Infections and immunity

All throughout history, people have gone to extraordinary lengths to avoid infections.

In 1582, in Alghero, a town on the island of Sardinia, Italy, a plague outbreak killed more than half the population. If not for a quick-thinking doctor named Quinto Tiberio Angelerio, it could have been much worse.

Having worked in Sicily during a plague in 1575, Angelerio was familiar with signs of the disease and experienced in preventing its transmission. So, when three people died with plague-like symptoms, Angelerio asked the town leaders to isolate other patients. They called him alarmist, but the viceroy took it seriously.

The city was completely closed off, and guards patrolled the borders to ensure compliance.

It was reported that residents railed against the shutdown and threatened to lynch Angelerio. It was only after the plague had already spread throughout the city that the doctor was given the authority to institute further safety measures. He detailed his public health program in a 1588 pamphlet.

Some of his rules are medically dubious, to say the least, but his other instructions, detailed in a 2013 study published in Emerging Infectious Diseases, are surprisingly modern. “Meetings, dances, and entertainments are strictly forbidden,” he wrote, also encouraging citizens to disinfect anything that had been near an ill person. Everyone was confined to their houses, and anyone who needed to go shopping or any other necessary errand had to get permission from the “health guard”.

But permission was not enough. “People allowed to go out must bear with them a cane measuring 6-feet long” as “it is mandatory that people keep this distance from one another”. Maybe, like some modern-day physicians, he believed the air would not easily carry pathogens beyond that distance. In any case, the precaution seems prescient considering our current social distancing protocols.

While it is impossible to know how many lives Angelerio saved with his practices, or how many people actually ventured forth with 6-foot canes… the plague was gone from Alghero within about eight months. And during the 1650s, officials relied on Angelerio’s pamphlet to see them through another outbreak.

It is the immune system that helps to fight infections, defending the human body against invaders, such as viruses, bacteria, and foreign bodies.

Like many other parts of the body, our immune system shows signs of our ageing. Some of the immune cells lose their function.

Many infectious diseases are more severe in older adults than younger adults as a lifetime of exposure to diseases will increase the risk of future disease from new infections.

There is also immunosenescence, meaning they have a better immune memory for things they have been exposed to but are more limited when responding to new diseases.

As with other body parts, some people age better than others, either by looking after themselves or being lucky enough to have the right genetic make-up.

Effective or sterilising immunity?
There are two main types of immunity that you can achieve with vaccines. One is the so-called “effective immunity”, which can prevent a pathogen from causing serious disease, but cannot stop it from entering the body or making more copies of itself.

The other is “sterilising immunity”, which can avoid infections entirely and even prevent asymptomatic cases. Sterilising immunity is the aspiration of all vaccine research but, surprisingly, rarely achieved.

What type of immunity do the Covid-19 vaccines provide?
The truth is we do not know for sure, yet. Because they are too new, it cannot be guaranteed that the vacines might prevent the transmission of the virus, “however, it could significantly reduce illness”.

Does vaccination prevent infection and transmission?
As said above, we do not know whether the vaccines will prevent infection and protect against onward transmission. Although it is believed that immunity persists for several months, the full duration is not yet known. These are some of the important questions that are still being studied by scientists.

A crucial advantage of vaccines is that they provide the opportunity to generate immunity in large numbers of people, all at once. If few people are susceptible to a certain pathogen, there will not be much of it in circulation.

How effective is a single dose of a vaccine?
Is a person protected after the first shot of the Covid-19 vaccines? No!

What can you do after your first shot? Just pretend it did not happen!

There is only a one-dose shot vaccine. For the other vaccines, the second is essential for full protection. Preclinical trials have shown there was enough immunity after one shot.

People who are partly vaccinated should sit tight and not change their behavior until they have taken the two dosages.

How effective is a vaccine after the second dose?
It is after the second dose of an mRNA vaccine that protection against variants really kicks in as the second dose elicits a much more robust immune response.

Should a person have the second dose, even after having experienced side effects with the first dose, from arm soreness to fever and chills, lasting up to a day or two? YES!

The side effects are worth having to acquire that strong immune response that is going to effectively protect from the virus.

The vaccines give protection against the disease but not necessarily against carrying and transmitting the virus to the non-immunised, even without showing symptoms.

After the second dosage, the transmission potential is considered to be lower than for someone who has no immunity.

Hopeful results are that there are signs the RNA-messenger vaccines may block the virus transmission cycle between people, as well as reduce the viral load.

Is reinfection possible?
Scientists already know that the antibodies people develop after natural infections with Covid-19 do not always prevent from reinfection.

Most scientists are not expecting to eliminate the virus entirely. The actual goal is to reduce the transmission as much as possible. Once enough people have been vaccinated, it does not matter if they are still able to spread the virus. If only a few people are susceptible to a certain pathogen, there will not be much of it in circulation.

For those who are unable to be vaccinated, it may prove crucial that everyone else has immunity.

Another crucial advantage of vaccines is that they provide the opportunity to generate immunity in large numbers of people, all at once.

Getting the second dose is really important for lasting protection.

In the meantime, we must maintain public health measures that work: masking, physical distancing, handwashing, respiratory and cough hygiene, avoiding crowds, and ensuring good ventilation.

… which is more or less what Dr. Angelerio said in the 16th century!

People already had a pretty good idea that being infected was something to avoid at all costs – and this was centuries before we knew about microorganisms, antibodies or vaccination.

Best health wishes,
Dra. Maria Alice

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Dr Maria Alice is a consultant in General and Family Medicine. General Manager/Medical Director – Luzdoc International Medical Service. Medical Director – Grupo Hospital Particular do Algarve/ Hospital S. Gonçalo de Lagos