beings will be polio. Therefore, the World Health Organization has launched the “Polio Free Initiative” worldwide, requiring every country to implement vaccination to eradicate polio, and eventually eliminate wild polio virus from the earth, so that human beings will no longer have to be vaccinated against polio.

First, how to choose polio vaccine?

1. Two technologies for polio vaccine

A. Deactivation process

That is, to eliminate the vitality of wild polio virus and make it a vaccine virus that can infect human body but will not cause poliomyelitis. Vaccines containing live vaccine virus are polio reduced live vaccines.

B. inactivation proces

The polio virus is killed and made into a vaccine. The vaccine does not contain live virus, but it can still cause the body’s immune response and generate resistance to polio virus.

2. Current vaccination procedures

The two vaccines have their own advantages and disadvantages, which leads to the global eradication of polio is not an overnight thing. Under the current situation that free live reduced vaccine and inactivated vaccine at one’s own expense coexist, how to choose has certain attention.

A. Direct inactivated vaccination

Globally, some countries directly use inactivated vaccine to inoculate 4 doses, which can solve the safety problem, but the cost is too high.

B. Sequential procedures

There are also many countries that adopt the scheme of inactivated vaccine first and reduced live vaccine later, which is called sequential procedure.

The sequential procedure is based on: Vaccine-associated paralysis usually occurs on the first vaccination, If the inactivated vaccine is used in the first 1 ~ 2 doses, the human body can produce certain immunity, and then the reduced live vaccine will not cause [vaccine-related paralysis], which will also help to improve the local immunity of digestive tract and reduce the cost. If you are curious about [vaccine-related paralysis], please continue reading.

The implementation effect of this sequential procedure is indeed quite ideal, which can effectively avoid the occurrence of vaccine-related paralysis and save the cost.

3. Individual suggestions based on national conditions

Personally, I think that based on the current supply of polio vaccine in our country, the first two doses of inactivated vaccine at one’s own expense and the second two doses of free reduced live vaccine may be the most cost-effective solution at present.

For those who have already used the reduced live vaccine, if there is no vaccine-related paralysis with a probability of 1/250,000, the possibility of vaccine-related paralysis can be ruled out if they continue to use the reduced live vaccine.

For those who have already used the reduced live vaccine, it is not necessary (not impossible) to use a separate inactivated vaccine, but the pentavalent vaccine containing inactivated vaccine components is still worth recommending.

Second, the merits and demerits of polio attenuated live vaccine

On 7 October 2014, foreign media reported a roadside bomb terrorist attack on the vehicle of polio vaccinators in Pakistan. This is not the first time such an incident has occurred in Pakistan: in April 2013, a police officer escorting polio vaccinators was shot dead; In January 2013, two polio vaccinators were killed in a bomb attack. In December 2012, at least eight people involved in polio vaccination were shot dead.

Pakistan is one of the few countries in the world where wild poliovirus is still prevalent. Due to its special national conditions, it is difficult to vaccinate every child with 4 doses of polio vaccine through routine and orderly vaccination services. Pakistan’s vaccinators have to carry out 8-10 times of polio vaccine booster immunization every year to ensure that every child can receive sufficient doses of polio vaccine.

Many children receive far more than four doses of polio vaccine during multiple rounds of booster immunization. This is not necessary, but only in this way can the polio epidemic caused by missing seeds be avoided to the greatest extent. This multiple rounds of booster immunization and terrorist hatred of vaccination have led to the extremely high risk of attack on polio vaccinators.

Pakistan’s vaccinators are risking their lives to get vaccinated against polio, which shows that the World Health Organization’s polio-free campaign has received strong support from all countries. The biggest obstacle to the real success of the polio-free campaign is not that vaccination in some countries is difficult to carry out, but that the vaccine itself is not perfect.

1. Deficiencies of live polio vaccine

A. Vaccine-associated paralysis

Children in our country are vaccinated free of charge with live reduced polio vaccine, And make it into sugar pills, It is more convenient for children to take orally, This is what people often call “sugar pills”. Sugar pill vaccines play a key role in achieving the global goal of polio-free, but they have a serious adverse reaction that is increasingly apparent-very few people will suffer from polio-like limb paralysis after vaccination. This limb paralysis has been confirmed worldwide and is named “vaccine-related paralysis”.

According to World Health Organization estimates, The probability of vaccine-related paralysis is about 1/250,000. Live attenuated polio vaccine is usually administered in 4 doses. The majority of vaccine-related paralysis occurs in the first dose, The probability of 1/250,000 refers to the risk of the first dose. Sometimes, when people calculate this probability, they take all 4 doses as denominator, and the result is about 1/1 million. About 16 million children are born every year in our country, and about 64 people are vaccine-related paralyzed. Although this is not a big number, it is undoubtedly a tragedy for the families of these children.

Vaccine-related paralysis is a serious adverse reaction of polio attenuated live vaccine, and its absolute incidence rate is very low. However, once it occurs, the limb paralysis of patients is almost lifelong.

