Between Preventing Disease and Preventing Infection 

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Sometimes in the late 1970s or thereabout, when Nigeria was confronted with its protracted and problematic national question, the iconic Sonny Okosun, released a song, Which Way Nigeria? In the lyrics of the song Okosun boldly declares, ‘’I love my fatherland’’. The issues the late musician raised are still begging for answers.

Though this piece is not about the musician, but it might interest some readers to know that he was born on January 1, 1947 and transited May 24, 2008 in Washington DC. He was from Edo State, and was best known as the leader of the Ozzidi band. He named his band Ozzidi after a renowned jaw river god, which to Okosun means “there is a message“. According to Wikipedia, his surname is sometimes spelled Okosuns and his first name Sunny. He was one of the leading Nigerian musicians from the late 1970s to mid-1980s.

‘’Okosun’s brand of African pop music, Ozzidi, is a synthesis of Afro-beatreggae and funk music. From 1977, he became known for protest songs about Pan-Africanism, freedom and a few other social and political issues affecting Africans’’, Wikipedia says.

As a young boy, Okosun spent his early childhood with his grandmother at Ibore, near Irrua in Edo State, thereafter, he moved to Enugu to live with his parents and where his father worked with the Nigerian Railway Corporation.

 Okosun attended various training schools starting with St Brigid’s School, Asata, Enugu before enrolling at a government trade centre in Enugu. He left the training centre before completing his studies. Excited by a career in entertainment, he travelled to Lagos to further his interest in acting. In Lagos, he took drama lessons at a drama school in Surulere but left after a few months returning to Enugu.

In Enugu, he found opportunity in small roles where he participated in a few dramatic productions; he also worked with a notable Enugu drama studies teacher, professor John Okwerri. His participation in Okwerri’s group and his determination to succeed in entertainment led him to be featured in some radio and TV skits with the Eastern Nigeria Television Station

Back to where we were heading to. Those who know better say there is a fundamental difference between preventing disease and preventing infection. A vaccine like that of COVID-19 that “just” prevents disease might not stop people from transmitting the disease to others—even if they feel fine.

But a vaccine that provides sterilising immunity stops the virus in its tracks.

Vaccines are however, a marvel of medicine. Few interventions can claim to have saved as many lives. But it may surprise some of us to know that not all vaccines provide the same level of protection. Some vaccines stop patients/non-patients from getting symptomatic disease. Others stop people from getting infected.

Experts say the latter is known as “sterilising immunity.” With sterilising immunity, the virus can’t even gain a toehold in the body because the immune system stops the virus entering cells and replicating.

It is being argued that in an ideal world, all vaccines will induce sterilising immunity. In reality, it is actually extremely difficult to produce vaccines that stop virus infection altogether. Most vaccines that are in routine use today do not achieve this. For instance, vaccines targeting rotavirus, a common cause of diarrhea in infants, are only capable of preventing severe disease.

But this has still proven invaluable in controlling the virus. In the US, there has been almost 90% fewer cases of rotavirus-associated hospital visits since the vaccine was introduced in 2006. A similar situation occurs with the current poliovirus vaccines, yet there is hope this virus could be eradicated globally.

The first SARS-CoV-2 vaccines to be licensed have been shown to be highly effective at reducing disease. Despite this, researchers don’t yet know whether these vaccines can induce sterilising immunity. It is expected that data addressing this question will be available from the ongoing vaccine clinical trials soon. Although even if sterilising immunity is induced initially, this may change over time as immune responses wane and viral evolution occurs.

Lack of sterilising Immunity

What will a lack of sterilising immunity mean for those vaccinated with the new COVID vaccines? Quite simply, according to scientists, it means that if one encounters the virus after vaccination, he/she may get infected but show no symptoms. This is because your vaccine-induced immune response is not able to stop every virus particle from replicating.

It is generally understood that a particular type of antibody known as a “neutralising antibody” is needed for sterilising immunity. These antibodies block virus entry into cells and prevent all replication. However, the infecting virus may have to be identical to the vaccine virus in order to induce the perfect antibody.

Interestingly, human immune responses to vaccines involve many different cells and components of the immune system. Even if the antibody response isn’t optimal, other aspects of immune memory can kick in when the virus invades. These, those who know better say, include cytotoxic T cells and non-neutralising antibodies. Viral replication will be slowed and consequently disease reduced.

Scientists say they know this from years of study on influenza vaccines. These vaccines typically induce protection from disease, but not necessarily protection from infection. This is largely due to the different strains of influenza that circulate—a situation that may also occur with SARS-CoV-2.

Perhaps, it is reassuring to note that flu vaccines, despite being unable to induce sterilising immunity, are still extremely valuable at controlling the virus.

In the absence of sterilising immunity, what effect might SARS-CoV-2 vaccines have on the spread of a virus through a population? If asymptomatic infections are possible after vaccination, there has been concern that SARS-CoV-2 will simply continue to infect as many people as before.

Is this possible?

Asymptomatically infected people typically produce virus at lower levels. Though there is not a perfect relationship, usually more virus equals more disease. Therefore, vaccinated people are less likely to transmit enough virus to cause severe disease.

This in turn means that the people getting infected in this situation are going to transmit less virus to the next susceptible person. This has been neatly shown experimentally using a vaccine targeting a different virus in chickens; when only part of a flock was vaccinated, unvaccinated birds still showed milder disease and produced less virus.

So, while sterilising immunity is often the ultimate goal of vaccine design, it is rarely achieved. Fortunately, this hasn’t stopped many different vaccines substantially reducing the number of cases of virus infections in the past.

Amazingly, by reducing disease levels in individuals, this also reduces virus spread through populations, and this will hopefully bring the current pandemic under control. Yet, for Nigeria, the Sonny Okosun question is still very germane: Which way to go

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