B. Vaccine-derived virus

In addition to vaccine-related paralysis directly caused by vaccine viruses, there is also a rare but highly concerned problem of polio attenuated live vaccine-polio attenuated live vaccine will be discharged into the external environment after reproduction in human body, and live vaccine viruses have the possibility of gene mutation in some immunocompromised people and in the external environment.

The mutated vaccine virus will atavate to a highly pathogenic poliovirus, posing a threat to susceptible populations. This poliovirus atavated by vaccine virus is called [vaccine derived virus].

Cases caused by vaccine-derived viruses have been confirmed worldwide, These cases usually occur in areas where the vaccination rate of polio vaccine is low and there are a large number of susceptible populations. At present, The problem of vaccine-derived virus is not serious yet. China is vaccinated with tens of millions of doses of reduced live polio vaccine every year, and only a few cases of vaccine-derived virus have been found. However, the consequences are exactly the same as the symptoms after polio virus infection, leaving permanent disability.

In the long run, if human beings want to eradicate polio through vaccination like smallpox eradication, they must stop using live polio vaccine.

As long as the live polio vaccine is used for one day, the shadow of vaccine-derived virus will exist for one day, and it will never be possible to eradicate polio.

2. Advantages of attenuated polio vaccine

Inactivated polio vaccine can completely avoid the above two major defects. It is reasonable that all countries should immediately stop using reduced live polio vaccine and switch to inactivated vaccine, but many countries in the world still continue to use reduced live polio vaccine.

The reason is that compared with inactivated polio vaccine, reduced polio vaccine has the following advantages.

A. Low production costs

Polio attenuated live vaccine uses live vaccine virus to reproduce in human body to stimulate human body to produce immunity, so only a small number of vaccine virus is needed as seeds to achieve good results.

Inactivated polio vaccine needs to rely on these inactivated polio virus corpses to stimulate the body’s immunity. Of course, the stimulation intensity and fidelity are not as good as those of live viruses, and its efficiency in stimulating the immune system is not as good as that of reduced live vaccines. Therefore, many polio virus corpses are needed to achieve satisfactory results.

Generally speaking, the amount of virus producing 100 doses of polio vaccine is only enough for 1 dose of inactivated polio vaccine. In other words, the production cost of inactivated polio vaccine is at least 100 times that of inactivated polio vaccine.

Even if not from the production cost but from the production capacity, if the original one enterprise produced live polio vaccine, it could meet the local demand for live polio vaccine. After changing to inactivated vaccine technology, 99 more enterprises or 99 times more production capacity will be needed to meet the demand for inactivated vaccine, which is also very difficult to realize in the short term.

B. that inoculation operation is simple

Polio attenuated live vaccine is most commonly made into sugar pills, which are convenient for children over 1 year old to take. Infants and young children are crushed and fed. In addition, there is a liquid drop, which is simpler to use and only needs 2 drops. Generally speaking, oral polio attenuated live vaccine does not need vaccination devices and can be operated by non-professionals or parents.

Inactivated polio vaccine is injection type and must be used by trained medical personnel to complete the vaccination. In this sense, the vaccination cost of reduced live vaccine is also lower.

C. Immune effect is slightly better

The mechanism of action of polio attenuated live vaccine is that live vaccine virus reproduces in human digestive tract to stimulate human immunity, which includes both systemic immunity (common antibodies existing in blood) and local immunity (secretory antibodies existing in digestive tract).

Inactivated polio vaccine cannot reproduce in human digestive tract, so it can only stimulate human body to produce systemic immunity.

D. High efficiency in establishing population immunization barriers

Live attenuated polio vaccine will be discharged from the body after reproduction in the digestive tract, These vaccine viruses discharged from the body may immunize the surrounding population through recessive infection. Even if people around people vaccinated with live polio vaccine are not vaccinated with the vaccine, they may acquire immunity through this way, enabling the whole population to establish a high level of immune barrier.

Inactivated polio vaccine cannot be reproduced and discharged from the body, and its preventive effect is limited to the recipient himself.

Third, can China finally eradicate poliomyelitis?

The above carefully analyzed the advantages and disadvantages of the reduced polio vaccine and the inactivated polio vaccine. In summary, If a country is not short of money and has strong vaccine production capacity, then it must choose inactivated polio vaccine. However, there are many countries in the world that are short of money and do not have their own vaccine industry, which makes [inactivated polio vaccine instead of reduced live vaccine] a gradual process.

China is not unaware of the benefits of inactivated polio vaccine, but it still chose reduced polio vaccine, which is determined by China’s national conditions.

However, things have turned for the better. In 2009, China has approved an imported polio inactivated vaccine product to go on the market. In 2010, another imported pentavalent vaccine product containing inactivated polio vaccine components was approved to go on the market. These inactivated polio vaccine products are all used in China as self-funded vaccines, giving the public an important choice in addition to the free reduced live vaccine.

At the same time, China’s domestic inactivated vaccines have also stepped up research and development, It is expected to be listed around 2015. Once the production of domestic inactivated polio vaccine reaches the ideal level, China is likely to include it in the scope of free vaccines, which will truly solve the problems of vaccine-related paralysis and vaccine-derived viruses and provide the most powerful weapon for the final eradication of polio in China.